Earth

Common Misconceptions about Evolution

2010-09-01T05:38:00.001-07:00

Evolution can occur without morphological change; and morphological change can occur without evolution. Humans are larger now than in the recent past, a result of better diet and medicine. Phenotypic changes, like this, induced solely by changes in environment do not count as evolution because they are not heritable; in other words the change is not passed on to the organism's offspring. Phenotype is the morphological, physiological, biochemical, behavioral and other properties exhibited by a living organism. An organism's phenotype is determined by its genes and its environment. Most changes due to environment are fairly subtle, for example size differences. Large scale phenotypic changes are obviously due to genetic changes, and therefore are evolution.

Evolution is not progress. Populations simply adapt to their current surroundings. They do not necessarily become better in any absolute sense over time. A trait or strategy that is successful at one time may be unsuccessful at another. Paquin and Adams demonstrated this experimentally. They founded a yeast culture and maintained it for many generations. Occasionally, a mutation would arise that allowed its bearer to reproduce better than its contemporaries. These mutant strains would crowd out the formerly dominant strains. Samples of the most successful strains from the culture were taken at a variety of times. In later competition experiments, each strain would outcompete the immediately previously dominant type in a culture. However, some earlier isolates could outcompete strains that arose late in the experiment. Competitive ability of a strain was always better than its previous type, but competitiveness in a general sense was not increasing. Any organism's success depends on the behavior of its contemporaries. For most traits or behaviors there is likely no optimal design or strategy, only contingent ones. Evolution can be like a game of paper/scissors/rock.

Organisms are not passive targets of their environment. Each species modifies its own environment. At the least, organisms remove nutrients from and add waste to their surroundings. Often, waste products benefit other species. Animal dung is fertilizer for plants. Conversely, the oxygen we breathe is a waste product of plants. Species do not simply change to fit their environment; they modify their environment to suit them as well. Beavers build a dam to create a pond suitable to sustain them and raise young. Alternately, when the environment changes, species can migrate to suitable climes or seek out microenvironments to which they are adapted.

What is Evolution?

2010-09-01T05:34:00.000-07:00

Evolution is a change in the gene pool of a population over time. A gene is a hereditary unit that can be passed on unaltered for many generations. The gene pool is the set of all genes in a species or population.

The English moth, Biston betularia, is a frequently cited example of observed evolution. [evolution: a change in the gene pool] In this moth there are two color morphs, light and dark. H. B. D. Kettlewell found that dark moths constituted less than 2% of the population prior to 1848. The frequency of the dark morph increased in the years following. By 1898, the 95% of the moths in Manchester and other highly industrialized areas were of the dark type. Their frequency was less in rural areas. The moth population changed from mostly light colored moths to mostly dark colored moths. The moths' color was primarily determined by a single gene. [gene: a hereditary unit] So, the change in frequency of dark colored moths represented a change in the gene pool. [gene pool: the set all of genes in a population] This change was, by definition, evolution.

The increase in relative abundance of the dark type was due to natural selection. The late eighteen hundreds was the time of England's industrial revolution. Soot from factories darkened the birch trees the moths landed on. Against a sooty background, birds could see the lighter colored moths better and ate more of them. As a result, more dark moths survived until reproductive age and left offspring. The greater number of offspring left by dark moths is what caused their increase in frequency. This is an example of natural selection.

Populations evolve. [evolution: a change in the gene pool] In order to understand evolution, it is necessary to view populations as a collection of individuals, each harboring a different set of traits. A single organism is never typical of an entire population unless there is no variation within that population. Individual organisms do not evolve, they retain the same genes throughout their life. When a population is evolving, the ratio of different genetic types is changing -- each individual organism within a population does not change. For example, in the previous example, the frequency of black moths increased; the moths did not turn from light to gray to dark in concert. The process of evolution can be summarized in three sentences: Genes mutate. [gene: a hereditary unit] Individuals are selected. Populations evolve.

Evolution can be divided into microevolution and macroevolution. The kind of evolution documented above is microevolution. Larger changes, such as when a new species is formed, are called macroevolution. Some biologists feel the mechanisms of macroevolution are different from those of microevolutionary change. Others think the distinction between the two is arbitrary -- macroevolution is cumulative microevolution.

The word evolution has a variety of meanings. The fact that all organisms are linked via descent to a common ancestor is often called evolution. The theory of how the first living organisms appeared is often called evolution. This should be called abiogenesis. And frequently, people use the word evolution when they really mean natural selection -- one of the many mechanisms of evolution.

Accumulation of metals into the oceans

2010-09-01T05:27:00.000-07:00

In 1965, Chemical Oceanography published a list of some metals' "residency times" in the ocean. This calculation was performed by dividing the amount of various metals in the oceans by the rate at which rivers bring the metals into the oceans.

Several creationists have reproduced this table of numbers, claiming that these numbers gave "upper limits" for the age of the oceans (therefore the Earth) because the numbers represented the amount of time that it would take for the oceans to "fill up" to their present level of these various metals from zero.

First, let us examine the results of this "dating method." Most creationist works do not produce all of the numbers, only the ones whose values are "convenient." The following list is more complete:

Accumulation of meteoritic dust on the Moon

2010-09-01T05:25:00.000-07:00

The most common form of this young-Earth argument is based on a single measurement of the rate of meteoritic dust influx to the Earth gave a value in the millions of tons per year. While this is negligible compared to the processes of erosion on the Earth (about a shoebox-full of dust per acre per year), there are no such processes on the Moon. Young-Earthers claim that the Moon must receive a similar amount of dust (perhaps 25% as much per unit surface area due to its lesser gravity), and there should be a very large dust layer (about a hundred feet thick) if the Moon is several billion years old.

Decay of the Earth's magnetic field

2010-09-01T05:22:00.000-07:00

The young-Earth argument: the dipole component of the magnetic field has decreased slightly over the time that it has been measured. Assuming the generally accepted "dynamo theory" for the existence of the Earth's magnetic field is wrong, the mechanism might instead be an initially created field which has been losing strength ever since the creation event. An exponential fit (assuming a half-life of 1400 years on 130 years' worth of measurements) yields an impossibly high magnetic field even 8000 years ago, therefore the Earth must be young. The main proponent of this argument was Thomas Barnes.

There are several things wrong with this "dating" mechanism. It's hard to just list them all. The primary four are:

1.While there is no complete model to the geodynamo (certain key properties of the core are unknown), there are reasonable starts and there are no good reasons for rejecting such an entity out of hand. If it is possible for energy to be added to the field, then the extrapolation is useless.

2.There is overwhelming evidence that the magnetic field has reversed itself, rendering any unidirectional extrapolation on total energy useless. Even some young-Earthers admit to that these days -- e.g., Humphreys (1988).

3.Much of the energy in the field is almost certainly not even visible external to the core. This means that the extrapolation rests on the assumption that fluctuations in the observable portion of the field accurately represent fluctuations in its total energy.

4.Barnes' extrapolation completely ignores the nondipole component of the field. Even if we grant that it is permissible to ignore portions of the field that are internal to the core, Barnes' extrapolation also ignores portions of the field which are visible and instead rests on extrapolation of a theoretical entity.
That last part is more important than it may sound. The Earth's magnetic field is often split in two components when measured. The "dipole" component is the part which approximates a theoretically perfect field around a single magnet, and the "nondipole" components are the ("messy") remainder. A study in the 1960s showed that the decrease in the dipole component since the turn of the century had been nearly completely compensated by an increase in the strength of the nondipole components of the field. (In other words, the measurements show that the field has been diverging from the shape that would be expected of a theoretical ideal magnet, more than the amount of energy has actually been changing.) Barnes' extrapolation therefore does not really rest on the change in energy of the field.

How Old Is The Earth, And How Do We Know?

2010-09-01T05:18:00.000-07:00

he generally accepted age for the Earth and the rest of the solar system is about 4.55 billion years (plus or minus about 1%). This value is derived from several different lines of evidence.

Unfortunately, the age cannot be computed directly from material that is solely from the Earth. There is evidence that energy from the Earth's accumulation caused the surface to be molten. Further, the processes of erosion and crustal recycling have apparently destroyed all of the earliest surface.

The oldest rocks which have been found so far (on the Earth) date to about 3.8 to 3.9 billion years ago (by several radiometric dating methods). Some of these rocks are sedimentary, and include minerals which are themselves as old as 4.1 to 4.2 billion years. Rocks of this age are relatively rare, however rocks that are at least 3.5 billion years in age have been found on North America, Greenland, Australia, Africa, and Asia.

While these values do not compute an age for the Earth, they do establish a lower limit (the Earth must be at least as old as any formation on it). This lower limit is at least concordant with the independently derived figure of 4.55 billion years for the Earth's actual age.

The most direct means for calculating the Earth's age is a Pb/Pb isochron age, derived from samples of the Earth and meteorites. This involves measurement of three isotopes of lead (Pb-206, Pb-207, and either Pb-208 or Pb-204). A plot is constructed of Pb-206/Pb-204 versus Pb-207/Pb-204.

If the solar system formed from a common pool of matter, which was uniformly distributed in terms of Pb isotope ratios, then the initial plots for all objects from that pool of matter would fall on a single point.

Over time, the amounts of Pb-206 and Pb-207 will change in some samples, as these isotopes are decay end-products of uranium decay (U-238 decays to Pb-206, and U-235 decays to Pb-207). This causes the data points to separate from each other. The higher the uranium-to-lead ratio of a rock, the more the Pb-206/Pb-204 and Pb-207/Pb-204 values will change with time.

Earth's electromagnetic field

2010-08-27T01:46:00.001-07:00

An electromagnet is a magnet that is created by a current that flows around a soft-iron core.[18] Earth has a soft iron core surrounded by semi-liquid materials from the mantle that move in continuous currents around the core;[19] therefore, the earth is an electromagnet. This is referred to as the dynamo theory of Earth's magnetism.[20][21] The fact that Earth is an electromagnet helps it maintain an atmosphere suitable for life.

Earth's interior

2010-08-27T01:41:00.000-07:00

Plate tectonics, mountain ranges, volcanoes, and earthquakes are geological phenomena that can be explained in terms of energy transformations in the Earth's crust.[9]

Beneath the Earth's crust lies the mantle which is heated by the radioactive decay of heavy elements. The mantle is not quite solid and consists of magma which is in a state of semi-perpetual convection. This convection process causes the lithospheric plates to move, albeit slowly. The resulting process is known as plate tectonics.[10][11][12][13]

Plate tectonics might be thought of as the process by which the earth is resurfaced. Through a process called spreading ridges (or seafloor spreading), new earth crust is created by the flow of magma from underneath the lithosphere to the surface, through fissures, where it cools and solidifies. Through a process called subduction, crust is pushed underground—beneath the rest of the lithosphere—where it comes into contact with magma and melts—rejoining the mantle from which it originally came.[11][13][14]

Areas of the crust where new crust is created are called divergent boundaries, and areas of the crust where it is brought back into the earth are called convergent boundaries.[15][16] Earthquakes result from the movement of the lithospheric plates, and they often occur near covergent boundaries where parts of the crust are forced into the earth as part of subduction.[17]

Volcanoes result primarily from the melting of subducted crust material. Crust material that is forced into the Asthenosphere melts, and some portion of the melted material becomes light enough to rise to the surface—giving birth to volcanoes.

Earth science

2010-08-27T01:38:00.000-07:00

Earth science (also known as geoscience, the geosciences or the Earth sciences), is an all-embracing term for the sciences related to the planet Earth.[1] It is arguably a special case in planetary science, the Earth being the only known life-bearing planet. There are both reductionist and holistic approaches to Earth sciences. The formal discipline of Earth sciences may include the study of the atmosphere, oceans and biosphere, as well as the solid earth. Typically Earth scientists will use tools from physics, chemistry, biology, chronology and mathematics to build a quantitative understanding of how the Earth system works, and how it evolved to its current state.

Physics

2010-08-27T01:29:00.000-07:00

Physics embodies the study of the fundamental constituents of the universe, the forces and interactions they exert on one another, and the results produced by these interactions. In general, physics is regarded as the fundamental science, because all other natural sciences use and obey the principles and laws set down by the field. Physics relies heavily on mathematics as the logical framework for formulation and quantification of principles.

The study of the principles of the universe has a long history and largely derives from direct observation and experimentation. The formulation of theories about the governing laws of the universe has been central to the study of physics from very early on, with philosophy gradually yielding to systematic, quantitative experimental testing and observation as the source of verification.

Key historical developments in physics include Isaac Newton's theory of universal gravitation and classical mechanics, an understanding of electricity and its relation to magnetism, Einstein's theories of special and general relativity, the development of thermodynamics, and the quantum mechanical model of atomic and subatomic physics.

The field of physics is extremely broad, and can include such diverse studies as quantum mechanics and theoretical physics, applied physics and optics. Modern physics is becoming increasingly specialized, where researchers tend to focus on a particular area rather than being "universalists" like Albert Einstein and Lev Landau, who worked in multiple areas.

Earth science

2010-08-27T01:26:00.001-07:00

Earth science (also known as geoscience, the geosciences or the Earth Sciences), is an all-embracing term for the sciences related to the planet Earth, including geology, geophysics, hydrology, meteorology, physical geography, oceanography, and soil science.

Although mining and precious stones have been human interests throughout the history of civilization, the development of the related sciences of economic geology and mineralogy did not occur until the 18th century. The study of the earth, particularly palaeontology, blossomed in the 19th century. The growth of other disciplines, such as geophysics, in the 20th century led to the development of the theory of plate tectonics in the 1960s, which has had a similar effect on the Earth sciences as the theory of evolution had on biology. Earth sciences today are closely linked to climate research and the petroleum and mineral exploration industries

Chemistry

2010-08-27T01:24:00.000-07:00

Constituting the scientific study of matter at the atomic and molecular scale, chemistry deals primarily with collections of atoms, such as gases, molecules, crystals, and metals. The composition, statistical properties, transformations and reactions of these materials are studied. Chemistry also involves understanding the properties and interactions of individual atoms for use in larger-scale applications.

Most chemical processes can be studied directly in a laboratory, using a series of (often well-tested) techniques for manipulating materials, as well as an understanding of the underlying processes. Chemistry is often called "the central science" because of its role in connecting the other natural sciences.

Early experiments in chemistry had their roots in the system of Alchemy, a set of beliefs combining mysticism with physical experiments. The science of chemistry began to develop with the work of Robert Boyle, the discoverer of gas, and Antoine Lavoisier, who developed the theory of the Conservation of mass.

The discovery of the chemical elements and the concept of Atomic Theory began to systematize this science, and researchers developed a fundamental understanding of states of matter, ions, chemical bonds and chemical reactions. The success of this science led to a complementary chemical industry that now plays a significant role in the world economy.

Biology

2010-08-27T01:23:00.001-07:00

This field encompasses a set of disciplines that examines phenomena related to living organisms. The scale of study can range from sub-component biophysics up to complex ecologies. Biology is concerned with the characteristics, classification and behaviors of organisms, as well as how species were formed and their interactions with each other and the environment.

The biological fields of botany, zoology, and medicine date back to early periods of civilization, while microbiology was introduced in the 17th century with the invention of the microscope. However, it was not until the 19th century that biology became a unified science. Once scientists discovered commonalities between all living things, it was decided they were best studied as a whole.

Some key developments in biology were the discovery of genetics; Darwin's theory of evolution through natural selection; the germ theory of disease and the application of the techniques of chemistry and physics at the level of the cell or organic molecule.

Modern biology is divided into subdisciplines by the type of organism and by the scale being studied. Molecular biology is the study of the fundamental chemistry of life, while cellular biology is the examination of the cell; the basic building block of all life. At a higher level, physiology looks at the internal structure of organism, while ecology looks at how various organisms interrelate.

Astronomy

2010-08-27T01:22:00.001-07:00

This discipline is the science of celestial objects and phenomena that originate outside the Earth's atmosphere. It is concerned with the evolution, physics, chemistry, meteorology, and motion of celestial objects, as well as the formation and development of the universe.

Astronomy includes the examination, study and modeling of stars, planets, comets, galaxies and the cosmos. Most of the information used by astronomers is gathered by remote observation, although some laboratory reproduction of celestial phenomenon has been performed (such as the molecular chemistry of the interstellar medium).

While the origins of the study of celestial features and phenomenon can be traced back to antiquity, the scientific methodology of this field began to develop in the middle of the 17th century. A key factor was Galileo's introduction of the telescope to examine the night sky in more detail.

The mathematical treatment of astronomy began with Newton's development of celestial mechanics and the laws of gravitation, although it was triggered by earlier work of astronomers such as Kepler. By the 19th century, astronomy had developed into a formal science, with the introduction of instruments such as the spectroscope and photography, along with much-improved telescopes and the creation of professional observatories

History

2010-08-27T01:21:00.000-07:00

In ancient and medieval times, the objective study of nature was known as natural philosophy. In late medieval and early modern times, a philosophical interpretation of nature was gradually replaced by a scientific approach using inductive methodology. The works of Ibn al-Haytham and Sir Francis Bacon popularized this approach, thereby helping to forge the scientific revolution.

By the 19th century, the study of science had come into the purview of professionals and institutions. In so doing, it gradually acquired the more modern name of natural science. The term scientist was coined by William Whewell in an 1834 review of Mary Somerville's On the Connexion of the Sciences. But the word did not enter general use until nearly the end of the same century.

According to a famous 1923 textbook Thermodynamics — and the Free Energy of Chemical Substances by the American chemist Gilbert N. Lewis and the American physical chemist Merle Randall, the natural sciences contain three great branches:

Aside from the logical and mathematical sciences, there are three great branches of natural science which stand apart by reason of the variety of far reaching deductions drawn from a small number of primary postulates — they are mechanics, electrodynamics, and thermodynamics

Overview

2010-08-27T01:20:00.001-07:00

Natural sciences form the basis for applied sciences. Together, the natural and applied sciences are distinguished from the social sciences on the one hand, and the humanities on the other. Though mathematics, statistics, and computer science are not considered natural sciences (mathematics traditionally considered among the liberal arts and statistics among the humanities, for instance), they provide many tools and frameworks used within the natural sciences.

Alongside this traditional usage, the phrase natural sciences is also sometimes used more narrowly to refer to natural history. In this sense "natural sciences" may refer to the biology and perhaps also the earth sciences, as distinguished from the physical sciences, including astronomy, physics, and chemistry.

Within the natural sciences, the term hard science is sometimes used to describe those subfields which some people view as relying on experimental, quantifiable data or the scientific method and focus on accuracy and objectivity. These usually include physics, chemistry and biology. By contrast, soft science is often used to describe the scientific fields that are more reliant on qualitative research, including the social sciences.

Natural science

2010-08-27T01:18:00.000-07:00

In science, the term natural science refers to a naturalistic approach to the study of the universe, which is understood as obeying rules or laws of natural origin.

The term natural science is also used to distinguish those fields that use the scientific method to study nature from the social sciences, which use the scientific method to study human behavior and society; from the formal sciences, such as mathematics and logic, which use a different (a priori) methodology; from the Sacred Sciences and from the humanities.

Natural resources and land use

2010-06-23T01:54:00.000-07:00

The Earth provides resources that are exploitable by humans for useful purposes. Some of these are non-renewable resources, such as mineral fuels, that are difficult to replenish on a short time scale.

Large deposits of fossil fuels are obtained from the Earth's crust, consisting of coal, petroleum, natural gas and methane clathrate. These deposits are used by humans both for energy production and as feedstock for chemical production. Mineral ore bodies have also been formed in Earth's crust through a process of Ore genesis, resulting from actions of erosion and plate tectonics.[145] These bodies form concentrated sources for many metals and other useful elements.

The Earth's biosphere produces many useful biological products for humans, including (but far from limited to) food, wood, pharmaceuticals, oxygen, and the recycling of many organic wastes. The land-based ecosystem depends upon topsoil and fresh water, and the oceanic ecosystem depends upon dissolved nutrients washed down from the land.[146] Humans also live on the land by using building materials to construct shelters. In 1993, human use of land is approximately:

Land use Percentage
Arable land 13.13%[10]
Permanent crops 4.71%[10]
Permanent pastures 26%
Forests and woodland 32%
Urban areas 1.5%
Other 30%

The estimated amount of irrigated land in 1993 was 2,481,250km

Weather and climate

2010-06-23T01:53:00.000-07:00

The Earth's atmosphere has no definite boundary, slowly becoming thinner and fading into outer space. Three-quarters of the atmosphere's mass is contained within the first 11 km of the planet's surface. This lowest layer is called the troposphere. Energy from the Sun heats this layer, and the surface below, causing expansion of the air. This lower density air then rises, and is replaced by cooler, higher density air. The result is atmospheric circulation that drives the weather and climate through redistribution of heat energy.[106]

The primary atmospheric circulation bands consist of the trade winds in the equatorial region below 30° latitude and the westerlies in the mid-latitudes between 30° and 60°.[107] Ocean currents are also important factors in determining climate, particularly the thermohaline circulation that distributes heat energy from the equatorial oceans to the polar regions.[108]

Source regions of global air massesWater vapor generated through surface evaporation is transported by circulatory patterns in the atmosphere. When atmospheric conditions permit an uplift of warm, humid air, this water condenses and settles to the surface as precipitation.[106] Most of the water is then transported to lower elevations by river systems and usually returned to the oceans or deposited into lakes. This water cycle is a vital mechanism for supporting life on land, and is a primary factor in the erosion of surface features over geological periods. Precipitation patterns vary widely, ranging from several meters of water per year to less than a millimeter. Atmospheric circulation, topological features and temperature differences determine the average precipitation that falls in each region.[109]

The Earth can be sub-divided into specific latitudinal belts of approximately homogeneous climate. Ranging from the equator to the polar regions, these are the tropical (or equatorial), subtropical, temperate and polar climates.[110] Climate can also be classified based on the temperature and precipitation, with the climate regions characterized by fairly uniform air masses. The commonly used Köppen climate classification system (as modified by Wladimir Köppen's student Rudolph Geiger) has five broad groups (humid tropics, arid, humid middle latitudes, continental and cold polar), which are further divided into more specific subtypes.

Atmosphere

2010-06-23T01:52:00.000-07:00

The atmospheric pressure on the surface of the Earth averages 101.325 kPa, with a scale height of about 8.5 km.[3] It is 78% nitrogen and 21% oxygen, with trace amounts of water vapor, carbon dioxide and other gaseous molecules. The height of the troposphere varies with latitude, ranging between 8 km at the poles to 17 km at the equator, with some variation resulting from weather and seasonal factors.[104]

Earth's biosphere has significantly altered its atmosphere. Oxygenic photosynthesis evolved 2.7 billion years ago, forming the primarily nitrogen-oxygen atmosphere of today. This change enabled the proliferation of aerobic organisms as well as the formation of the ozone layer which blocks ultraviolet solar radiation, permitting life on land. Other atmospheric functions important to life on Earth include transporting water vapor, providing useful gases, causing small meteors to burn up before they strike the surface, and moderating temperature.[105] This last phenomenon is known as the greenhouse effect: trace molecules within the atmosphere serve to capture thermal energy emitted from the ground, thereby raising the average temperature. Carbon dioxide, water vapor, methane and ozone are the primary greenhouse gases in the Earth's atmosphere. Without this heat-retention effect, the average surface temperature would be −18 °C and life would likely not exist.

Shape

2010-06-23T01:51:00.000-07:00

The shape of the Earth is very close to that of an oblate spheroid, a sphere flattened along the axis from pole to pole such that there is a bulge around the equator.[59] This bulge results from the rotation of the Earth, and causes the diameter at the equator to be 43 km larger than the pole to pole diameter.[60] The average diameter of the reference spheroid is about 12,742 km, which is approximately 40,000 km/π, as the meter was originally defined as 1/10,000,000 of the distance from the equator to the North Pole through Paris, France.[61]

Local topography deviates from this idealized spheroid, though on a global scale, these deviations are very small: Earth has a tolerance of about one part in about 584, or 0.17%, from the reference spheroid, which is less than the 0.22% tolerance allowed in billiard balls.[62] The largest local deviations in the rocky surface of the Earth are Mount Everest (8848 m above local sea level) and the Mariana Trench (10,911 m below local sea level). Because of the equatorial bulge, the surface locations farthest from the center of the Earth are the summits of Mount Chimborazo in Ecuador and Huascarán in Peru.

Composition and structure

2010-06-23T01:50:00.000-07:00

Earth is a terrestrial planet, meaning that it is a rocky body, rather than a gas giant like Jupiter. It is the largest of the four solar terrestrial planets in size and mass. Of these four planets, Earth also has the highest density, the highest surface gravity, the strongest magnetic field, and fastest rotation.[57] It also is the only terrestrial planet with active plate tectonics.

Future

2010-06-23T01:48:00.000-07:00

The future of the planet is closely tied to that of the Sun. As a result of the steady accumulation of helium at the Sun's core, the star's total luminosity will slowly increase. The luminosity of the Sun will grow by 10% over the next 1.1 Gyr (1.1 billion years) and by 40% over the next 3.5 Gyr.[49] Climate models indicate that the rise in radiation reaching the Earth is likely to have dire consequences, including the loss of the planet's oceans.[50]

The Earth's increasing surface temperature will accelerate the inorganic CO2 cycle, reducing its concentration to levels lethally low for plants (10 ppm for C4 photosynthesis) in approximately 500 million[19] to 900 million years. The lack of vegetation will result in the loss of oxygen in the atmosphere, so animal life will become extinct within several million more years.[51] After another billion years all surface water will have disappeared[21] and the mean global temperature will reach 70 °C[51](158 °F). The Earth is expected to be effectively habitable for about another 500 million years from that point,[19] although this may be extended up to 2.3 billion years if the nitrogen is removed from the atmosphere.[52] Even if the Sun were eternal and stable, the continued internal cooling of the Earth would result in a loss of much of its CO2 due to reduced volcanism,[53] and 35% of the water in the oceans would descend to the mantle due to reduced steam venting from mid-ocean ridges.[54]

The Sun, as part of its evolution, will become a red giant in about 5 Gyr. Models predict that the Sun will expand out to about 250 times its present radius, roughly 1 AU (150,000,000 km).[49][55] Earth's fate is less clear. As a red giant, the Sun will lose roughly 30% of its mass, so, without tidal effects, the Earth will move to an orbit 1.7 AU (250,000,000 km) from the Sun when the star reaches it maximum radius. The planet was therefore initially expected to escape envelopment by the expanded Sun's sparse outer atmosphere, though most, if not all, remaining life would have been destroyed by the Sun's increased luminosity (peaking at about 5000 times its present level).[49] However, a more recent simulation indicates that Earth's orbit will decay due to tidal effects and drag, causing it to enter the red giant Sun's atmosphere and be vaporized.[55]

Possible alternatives to this fate include the purposeful displacement of an asteroid from the Kuiper belt, which would repeatedly fly close enough to Earth as to enlarge its orbit, thereby preventing the overheating of its surface. The lifespan of the biosphere could thereby be extended by 5 billion years.

21st Century

2010-06-23T01:47:00.000-07:00

With the discovery during the latter half of the 20th century of more objects within the Solar System and large objects around other stars, disputes arose over what should constitute a planet. There was particular disagreement over whether an object should be considered a planet if it was part of a distinct population such as a belt, or if it was large enough to generate energy by the thermonuclear fusion of deuterium.

A growing number of astronomers argued for Pluto to be declassified as a planet, since many similar objects approaching its size had been found in the same region of the Solar System (the Kuiper belt) during the 1990s and early 2000s. Pluto was found to be just one small body in a population of thousands.

Some of them including Quaoar, Sedna, and Eris were heralded in the popular press as the tenth planet, failing however to receive widespread scientific recognition. The announcement of Eris in 2005, an object 27 percent more massive than Pluto, created the necessity and public desire for an official definition of a planet.

Acknowledging the problem, the IAU set about creating the definition of planet, and produced one in August 2006. The number of planets dropped to the eight significantly larger bodies that had cleared their orbit (Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, and Neptune), and a new class of dwarf planets was created, initially containing three objects (Ceres, Pluto and Eris).

20th Century

2010-06-23T01:46:00.000-07:00

However, in the 20th century, Pluto was discovered. After initial observations led to the belief it was larger than Earth,[30] the object was immediately accepted as the ninth planet. Further monitoring found the body was actually much smaller: in 1936, Raymond Lyttleton suggested that Pluto may be an escaped satellite of Neptune,[31] and Fred Whipple suggested in 1964 that Pluto may be a comet.[32] However, as it was still larger than all known asteroids and seemingly did not exist within a larger population,[33] it kept its status until 2006.

Planets from 1930 to 2006 Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune Pluto

In 1992, astronomers Aleksander Wolszczan and Dale Frail announced the discovery of planets around a pulsar, PSR B1257+12.[34] This discovery is generally considered to be the first definitive detection of a planetary system around another star. Then, on October 6, 1995, Michel Mayor and Didier Queloz of the University of Geneva announced the first definitive detection of an exoplanet orbiting an ordinary main-sequence star (51 Pegasi).[35]

The discovery of extrasolar planets led to another ambiguity in defining a planet; the point at which a planet becomes a star. Many known extrasolar planets are many times the mass of Jupiter, approaching that of stellar objects known as "brown dwarfs".[36] Brown dwarfs are generally considered stars due to their ability to fuse deuterium, a heavier isotope of hydrogen. While stars more massive than 75 times that of Jupiter fuse hydrogen, stars of only 13 Jupiter masses can fuse deuterium. However, deuterium is quite rare, and most brown dwarfs would have ceased fusing deuterium long before their discovery, making them effectively indistinguishable from supermassive planets.[37]

19th Century

2010-06-23T01:44:00.000-07:00

In the 19th century astronomers began to realize that recently discovered bodies that had been classified as planets for almost half a century (such as Ceres, Pallas, and Vesta) were very different from the traditional ones. These bodies shared the same region of space between Mars and Jupiter (the Asteroid belt), and had a much smaller mass; as a result they were reclassified as "asteroids." In the absence of any formal definition, a "planet" came to be understood as any "large" body that orbited the Sun. Since there was a dramatic size gap between the asteroids and the planets, and the spate of new discoveries seemed to have ended after the discovery of Neptune in 1846, there was no apparent need to have a formal definitio

Earth History

2010-06-19T21:58:00.000-07:00

Investigate sedimentary rocks and fossils from the Grand Canyon and consider the processes that shape the land to discover clues that reveal Earth's history.

Our close proximity prevents us from seeing Earth in its entirety

2010-06-16T19:51:00.000-07:00

To completely view our own planet, we must leave its surface and journey into space. From the vantage point of space we are able to observe our planet globally, as we do other planets, using similar sensitive instruments to understand the delicate balance among its oceans, air, land, and life. Viewing Earth from the unique perspective of space provides the opportunity to see Earth as a whole. Scientists around the world have discovered many things about our planet by working together and sharing their findings.

Earth has a magnetic field

2010-06-16T19:50:00.000-07:00

Our planet's rapid spin and molten nickel-iron core give rise to a magnetic field, which the solar wind distorts into a teardrop shape. The magnetic field does not fade off into space, but has definite boundaries. Just like the field around a magnet, ours is also polarized. When charged particles from the solar wind become trapped in Earth's magnetic field, they collide with air molecules above our planet's magnetic poles. These air molecules then begin to glow and are known as the aurorae, or the Northern and Southern Lights.

Earth has one natural satellite

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Earth's Moon (called Luna) orbits at a distance of 384,000km, with a radius of 1738KM and a mass of 7.32e22kg. However, there are thousands of small artificial satellites which have been placed in orbit around the Earth. Also, asteroids 3753 Cruithne and 2002 AA29 have complicated orbital relationships with the Earth; they're not really moons, the term "companion" is being used.
Because of its size and rocky composition, the moon has also been called a terrestrial planet along with Mercury, Venus, Earth, and Mars. It has no atmosphere, but there is water ice in some deep craters. The moon is the only extra-planetary body that a human has visited.

Earth has an atmosphere that sustains life

2010-06-16T19:47:00.001-07:00

Earth's atmosphere is 77% nitrogen, 21% oxygen, with traces of argon, carbon dioxide and water. This atmosphere affects Earth's long-term climate and short-term local weather; shields us from nearly all harmful radiation coming from the Sun; and protects us from meteors as well - most of which burn up before they can strike the surface.

Earth has four distinct seasons

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This is a result of a result of Earth's axis of rotation being tilted more than 23 degrees. Seasons changes as the tilt of Earth's axis changes during it's revolution around the Sun.

Early philosophy had the Earth as the center of the universe

2010-06-16T19:44:00.001-07:00

Although Aristarchus of Samos, in the 3rd Century B.C., figured out how to measure the distances to and sizes of the Sun and the Moon, and concluded that the Earth orbited the Sun, this view didn't attract followers until Nicolaus Copernicus, a Polish astronomer, published "On the Revolutions of the Celestial Spheres" in 1543.

Earth is mostly covered in water

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While the word earth is often used synonymously with dirt, seventy-one percent of the its surface is covered with water. It is the only planet where it exists in its liquid form on the surface. This is probably part of the reason that the Earth is the only planet known to contain life.

Earth is the only planet known to harbor life

2010-06-16T19:41:00.000-07:00

All of the things we need to survive are provided under a thin layer of atmosphere that separates us from the uninhabitable void of space. Earth is made up of complex, interactive systems that are often unpredictable. Air, water, land, and life - including humans - combine forces to create a constantly changing world that we are striving to understand.

Earth is the fifth largest planet

2010-06-16T19:40:00.001-07:00

The diameter of the earth at the equator is about 7926 miles, but that's not the whole story. Because the earth is not a perfect sphere but is slightly flattened at the poles, the diameter of the earth measured around the North Pole and the South Pole is about 7899 miles.

Earth is the third planet from the Sun

2010-06-16T19:37:00.000-07:00

The Earth's average distance from the Sun is 149,597,890 km (92,955,820 miles) or one astronomical unit (AU). Located between Venus and Mars, some people have called it the "third rock from the sun."
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The Environment and World History

2010-06-16T03:39:00.000-07:00

Since around 1500 C.E., humans have shaped the global environment in ways that were previously unimaginable. Bringing together leading environmental historians and world historians, this book offers an overview of global environmental history throughout this remarkable 500-year period. In eleven essays, the contributors examine the connections between environmental change and other major topics of early modern and modern world history: population growth, commercialization, imperialism, industrialization, the fossil fuel revolution, and more. Rather than attributing environmental change largely to European science, technology, and capitalism, the essays illuminate a series of culturally distinctive, yet often parallel developments arising in many parts of the world, leading to intensified exploitation of land and water. The wide range of regional studies—including some in Russia, China, the Middle East, India, Southeast Asia, Latin America, Southern Africa, and Western Europe—together with the book's broader thematic essays makes The Environment and World History ideal for courses that seek to incorporate the environment and environmental change more fully into a truly integrative understanding of world history.

Food and the future

2010-06-16T03:38:00.000-07:00

From BSE to GM, food is news. This focus brings together what seems to be a disparate selection of material recently published in Nature, illustrating, as well as anything can, how issues relating to food touch every sphere of human life.

Sustainable development

2010-06-16T03:37:00.002-07:00

Reporting from the Johannesburg summit in 2002, Nature presents news, features and research on sustainable development

Climate and water

2010-06-16T03:37:00.001-07:00

A specially commissioned Insight on Climate and Water, together with a selection of recent articles handpicked from the pages of Nature, illuminating the connections between climate and water in ice, oceans and atmosphere.

Global water crisis

2010-06-16T03:36:00.002-07:00

More then one billion people in the world lack access to clean water, and things are getting worse. Read Nature's analysis of the global water crisis with a collection of news, features and interactive graphics.

GM crops: Time to choose

2010-06-16T03:36:00.001-07:00

Today, just four countries account for 99% of the world's commercially grown transgenic crops. Others have been stalling over whether to embrace transgenic agriculture, but won't be able to put off the decision much longer. Here, Nature examines the state of play with special features and interactive graphics.

Fossil fuels

2010-06-16T03:35:00.002-07:00

The exploitation of fossil fuels to satisfy the majority of our energy needs drives continued and often heated public debate. Nature presents a focus on some of the many issues surrounding hydrocarbon fuel usage, from the economic, social and environmental impact to future energy resources.

Organic farming

2010-06-16T03:35:00.001-07:00

Is organic the future of farming? In its pure form, maybe not. But elements of the organic philosophy are starting to be deployed in mainstream agriculture. Here, Nature analyses this trend, assesses the extent of organic farming, and frames the questions on which its wider adoption will depend.

Ice Cores

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Ice cores give a glimpse of the dramatic variations in climate that accompanied past ice ages. Even better, these frozen climate records can reveal much about the levels of atmospheric greenhouse gases while temperatures changed. Here Nature brings together groundbreaking new sets of results from both polar regions together with previous classic papers and other ice-core related articles.

Energy for a cool planet

2010-06-16T03:32:00.000-07:00

The most pressing technological problem facing the world is uncoupling the provision of energy from the production of carbon dioxide. Developed countries no longer need to increase their energy use in order to increase the size of their economies, but developing countries do. And yet to add more carbon dioxide to the Earth's atmosphere is to increase inexorably the chances of climatic chaos.

Earth and environment archive

2010-06-16T03:28:00.000-07:00

EPICA Dome C: Greenhouse gases over eight glacial cycles
Ice cores are invaluable archives of past environmental conditions on Earth. In 1996, the European Project for Ice Coring in Antarctica (EPICA) set out to provide the longest ice-core climate record yet, by drilling a core from 3,270 m thick ice at a site known as Dome C in East Antarctica. The team's findings to date, including a complete Antarctic climate record over the past 800,000 years and atmospheric methane and carbon dioxide records from 650,000 years ago to the present, have significantly advanced our understanding of the Earth's climate over the past eight glacial cycles. Here Nature presents the latest results, the complete records of atmospheric methane and carbon dioxide over the past 800,000 years, along with some of the previous Dome C ice-core papers and a collection of related articles.

What is Earth made of?

2010-06-14T23:03:00.000-07:00

The Earth is made out of many things. Deep inside Earth, near its center, lies Earth's core which is mostly made up of nickel and iron. Above the core is Earth's mantle, which is made up of rock containing silicon, iron, magnesium, aluminum, oxygen and other minerals. The rocky surface layer of Earth, called the crust, is made up of mostly oxygen, silicon, aluminum, iron, calcium, sodium, potassium and magnesium. Earth's surface is mainly covered with liquid water and its atmosphere is is mainly nitrogen and oxygen, with smaller amounts of carbon dioxide, water vapor and other gases.

Earth first anamils

2010-06-14T22:48:00.000-07:00

A new study mapping the evolutionary history of animals indicates that Earth's first animal -- a mysterious creature whose characteristics can only be inferred from fossils and studies of living animals--was probably significantly more complex than previously believed.
Using new high-powered technologies for analyzing massive volumes of genetic data, the study defined the earliest splits at the base of the animal tree of life. The tree of life is a hierarchical representation of the evolutionary relationships between species that was introduced by Charles Darwin.
The study is published in the April 10, 2008 issue of Nature.

The Mesozoic Era

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Following the Permian extinction, the fossil record shows that reptiles became the dominant animals on land. The most spectacular of these reptiles were the dinosaurs. The Mesozoic is often called the Age of the Dinosaurs, but mammals and birds also appear in the fossil record in rocks from 200 million to 140 million years old.
Fossil plants of the Mesozoic Era represent two main groups, gymnosperms and angiosperms. Gymnosperms have naked seeds, and most are cone-bearing. They include conifers, ginkgoes, and cycads. These gymnosperms evolved in the later part of the Paleozoic Era and were dominant into the early Cretaceous Period. Angiosperms have covered seeds and are flowering plants. They became the dominant plant group during the Cretaceous Period and continue to be so today.
The dinosaurs died out in another great extinction about 65 million years ago. Most scientists believe that the extinction was caused by the impact of a small asteroid with Earth. The impact would have thrown so much dust into the atmosphere that the surface would have been dark and cold for months, killing off plants and the animals that fed on them. Many scientists believe a large, buried crater in the Yucatan region of Mexico, called Chicxulub (CHEEK shoo loob), is the place the asteroid struck. Debris from the collision has been found all over the world, and deposits created by large sea waves caused by the impact have been found in several places around the Gulf of Mexico.

Life on Earth

2010-06-14T22:46:00.001-07:00

Many rocks contain fossils that reveal the history of life on Earth. A fossil may be an animal's body, a tooth, or a piece of bone. It may simply be an impression of a plant or an animal made in a rock when the rock was soft sediment. Fossils help scientists learn which kinds of plants and animals lived at different times in Earth's history. Scientists who study prehistoric life are called paleontologists.
Many scientists believe that life appeared on Earth almost as soon as conditions allowed. There is evidence for chemicals created by living things in rocks from the Archean age, 3.8 billion years old. Fossil remains of microscopic living things about 3.5 billion years old have also been found at sites in Australia and Canada.
For most of Earth's history, life consisted mainly of microscopic, single-celled creatures. The earliest fossils of larger creatures with many cells are found in Precambrian rocks that are about 600 million years old. Many of these creatures differed from any living things today.

History of Earth

2010-06-14T22:44:00.000-07:00

The history of Earth is recorded in the rocks of Earth's crust. Rocks have been forming, wearing away, and re-forming ever since Earth took shape. The products of weathering and erosion are called sediment. Sediment accumulates in layers known as strata. Strata contain clues that tell geologists about Earth's past. These clues include the composition of the sediment, the way the strata are deposited, and the kinds of fossils that may occur in the rock.
Space exploration has expanded our understanding of Earth's origin. The Hubble Space Telescope has observed what appear to be stars in the process of forming planets. Since the mid-1990's, scientists have found other stars that have planets surrounding them. These discoveries have helped scientists develop theories about the formation of Earth.

Earth's rocks

2010-06-14T22:42:00.000-07:00

The solid part of Earth consists of rocks, which are sometimes made up of a single mineral, but more often consist of mixtures of minerals. Geologists classify rocks according to their origin. Igneous rocks form when molten rock cools and solidifies. Sedimentary rocks form when grains of rock or dissolved chemicals are deposited in layers by wind, water, or glaciers. Over time, the layers harden into solid rock. Metamorphic rocks develop deep in Earth's crust when heat or pressure transform other types of rock.
Igneous rocks form from molten material called magma. Most of Earth's interior is solid, not molten, but it is extremely hot. At the base of Earth's crust, the temperature is about 1800 degrees F (1000 degrees C). In some portions of the crust, conditions are right for rocks to melt. Rocks can melt more easily near the crust if they contain water, which lowers their melting point.
Where conditions are right, small pockets of magma form beneath and within the crust. Some of this magma reaches the surface, where it erupts from volcanoes as lava. Igneous rocks formed this way are called volcanic or extrusive. Vast quantities of magma, however, never reach the surface. They cool slowly within the crust and may only be exposed long afterward by erosion. Such igneous rocks are called plutonic or intrusive. Plutonic rocks cool slowly. During this slow cooling, their minerals form large crystals. Plutonic rocks tend to be much coarser than volcanic rocks.
Igneous rocks that are rich in silica tend to be poor in iron and magnesium, and the opposite is also true. Volcanic rocks that are iron-rich and silica-poor are basalt. Plutonic rocks of the same makeup are called gabbro. Silica-rich volcanic rocks are called rhyolite (RY uh lyt), and plutonic rocks of the same composition are granite. Granite lies under most of the continents, while basalt lies under most of the ocean floors.

The atmosphere

2010-06-14T22:40:00.001-07:00

Air surrounds Earth and becomes progressively thinner farther from the surface. Most people find it difficult to breathe more than 2 miles (3 kilometers) above sea level. About 100 miles (160 kilometers) above the surface, the air is so thin that satellites can travel without much resistance. Detectable traces of atmosphere, however, can be found as high as 370 miles (600 kilometers) above Earth's surface. The atmosphere has no definite outer edge but fades gradually into space.
Nitrogen makes up 78 percent of the atmosphere, while oxygen makes up 21 percent. The remaining 1 percent consists of argon and small amounts of other gases. The atmosphere also contains water vapor, carbon dioxide, water droplets, dust particles, and small amounts of many other chemicals released by volcanoes, fires, living things, and human activities.
The lowest layer of the atmosphere is called the troposphere. This layer is in constant motion. The sun heats Earth's surface and the air above it, causing warm air to rise. As the warm air rises, air pressure decreases and the air expands and cools. The cool air is denser than the surrounding air, so it sinks and the cycle starts again. This constant cycle of the air causes the weather.
High above the troposphere, about 30 miles (48 kilometers) above Earth's surface, is a layer of still air called the stratosphere. The stratosphere contains a layer where ultraviolet light from the sun strikes oxygen molecules to create a gas called ozone. Ozone blocks most of the harmful ultraviolet rays from reaching Earth's surface. Some ultraviolet rays get through, however. They are responsible for sunburn and can cause skin cancer in people. Tiny amounts of human-made chemicals have caused some of the natural ozone to break down. Many people are concerned that the ozone layer may become too thin, allowing ultraviolet rays to reach the surface and harm people and other living things.
Water vapor, carbon dioxide, methane, and other gases in the atmosphere trap heat from the sun, warming Earth. The heat-trapping quality of these gases causes the greenhouse effect. Without the greenhouse effect of the atmosphere, Earth would probably be too cold for life to exist.
Ocean waters cover most of Earth's surface. This satellite view shows the Indian Ocean, partly bordered by Africa, Asia, and Australia, and below it the Southern Ocean surrounding Antarctica.

Earth and its moon

2010-06-14T22:38:00.000-07:00

Earth has one moon. Pluto also has one moon, while Mercury and Venus have none. All the other planets in our solar system have two or more moons. Earth's moon has a diameter of 2,159 miles (3,474 kilometers) -- about one-fourth of Earth's diameter.
View of Earth and the moon from space. Image credit: NASAThe sun's gravity acts on Earth and the moon as if they were a single body with its center about 1,000 miles (1,600 kilometers) below Earth's surface. This spot is the Earth-moon barycenter. It is the point of balance between the heavy Earth and the lighter moon. The path of the barycenter around the sun is a smooth curve. Earth and the moon circle the barycenter as they orbit the sun. The motion of Earth and moon around the barycenter makes them "wobble" in their path around the

Earth's size and shape

2010-06-14T22:31:00.000-07:00

Most people picture Earth as a ball with the North Pole at the top and the South Pole at the bottom. Earth, other planets, large moons, and stars -- in fact, most objects in space bigger than about 200 miles (320 kilometers) in diameter -- are round because of their gravity. Gravity pulls matter in toward the center of objects. Tiny moons, such as the two moons of Mars, have so little gravity that they do not become round, but remain lumpy instead.
To our bodies, "down" is always the direction gravity is pulling. People everywhere on Earth feel "down" is toward the center of Earth and "up" is toward the sky. People in Spain and in New Zealand are on exactly opposite sides of Earth from each other, but both sense their surroundings as "right side up." Gravity works the same way on other planets and moons.
Earth has a diameter of about 7,900 miles (12,700 kilometers). The diameter of Jupiter, the biggest planet in our solar system, is more than 11 times as large as the diameter of Earth. Image credit: NASA/NSSDCEarth, however, is not perfectly round. Earth's spin causes it to bulge slightly at its middle, the equator. The diameter of Earth from North Pole to South Pole is 7,899.83 miles (12,713.54 kilometers), but through the equator it is 7,926.41 miles (12,756.32 kilometers). This difference, 26.58 miles (42.78 kilometers), is only 1/298 the diameter of Earth. The difference is too tiny to be easily seen in pictures of Earth from space, so the planet appears round.
Earth's bulge also makes the circumference of Earth larger around the equator than around the poles. The circumference around the equator is 24,901.55 miles (40,075.16 kilometers), but around the poles it is only 24,859.82 miles (40,008.00 kilometers). The circumference is actually greatest just south of the equator, so Earth is slightly pear-shaped. Earth also has mountains and valleys, but these features are tiny compared to the total size of Earth, so the planet appears smooth from space.

How Earth moves

2010-06-14T22:29:00.000-07:00

Earth has three motions. It (1) spins like a top around an imaginary line called an axis that runs from the North Pole to the South Pole, (2) it travels around the sun, and (3) it moves through the Milky Way along with the sun and the rest of the solar system.
Earth takes 24 hours to spin completely around on its axis so that the sun is in the same place in the sky. This period is called a solar day. During a solar day, Earth moves a little around its orbit so that it faces the stars a little differently each night. Thus, it only takes 23 hours 56 minutes 4.09 seconds for Earth to spin once so that the stars appear to be in the same place in the sky. This period is called a sidereal day. A sidereal day is shorter than a solar day, so the stars appear to rise about 4 minutes earlier each day.
Earth takes 365 days 6 hours 9 minutes 9.54 seconds to circle the sun. This length of time is called a sidereal year. Because Earth does not spin a whole number of times as it goes around the sun, the calendar gets out of step with the seasons by about 6 hours each year. Every four years, a day is added to bring the calendar back into line with the seasons. These years, called leap years, have 366 days. The extra day is added to the end of February and occurs as February 29.
The distance around Earth's orbit is 584 million miles (940 million kilometers). Earth travels in its orbit at 66,700 miles (107,000 kilometers) an hour, or 18.5 miles (30 kilometers) a second. Earth's orbit lies on an imaginary flat surface around the sun called the orbital plane.
Earth's axis is not straight up and down, but is tilted by about 23 1/2 degrees compared to the orbital plane. This tilt and Earth's motion around the sun causes the change of the seasons. In January, the northern half of Earth tilts away from the sun. Sunlight is spread thinly over the northern half of Earth, and the north experiences winter. At the same time, the sunlight falls intensely on the southern half of Earth, which has summer. By July, Earth has moved to the opposite side of the sun. Now the northern half of Earth tilts toward the sun. Sunlight falls intensely over the northern half of Earth, and the north experiences summer. At the same time, the sunlight falls less intensely on the southern half of Earth, which has winter.
Earth's orbit is not a perfect circle. Earth is slightly closer to the sun in early January (winter in the Northern Hemisphere) and farther away in July. In January, Earth is 91.4 million miles (147.1 million kilometers) from the sun, and in July it is 94.5 million miles (152.1 million kilometers) from the sun. This variation has a far smaller effect than the heating and cooling caused by the tilt of Earth's axis.
Earth and the solar system are part of a vast disk of stars called the Milky Way Galaxy. Just as the moon orbits Earth and planets orbit the sun, the sun and other stars orbit the tightly packed center of the Milky Way. The solar system is about two-fifths of the way from the center of the Milky Way and revolves around the center at about 155 miles (249 kilometers) per second. The solar system makes one complete revolution around the center of the galaxy in about 220 million years.

Earth as a planet

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Earth ranks fifth in size among the nine planets. It has a diameter of about 8,000 miles (13,000 kilometers). Jupiter, the largest planet, is about 11 times larger in diameter than Earth. Pluto, the smallest planet, has a diameter less than one-fifth that of Earth.
Earth, like all the planets in our solar system, travels around the sun in a path called an orbit. Earth is about 93 million miles (150 million kilometers) from the sun. It takes one year for Earth to complete one orbit around the sun. The innermost planet, Mercury, is only about one-third as far from the sun as Earth and circles the sun in only 88 days. Pluto, the outermost planet, is 40 times as far from the sun as Earth and takes 248 Earth years to circle the sun.

Earth

2010-06-14T22:25:00.000-07:00

Earth is a small planet in the vastness of space. It is one of nine planets that travel through space around the sun. The sun is a star -- one of billions of stars that make up a galaxy called the Milky Way. The Milky Way and as many as 100 billion other galaxies make up the universe.
The planet Earth is only a tiny part of the universe, but it is the home of human beings and, in fact, all known life in the universe. Animals, plants, and other organisms live almost everywhere on Earth's surface. They can live on Earth because it is just the right distance from the sun. Most living things need the sun's warmth and light for life. If Earth were too close to the sun, it would be too hot for living things. If Earth were too far from the sun, it would be too cold for anything to live. Living things also must have water to live. Earth has plenty. Water covers most of Earth's surface.
The study of Earth is called geology, and scientists who study Earth are geologists. Geologists study different physical features of Earth to understand how they were formed and how they may have changed over time. Much of Earth, such as the deep interior, cannot be studied directly. Geologists must often study samples of rock and use indirect methods to learn about the planet. Today, geologists can also view and study the entire Earth from space.
This article discusses Earth (Earth as a planet) (Earth's spheres) (Earth's rocks) (Cycles on and in Earth) (Earth's interior) (Earth's crust) (Earth's changing climate) (History of Earth).

Earth's Climatic History

2010-06-14T19:57:00.001-07:00

Climatologists have used various techniques and evidence to reconstruct a history of the Earth's past climate. From this data, they have found that during most of the Earth's history global temperatures were probably 8 to 15 degrees Celsius warmer than today. In the last billion years of climatic history, warmer conditions were broken by glacial periods starting at 925, 800, 680, 450, 330, and 2 million years before present.
The period from 2,000,000 - 14,000 B.P. (before present) is known as the Pleistocene or Ice Age. During this period, large glacial ice sheets covered much of North America, Europe, and Asia for extended periods of time. The extent of the glacier ice during the Pleistocene was not static. The Pleistocene had periods when the glacier retreated (interglacial) because of warmer temperatures and advanced because of colder temperatures (glacial). During the coldest periods of the Ice Age, average global temperatures were probably 4 - 5 degrees Celsius colder than they are today.
The most recent glacial retreat is still going on. We call the temporal period of this retreat the Holocene epoch. This warming of the Earth and subsequent glacial retreat began about 14,000 years ago (12,000 BC). The warming was shortly interrupted by a sudden cooling, known as the Younger-Dryas, at about 10,000 - 8500 BC. Scientists speculate that this cooling may have been caused by the release of fresh water trapped behind ice on North America into the North Atlantic Ocean. The release altered vertical currents in the ocean which exchange heat energy with the atmosphere. The warming resumed by 8500 BC. By 5000 to 3000 BC average global temperatures reached their maximum level during the Holocene and were 1 to 2 degrees Celsius warmer than they are today. Climatologists call this period the Climatic Optimum. During the Climatic Optimum, many of the Earth's great ancient civilizations began and flourished. In Africa, the Nile River had three times its present volume, indicating a much larger tropical region.
From 3000 to 2000 BC a cooling trend occurred. This cooling caused large drops in sea level and the emergence of many islands (Bahamas) and coastal areas that are still above sea level today. A short warming trend took place from 2000 to 1500 BC, followed once again by colder conditions. Colder temperatures from 1500 - 750 BC caused renewed ice growth in continental glaciers and alpine glaciers, and a sea level drop of between 2 to 3 meters below present day levels.
The period from 750 BC - 800 AD saw warming up to 150 BC. Temperatures, however, did not get as warm as the Climatic Optimum. During the time of Roman Empire (150 BC - 300 AD) a cooling began that lasted until about 900 AD. At its height, the cooling caused the Nile River (829 AD) and the Black Sea (800-801 AD) to freeze.
The period 900 - 1200 AD has been called the Little Climatic Optimum. It represents the warmest climate since the Climatic Optimum. During this period, the Vikings established settlements on Greenland and Iceland. The snow line in the Rocky Mountains was about 370 meters above current levels. A period of cool and more extreme weather followed the Little Climatic Optimum. A great drought in the American southwest occurred between 1276 and 1299. There are records of floods, great droughts and extreme seasonal climate fluctuations up to the 1400s.
From 1550 to 1850 AD global temperatures were at their coldest since the beginning of the Holocene. Scientists call this period the Little Ice Age. During the Little Ice Age, the average annual temperature of the Northern Hemisphere was about 1.0 degree Celsius lower than today. During the period 1580 to 1600, the western United States experienced one of its longest and most severe droughts in the last 500 years. Cold weather in Iceland from 1753 and 1759 caused 25% of the population to die from crop failure and famine. Newspapers in New England were calling 1816 the year without a summer.
The period 1850 to present is one of general warming. Figure 7x-1 describes the global temperature trends from 1880 to 2006. This graph shows the yearly temperature anomalies that have occurred from an average global temperature calculated for the period 1951-1980. The graph indicates that the anomolies for the first 60 years of the record were consistently negative. However, beginning in 1935 positive anomolies became more common, and from 1980 to 2006 most of the anomolies were between 0.20 to 0.63 degrees Celsius higher than the normal period (1951-1980) average.

Viewing the Earth

2010-06-14T19:54:00.000-07:00

You can view either a map of the Earth showing the day and night regions at this moment, or view the Earth from the Sun, the Moon, the night side of the Earth, above any location on the planet specified by latitude, longitude and altitude, from a satellite in Earth orbit, or above various cities around the globe.
Images can be generated based on a full-colour image of the Earth by day and night, a topographical map of the Earth, up-to-date weather satellite imagery, or a composite image of cloud cover superimposed on a map of the Earth, a colour composite which shows clouds, land and sea temperatures, and ice, or the global distribution of water vapour. Expert mode allows you additional control over the generation of the image. You can compose a custom request with frequently-used parameters and save it as a hotlist or bookmark item in your browser. Please consult the Details for additional information and answers to frequently-asked questions.

Tyndall Effect

2010-06-14T19:53:00.001-07:00

The first steps towards correctly explaining the colour of the sky were taken by John Tyndall in 1859. He discovered that when light passes through a clear fluid holding small particles in suspension, the shorter blue wavelengths are scattered more strongly than the red. This can be demonstrated by shining a beam of white light through a tank of water with a little milk or soap mixed in. From the side, the beam can be seen by the blue light it scatters; but the light seen directly from the end is reddened after it has passed through the tank. The scattered light can also be shown to be polarised using a filter of polarised light, just as the sky appears a deeper blue through polaroid sun glasses.
This is most correctly called the Tyndall effect, but it is more commonly known to physicists as Rayleigh scattering--after Lord Rayleigh, who studied it in more detail a few years later. He showed that the amount of light scattered is inversely proportional to the fourth power of wavelength for sufficiently small particles. It follows that blue light is scattered more than red light by a factor of (700/400)4 ~= 10.

Blue Haze and Blue Moon

2010-06-14T19:52:00.000-07:00

Clouds and dust haze appear white because they consist of particles larger than the wavelengths of light, which scatter all wavelengths equally (Mie scattering). But sometimes there might be other particles in the air that are much smaller. Some mountainous regions are famous for their blue haze. Aerosols of terpenes from the vegetation react with ozone in the atmosphere to form small particles about 200 nm across, and these particles scatter the blue light. A forest fire or volcanic eruption may occasionally fill the atmosphere with fine particles of 500--800 nm across, being the right size to scatter red light. This gives the opposite to the usual Tyndall effect, and may cause the moon to have a blue tinge since the red light has been scattered out. This is a very rare phenomenon, occurring literally once in a blue moon.

Sunsets

2010-06-14T19:51:00.000-07:00

When the air is clear the sunset will appear yellow, because the light from the sun has passed a long distance through air and some of the blue light has been scattered away. If the air is polluted with small particles, natural or otherwise, the sunset will be more red. Sunsets over the sea may also be orange, due to salt particles in the air, which are effective Tyndall scatterers. The sky around the sun is seen reddened, as well as the light coming directly from the sun. This is because all light is scattered relatively well through small angles--but blue light is then more likely to be scattered twice or more over the greater distances, leaving the yellow, red and orange colours.

Why is the sky blue?

2010-06-14T19:49:00.000-07:00

A clear cloudless day-time sky is blue because molecules in the air scatter blue light from the sun more than they scatter red light. When we look towards the sun at sunset, we see red and orange colours because the blue light has been scattered out and away from the line of sight.
The white light from the sun is a mixture of all colours of the rainbow. This was demonstrated by Isaac Newton, who used a prism to separate the different colours and so form a spectrum. The colours of light are distinguished by their different wavelengths. The visible part of the spectrum ranges from red light with a wavelength of about 720 nm, to violet with a wavelength of about 380 nm, with orange, yellow, green, blue and indigo between. The three different types of colour receptors in the retina of the human eye respond most strongly to red, green and blue wavelengths, giving us our colour vision.

Earth

2010-06-14T19:46:00.000-07:00

Earth is the only planet whose English name does not derive from Greek/Roman mythology. The name derives from Old English and Germanic. There are, of course, hundreds of other names for the planet in other languages. In Roman Mythology, the goddess of the Earth was Tellus - the fertile soil (Greek: Gaia, terra mater - Mother Earth).
It was not until the time of Copernicus (the sixteenth century) that it was understood that the Earth is just another planet.
Mir space station and Earth's limb Earth, of course, can be studied without the aid of spacecraft. Nevertheless it was not until the twentieth century that we had maps of the entire planet. Pictures of the planet taken from space are of considerable importance; for example, they are an enormous help in weather prediction and especially in tracking and predicting hurricanes. And they are extraordinarily beautiful.
The Earth is divided into several layers which have distinct chemical and seismic properties (depths in km): 0- 40 Crust
40- 400 Upper mantle
400- 650 Transition region
650-2700 Lower mantle
2700-2890 D'' layer
2890-5150 Outer core
5150-6378 Inner core The crust varies considerably in thickness, it is thinner under the oceans, thicker under the continents. The inner core and crust are solid; the outer core and mantle layers are plastic or semi-fluid. The various layers are separated by discontinuities which are evident in seismic data; the best known of these is the Mohorovicic discontinuity between the crust and upper mantle.
Most of the mass of the Earth is in the mantle, most of the rest in the core; the part we inhabit is a tiny fraction of the whole (values below x10^24 kilograms): atmosphere = 0.0000051
oceans = 0.0014
crust = 0.026
mantle = 4.043
outer core = 1.835
inner core = 0.09675
The core is probably composed mostly of iron (or nickel/iron) though it is possible that some lighter elements may be present, too. Temperatures at the center of the core may be as high as 7500 K, hotter than the surface of the Sun. The lower mantle is probably mostly silicon, magnesium and oxygen with some iron, calcium and aluminum. The upper mantle is mostly olivene and pyroxene (iron/magnesium silicates), calcium and aluminum. We know most of this only from seismic techniques; samples from the upper mantle arrive at the surface as lava from volcanoes but the majority of the Earth is inaccessible. The crust is primarily quartz (silicon dioxide) and other silicates like feldspar. Taken as a whole, the Earth's chemical composition (by mass) is:

Darwin & Religion

2010-06-14T19:40:00.000-07:00

Darwin & Religion

Teaching evolution can be fraught with difficulty: it is probably the only scientific theory to be rejected on grounds of personal belief. Because of this, it may be that we should move from simply teaching a series of facts and concepts to looking at the development of the theory of evolution, and placing it in its social and historical contexts.
William Cobern, who has written a number of papers on the teaching of evolution, has commented (1994) "Teaching evolution at the secondary level - is very much like Darwin presenting the Origin of Species to a public who historically held a very different view of origins." To meet this challenge, "teachers [should] preface the conceptual study of evolution with a classroom dialogue ... informed with material on the cultural history of Darwinism." He goes on (1995, p. 295), "I do not believe ... that evolution can be taught effectively by ignoring significant metaphysical (i.e. essentially religious) questions. One addresses these issues not by teaching a doctrine, but by looking back historically to the cultural and intellectual milieu of Darwin's day and the great questions over which people struggled."
What follows is an attempt to provide that historical setting, with information on the key players who developed biological and geological thinking and provided the scientific context in which Darwin could have his momentous insight.

Human Evolution

2010-06-14T19:39:00.001-07:00

Humans are a young species, in geological terms. The average "lifespan" of a mammal species, measured by its duration in the fossil record, is around 10 million years. While hominids have followed a separate evolutionary path since their divergence from the ape lineage, around 7 million years ago, our own species (Homo sapiens) is much younger. Fossils classified as archaic H. sapiens appear about 400,000 years ago, and the earliest known modern humans date back only 170,000 years.
Our knowledge of human evolution is changing rapidly, as new fossils are discovered and described every year. Thirty years ago, it was generally accepted that humans and the great apes last shared a common ancestor perhaps 16-20 million years ago, and that the separate human branch was occupied by only a few species, each evolving from the one before. Now we know, through a combination of new fossil finds and molecular biology, that humans and chimpanzees diverged as little as 7 million years ago, and that our own lineage is "bushy", with many different species in existence at the same time.
Our view of our evolutionary past has changed as social attitudes have changed. Darwin was remarkably prescient when he wrote, in 1871 "The Descent of Man", that humans had evolved in Africa and were closely related to the great apes (gorilla, chimpanzee, and orang-utan). But at that time this view was anathema to many, since the majority of people still accepted the concept of special creation.
This is why the first fossil hominid material to be discovered, that of Neandertal Man, attracted even more controversy than the later discoveries of Australopithecus africanus and Homo erectus. Rather than accept the fossil as the remains of a human ancestor, the distinguished German scientist R. Virchow described it as the skeleton of a diseased Cossack cavalryman. And even once the antiquity of the remains was established, many scientists refused to accept that Neandertals could be closely related to modern humans, depicting them instead as brutish and apelike. This interpretation reflected the prevailing prejudices about human ancestry, and was supported by misinterpretation of the remains of the "Old Man of La Chapelle", whose skeleton was warped by arthritis.
Even when the idea that apes and humans shared a common ancestor became more widely accepted, the concept of an African origin was not. The scientist Ernst Haeckel, for example, was convinced that humanity's nearest common ancestor was the orang-utan, and that humans evolved in Asia. Though wrong in this, he was a persuasive writer and many people came to accept his view.
This is why Eugene Dubois sought the "missing link" between humans and apes in Indonesia (then the Dutch East Indies). However, he met with considerable disbelief - and some ridicule - when he named his Solo River fossils Pithecanthropus (now Homo) erectus and described them as belonging to a human ancestor. This rejection reflected the prevailing view that our large brain had evolved while the skeleton was still ape-like, and Dubois' suggestion that the reverse was true was sidelined.
The "large brain first" view received further support when the Piltdown fossils were presented to the world. While we now know that they are fraudulent, at the time (1911) they seemed to demonstrate quite clearly that early humans had a modern cranium atop an ape-like body. And since the Piltdown remains were found in England, they conveniently supported the prevailing idea that modern humans had evolved in Europe, rather than in Africa.
Consequently, when in 1924 Raymond Dart recognised the position of the Taung baby (Australopithecus africanus) on the human family tree, his ideas initially faced considerable opposition. Not until more australopithecine fossils were discovered did his recognition of A. australis as a hominid gain credence. However, it is now accepted that the ancestors of modern humans evolved in Africa and remained there until perhaps 1.5 million years ago, when Homo erectus populations left Africa and moved rapidly across Europe and Asia.
This diaspora was the reverse of a movement that occurred in the late Miocene, when the ancestors of the African apes migrated from Eurasia into Africa. Here they underwent another adaptive radiation, culminating in the divergence of ancestral chimp and hominid populations from their last common ancestor, 7 million years ago.

Human Evolution

2010-06-14T19:39:00.000-07:00

Earth's History & Evolution

2010-06-14T19:35:00.000-07:00

Sometimes science deals with incredibly large numbers, sometimes with great distances still other times with infinitely small particles. In science we must expand our conception of reality all the time. One of the very difficult concepts is the understanding of time. Everyone is conscious of the changes in the physical and biological world; they give us an awareness of time. The daily rhythm, the seasons, physical changes throughout a human lifetime are familiar concepts of time to us. Time is measured by change, but where change occurs over millions of years our own perception of time is on unfamiliar territory. To understand the rhythm of change of our planet and the effects it has on life on Earth we have to expand our perception of time. The geological processes that shape the surface of our planet, move the tectonic plates, build mountains and erode them again work over millions of years. These forces provide the ever changing conditions for life, which adapted to those changes. But those changes did not go undetected. Our understanding of Earth has expanded tremendously in the past 100 years, and new technologies have provided further insight into Earth's dynamic and history.
Earth itself acts like a clock, rotating on its axis once every 24 hours. To read Earth's time it is necessary to look at the changes that have been recorded. To identify changes that occurred due to the geological processes of our planet we can look at rocks. They are key to both the past and the nature of processes. Life has managed to leave records of time and the changes it went through time as well. Fossils are the remains of ancient organisms. Some looked very similar to life forms that are still living today. Fossils can be bones, teeth, shells, impressions of plants and even imprints of animal tracks. Fossils within a rock are a type of organic clock that tick by systematic radioactive decay of certain chemical elements, which permit us to measure with remarkable accuracy the number of years that have passed since the minerals in a rock crystallized. Fossils are recorded in rocks much like your footprints are recorded on a beach. As you walk along the beach, if the sand is fine enough and soft enough, you will make footprints. If the wind and waves do not destroy your footprints, they may record your existence well after your passing.
Fossils are "footprints". Against the odds, these records of past life are preserved. In this section on Earth's history and evolution, we look at the story of Earth's geological and biological history that these "footprints" tell us.

Revising Earth's Early History

2010-06-13T21:19:00.000-07:00

Ordovician Period

2010-06-13T20:36:00.000-07:00

The Ordovician period started at a major extinction event called the Cambrian-Ordovician extinction events some time about 488.3 ± 1.7 Ma [5]. During the Ordovician the southern continents were collected into a single continent called Gondwana. Gondwana started the period in the equatorial latitudes and, as the period progressed, drifted toward the South Pole. Early in the Ordovician the continents Laurentia, Siberia and Baltica were still independent continents (since the break-up of the supercontinent Pannotia earlier), but Baltica began to move toward Laurentia later in the period, causing the Iapetus Ocean to shrink between them. Also, Avalonia broke free from Gondwana and began to head north toward Laurentia. The Rheic Ocean was formed as a result of this. By the end of the period, Gondwana had neared or approached the pole and was largely glaciated.
The Ordovician came to a close in a series of extinction events that, taken together, comprise the second-largest of the five major extinction events in Earth's history in terms of percentage of genera that went extinct. The only larger one was the Permian-Triassic extinction event. The extinctions occurred approximately 444-447 Ma [5] and mark the boundary between the Ordovician and the following Silurian Period.
The most-commonly accepted theory is that these events were triggered by the onset of an ice age, in the Hirnantian faunal stage that ended the long, stable greenhouse conditions typical of the Ordovician. The ice age was probably not as long-lasting as once thought; study of oxygen isotopes in fossil brachiopods shows that it was probably no longer than 0.5 to 1.5 million years.[14] The event was preceded by a fall in atmospheric carbon dioxide (from 7000ppm to 4400ppm) which selectively affected the shallow seas where most organisms lived. As the southern supercontinent Gondwana drifted over the South Pole, ice caps formed on it. Evidence of these ice caps have been detected in Upper Ordovician rock strata of North Africa and then-adjacent northeastern South America, which were south-polar locations at the time.

Paleozoic Era

2010-06-13T20:35:00.000-07:00

The Paleozoic spanned from roughly 542 Ma [5] to roughly 251 Ma [5], and is subdivided into six geologic periods; from oldest to youngest they are the Cambrian, Ordovician, Silurian, Devonian, Carboniferous and Permian. Geologically, the Paleozoic starts shortly after the breakup of a supercontinent called Pannotia and at the end of a global ice age. Throughout the early Palaeozoic, the Earth's landmass was broken up into a substantial number of relatively small continents. Toward the end of the era the continents gathered together into a supercontinent called Pangaea, which included most of the Earth's land area.

Phanerozoic Eon

2010-06-13T20:33:00.000-07:00

The Phanerozoic Eon is the current eon in the geologic timescale. It covers roughly 545 million years. During this period continents drifted about, eventually collected into a single landmass known as Pangea and then split up into the current continental landmasses.
The Phanerozoic is divided into three eras — the Paleozoic, the Mesozoic and the Cenozoic.

Archean Eon

2010-06-13T20:32:00.000-07:00

The Earth of the early Archean (3,800-2,500 Ma) may have had a different tectonic style. During this time, the Earth's crust cooled enough that rocks and continental plates began to form. Some scientists think because the Earth was hotter, that plate tectonic activity was more vigorous than it is today, resulting in a much greater rate of recycling of crustal material. This may have prevented cratonisation and continent formation until the mantle cooled and convection slowed down. Others argue that the subcontinental lithospheric mantle is too buoyant to subduct and that the lack of Archean rocks is a function of erosion and subsequent tectonic events.
In contrast to the Proterozoic, Archean rocks are often heavily-metamorphized deep-water sediments, such as graywackes, mudstones, volcanic sediments and banded iron formations. Greenstone belts are typical Archean formations, consisting of alternating high- and low-grade metamorphic rocks. The high-grade rocks were derived from volcanic island arcs, while the low-grade metamorphic rocks represent deep-sea sediments eroded from the neighboring island arcs and deposited in a forearc basin. In short, greenstone belts represent sutured protocontinents.[9]
By 3.5 billion years ago, the Earth's magnetic field was established. The solar wind flux was about 100 times the value of the modern Sun, so the presence of the magnetic field helped prevent the planet's atmosphere from being stripped away, which is what likely happened to the atmosphere of Mars. However, the field strength was lower than at present and the magnetosphere was about half the modern radius.[10]

Hadean Eon

2010-06-13T20:31:00.002-07:00

During Hadean time (4.6–3.8 Ga), the Solar System was forming, probably within a large cloud of gas and dust around the sun, called an accretion disc. The Hadean Eon isn't formally recognized, but it essentially marks the era before there were any rocks. The oldest dated zircons date from about 4400 Ma (million years ago)[5][8] - very close to the hypothesized time of the Earth's formation.
During the Hadean period the Late Heavy Bombardment occurred (approximately 3800 to 4100 Ma) during which a large number of impact craters are believed to have formed on the Moon, and by inference on Earth, Mercury, Venus and Mars as well.

Precambrian

2010-06-13T20:31:00.001-07:00

Precambrian includes approximately 90% of geologic time. It extends from 4.6 billion years ago to the beginning of the Cambrian Period (about 570 Ma). It includes three eons, the Hadean, Archean, and Proterozoic Eons.

Geological history of Earth

2010-06-13T20:28:00.000-07:00

The geological history of Earth began 4.567 billion years ago[1] when the planets of the Solar System were formed out of the solar nebula, a disk-shaped mass of dust and gas left over from the formation of the Sun. Initially molten, the outer layer of the planet Earth cooled to form a solid crust when water began accumulating in the atmosphere. The Moon formed soon afterwards, possibly as the result of a Mars-sized object with about 10% of the Earth's mass,[2] known as Theia, impacting the Earth in a glancing blow.[3] Some of this object's mass merged with the Earth and a portion was ejected into space, but enough material survived to form an orbiting moon.
Outgassing and volcanic activity produced the primordial atmosphere. Condensing water vapor, augmented by ice delivered by comets, produced the oceans.[4]
As the surface continually reshaped itself over hundreds of millions of years, continents formed and broke up. The continents migrated across the surface, occasionally combining to form a supercontinent. Roughly 750 Ma (million years ago)[5], the earliest-known supercontinent Rodinia, began to break apart. The continents later recombined to form Pannotia, 600–540 Ma,[5] then finally Pangaea, which broke apart 180 Ma [5].[6]
The present pattern of ice ages began about 40 Ma [5], then intensified during the Pleistocene about 3 Ma [5]. The polar regions have since undergone repeated cycles of glaciation and thaw, repeating every 40,000–100,000 years. The last glacial period of the current ice age ended about 10,000 years ago.[7]
The geological history of the Earth can be broadly classified into two periods: the Precambrian supereon and the Phanerozoic eon.

The History of Earth Day

2010-06-13T20:23:00.000-07:00

April 22, 1998 marks the 28th Anniversary of the first Earth Day. Originally called "The First National Environmental Teach-in," Earth Day was modelled after the anti-Vietnam war teach-ins of the late 1960s.
As former Senator Gaylord Nelson recalled in an October 1990 speech: "...[T]he idea for Earth Day occurred to me in late July 1969, while on a conservation speaking tour out West. At the time there was a great deal of turmoil on the college campuses over the Vietnam War. Protests, called anti-war teach-ins, were being widely held on campuses across the nation.. I read an article on the teach-ins, and it suddenly occurred to me, why not have a nationwide teach-in on the environment?

Welcome to earth-history

2010-06-13T20:17:00.000-07:00

1. The pre-publication of a book I started in September 1998 consisting of my theory about Ancient Times.
2. The publication of Ancient texts, especially from the Near East, of which some were gathered from the Internet (with thanks to the publishers) and others from my own library. On this website you can read translations of a lot of ancient texts from Sumer and Babylonia and the Apocrypha, Pseudepigrapha and Sacred texts, most of them I used as a source for my book.

Hadean and Archaean

2010-06-13T20:15:00.000-07:00

Starting with the Earth's formation by accretion from the solar nebula 4.54 billion years ago (4.54 Ga),[1] the first eon in the Earth's history is called the Hadean.[3] It lasted until the Archaean eon, which began 3.8 Ga. The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in some rocks have been dated to about 4.4 Ga,[4] close to the formation of the Earth's crust and the Earth itself. Because not much material from this time is preserved, little is known about Hadean times, but scientists hypothesize at an estimated 4.53 Ga,[nb 1] shortly after formation of an initial crust, the proto-Earth was impacted by a smaller protoplanet, which ejected part of the mantle and crust into space and created the Moon.[6][7][8]
During the Hadean, the Earth's surface was under a continuous bombardment by meteorites, and volcanism must have been severe due to the large heat flow and geothermal gradient. The detrital zircon crystals dated to 4.4 Ga show evidence of having undergone contact with liquid water, considered as proof that the planet already had oceans or seas at that time.[4] From crater counts on other celestial bodies it is inferred that a period of intense meteorite impacts, called the "Late Heavy Bombardment", began about 4.1 Ga, and concluded around 3.8 Ga, at the end of the Hadean.[9]
By the beginning of the Archaean, the Earth had cooled significantly. It would have been impossible for most present day life forms to exist due to the composition of the Archaean atmosphere, which lacked oxygen and an ozone layer. Nevertheless it is believed that primordial life began to evolve by the early Archaean, with some possible fossil finds dated to around 3.5 Ga.[10] Some researchers, however, speculate that life could have begun during the early Hadean, as far back as 4.4 Ga, surviving the possible Late Heavy Bombardment period in hydrothermal vents below the Earth's surface.[

Origin of the solar system

2010-06-13T20:14:00.000-07:00

The Solar System (including the Earth) formed from a large, rotating cloud of interstellar dust and gas called the solar nebula, orbiting the Milky Way's galactic center. It was composed of hydrogen and helium created shortly after the Big Bang 13.7 Ga and heavier elements ejected by supernovas.[12] About 4.6 Ga, the solar nebula began to contract, possibly due to the shock wave of a nearby supernova. Such a shock wave would have also caused the nebula to rotate and gain angular momentum. As the cloud began to accelerate its rotation, gravity and inertia flattened it into a protoplanetary disk oriented perpendicularly to its axis of rotation. Most of the mass concentrated in the middle and began to heat up, but small perturbations due to collisions and the angular momentum of other large debris created the means by which protoplanets up to several kilometres in length began to form, orbiting the nebular center.
The infall of material, increase in rotational speed and the crush of gravity created an enormous amount of kinetic heat at the center. Its inability to transfer that energy away through any other process at a rate capable of relieving the build-up resulted in the disk's center heating up. Ultimately, nuclear fusion of hydrogen into helium began, and eventually, after contraction, a T Tauri star ignited to create the Sun. Meanwhile, as gravity caused matter to condense around the previously perturbed objects outside the gravitational grasp of the new sun, dust particles and the rest of the protoplanetary disk began separating into rings. Successively larger fragments collided with one another and became larger objects, ultimately becoming protoplanets.[13] These included one collection about 150 million kilometers from the center: Earth. The planet formed about 4.54 billion years ago (within an uncertainty of 1%)[1] and was largely completed within 10–20 million years.[14] The solar wind of the newly formed T Tauri star cleared out most of the material in the disk that had not already condensed into larger bodies.
Computer simulations have shown that planets with distances equal to the terrestrial planets in our solar system can be created from a protoplanetary disk.[15] The now widely accepted nebular hypothesis suggests that the same process, which gave rise to the solar system's planets, produces accretion disks around virtually all newly forming stars in the universe, some of which yield planets

Origin of the oceans and atmosphere

2010-06-13T20:12:00.000-07:00

Because the Earth lacked an atmosphere immediately after the giant impact, cooling must have occurred quickly. Within 150 million years, a solid crust with a basaltic composition must have formed. The felsic continental crust of today did not yet exist. Within the Earth, further differentiation could only begin when the mantle had at least partly solidified again. Nevertheless, during the early Archaean (about 3.0 Ga) the mantle was still much hotter than today, probably around 1600°C. This means the fraction of partially molten material was still much larger than today.
Steam escaped from the crust, and more gases were released by volcanoes, completing the second atmosphere. Additional water was imported by bolide collisions, probably from asteroids ejected from the outer asteroid belt under the influence of Jupiter's gravity.
The large amount of water on Earth can never have been produced by volcanism and degassing alone. It is assumed the water was derived from impacting comets that contained ice.[24]:130-132 Though most comets are today in orbits farther away from the Sun than Neptune, computer simulations show they were originally far more common in the inner parts of the solar system. However, most of the water on Earth was probably derived from small impacting protoplanets, objects comparable with today's small icy moons of the outer planets.[25] Impacts of these objects can have enriched the terrestrial planets (Mercury, Venus, the Earth and Mars) with water, carbon dioxide, methane, ammonia, nitrogen and other volatiles. If all water on Earth was derived from comets alone, millions of comet impacts would be required to support this theory. Computer simulations illustrate that this is not an unreasonable number.[24]:131
As the planet cooled, clouds formed. Rain created the oceans. Recent evidence suggests the oceans may have begun forming by 4.2 Ga,[26] or as early as 4.4 Ga.[4] In any event, by the start of the Archaean eon the Earth was already covered with oceans. The new atmosphere probably contained water vapor, carbon dioxide, nitrogen, and smaller amounts of other gases.[27] As the output of the Sun was only 70% of the current amount, significant amounts of greenhouse gas in the atmosphere most likely prevented the surface water from freezing.[28] Free oxygen would have been bound by hydrogen or minerals on the surface. Volcanic activity was intense and, without an ozone layer to hinder its entry, ultraviolet radiation flooded the surface.

The first continents

2010-06-13T20:10:00.000-07:00

Mantle convection, the process that drives plate tectonics today, is a result of heat flow from the core to the Earth's surface. It involves the creation of rigid tectonic plates at mid-oceanic ridges. These plates are destroyed by subduction into the mantle at subduction zones. The inner Earth was warmer during the Hadean and Archaean eons, so convection in the mantle must have been faster. When a process similar to present day plate tectonics did occur, this would have gone faster too. Most geologists believe that during the Hadean and Archaean, subduction zones were more common, and therefore tectonic plates were smaller.
The initial crust, formed when the Earth's surface first solidified, totally disappeared from a combination of this fast Hadean plate tectonics and the intense impacts of the Late Heavy Bombardment. It is, however, assumed that this crust must have been basaltic in composition, like today's oceanic crust, because little crustal differentiation had yet taken place. The first larger pieces of continental crust, which is a product of differentiation of lighter elements during partial melting in the lower crust, appeared at the end of the Hadean, about 4.0 Ga. What is left of these first small continents are called cratons. These pieces of late Hadean and early Archaean crust form the cores around which today's continents grew.
The oldest rocks on Earth are found in the North American craton of Canada. They are tonalites from about 4.0 Ga. They show traces of metamorphism by high temperature, but also sedimentary grains that have been rounded by erosion during transport by water, showing rivers and seas existed then.[24]
Cratons consist primarily of two alternating types of terranes. The first are so called greenstone belts, consisting of low grade metamorphosed sedimentary rocks. These "greenstones" are similar to the sediments today found in oceanic trenches, above subduction zones. For this reason, greenstones are sometimes seen as evidence for subduction during the Archaean. The second type is a complex of felsic magmatic rocks. These rocks are mostly tonalite, trondhjemite or granodiorite, types of rock similar in composition to granite (hence such terranes are called TTG-terranes). TTG-complexes are seen as the relicts of the first continental crust, formed by partial melting in basalt. The alternation between greenstone belts and TTG-complexes is interpreted as a tectonic situation in which small proto-continents were separated by a thorough network of subduction zones.

Origin of life

2010-06-13T20:08:00.000-07:00

The details of the origin of life are unknown, but the basic principles have been established. There are two schools of thought about the origin of life. One suggests that organic components arrived on Earth from space (see “Panspermia”), while the other argues that they originated on Earth. Nevertheless, both schools suggest similar mechanisms by which life initially arose.[29]
If life arose on Earth, the timing of this event is highly speculative—perhaps it arose around 4 Ga.[30] It is possible that, as a result of repeated formation and destruction of oceans during that time period caused by high energy asteroid bombardment, life may have arisen and extinguished more than once.[4]
In the energetic chemistry of early Earth, a molecule gained the ability to make copies of itself — a replicator. (More accurately, it promoted the chemical reactions which produced a copy of itself.) The replication was not always accurate: some copies were slightly different from their parent.
If the change destroyed the copying ability of the molecule, the molecule did not produce any copies, and the line “died out”. On the other hand, a few rare changes might have made the molecule replicate faster or better: those “strains” would become more numerous and “successful”. This is an early example of evolution on abiotic material. The variations present in matter and molecules combined with the universal tendency for systems to move towards a lower energy state allowed for an early method of natural selection. As choice raw materials (“food”) became depleted, strains which could utilize different materials, or perhaps halt the development of other strains and steal their resources, became more numerous.[31]:563-5

Proterozoic eon

2010-06-13T20:07:00.000-07:00

The Proterozoic is the eon of Earth's history that lasted from 2.5 Ga to 542 Ma. In this time span, the cratons grew into continents with modern sizes. For the first time plate tectonics took place in a modern sense. The change to an oxygen-rich atmosphere was a crucial development. Life developed from prokaryotes into eukaryotes and multicellular forms. The Proterozoic saw a couple of severe ice ages called snowball Earths. After the end of the last Snowball Earth about 600 Ma, the evolution of life on Earth accelerated. About 580 Ma, the Ediacara biota formed the prelude for the Cambrian Explosion.

Cambrian explosion

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Apparently, the rate of the evolution of life accelerated in the Cambrian period (542-488 Ma). The sudden emergence of many new species, phyla, and forms in this period is called the Cambrian Explosion. The biological formenting in the Cambrian Explosion was unpreceded before and since that time.[24]:229 Whereas the Ediacaran life forms appear yet primitive and not easy to put in any modern group, at the end of the Cambrian most modern phyla were already present. The development of hard body parts such as shells, skeletons or exoskeletons in animals like molluscs, echinoderms, crinoids and arthropods (a well-known group of arthropods from the lower Paleozoic are the trilobites) made the preservation and fossilisation of such life forms easier than those of their Proterozoic ancestors.[55] For this reason, much more is known about life in and after the Cambrian than about that of older periods. The boundary between the Cambrian and Ordovician (the following period, 488-444 Ma) is characterized by a large mass-extinction, in which some of the new groups disappeared altogether.[56] Some of these Cambrian groups appear complex but are quite different from modern life; examples are Anomalocaris and Haikouichthys.
During the Cambrian, the first vertebrate animals, among them the first fishes, had appeared.[57] A creature that could have been the ancestor of the fishes, or was probably closely related to it, was Pikaia. It had a primitive notochord, a structure that could have developed into a vertebral column later. The first fishes with jaws (Gnathostomata) appeared during the Ordovician. The colonisation of new niches resulted in massive body sizes. In this way, fishes with increasing sizes evolved during the early Paleozoic, such as the titanic placoderm Dunkleosteus, which could grow 7 meters long.

Human evolution

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A small African ape living around six Ma was the last animal whose descendants would include both modern humans and their closest relatives, the bonobo and chimpanzees.[31]:100-101 Only two branches of its family tree have surviving descendants. Very soon after the split, for reasons that are still debated, apes in one branch developed the ability to walk upright.[31]:95-99 Brain size increased rapidly, and by 2 Ma, the first animals classified in the genus Homo had appeared.[63]:300 Of course, the line between different species or even genera is somewhat arbitrary as organisms continuously change over generations. Around the same time, the other branch split into the ancestors of the common chimpanzee and the ancestors of the bonobo as evolution continued simultaneously in all life forms.[31]:100-101
The ability to control fire probably began in Homo erectus (or Homo ergaster), probably at least 790,000 years ago[81] but perhaps as early as 1.5 Ma.[31]:67 In addition, it has sometimes suggested that the use and discovery of controlled fire may even predate Homo erectus. Fire was possibly used by the early Lower Paleolithic (Oldowan) hominid Homo habilis or strong australopithecines such as Paranthropus.[82]
It is more difficult to establish the origin of language; it is unclear whether Homo erectus could speak or if that capability had not begun until Homo sapiens.[31]:67 As brain size increased, babies were born earlier, before their heads grew too large to pass through the pelvis. As a result, they exhibited more plasticity, and thus possessed an increased capacity to learn and required a longer period of dependence. Social skills became more complex, language became more sophisticated, and tools became more elaborate. This contributed to further cooperation and intellectual development.[83]:7 Modern humans (Homo sapiens) are believed to have originated somewhere around 200,000 years ago or earlier in Africa; the oldest fossils date back to around 160,000 years ago.[84]
The first humans to show signs of spirituality are the Neanderthals (usually classified as a separate species with no surviving descendants); they buried their dead, often apparently with food or tools.[85]:17 However, evidence of more sophisticated beliefs, such as the early Cro-Magnon cave paintings (probably with magical or religious significance)[85]:17-19 did not appear until some 32,000 years ago.[86] Cro-Magnons also left behind stone figurines such as Venus of Willendorf, probably also signifying religious belief.[85]:17-19 By 11,000 years ago, Homo sapiens had reached the southern tip of South America, the last of the uninhabited continents (except for Antarctica, which remained undiscovered until 1820 AD).[87] Tool use and communication continued to improve, and interpersonal relationships became more intricate.

Mesozoic

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The most severe extinction event to date took place 250 Ma, at the boundary of the Permian and Triassic periods; 95% of life on Earth died out. That started the Mesozoic era (meaning middle life) that spanned 187 million years,[71] possibly due to the Siberian Traps volcanic event. The discovery of the Wilkes Land crater in Antarctica may indicate a connection with the Permian-Triassic extinction, but the age of that crater is not known.[72] Among other speculative theories, it has been suggested that what is now the Gulf of Mexico was created by a large bolide impact event at that time.[73] Life persevered, and around 230 Ma,[74] dinosaurs split off from their reptilian ancestors. An extinction event between the Triassic and Jurassic periods 200 Ma spared many of the dinosaurs,[75] and they soon became dominant among the vertebrates. Though some of the mammalian lines began to separate during this period, existing mammals were probably all small animals resembling shrews.[31]:169
By 180 Ma, Pangaea broke up into Laurasia and Gondwana. The boundary between avian and non-avian dinosaurs is not clear, but Archaeopteryx, traditionally considered one of the first birds, lived around 150 Ma.[76] The earliest evidence for the angiosperms evolving flowers is during the Cretaceous period, some 20 million years later (132 Ma).[77] Competition with birds drove many pterosaurs to extinction and the dinosaurs were probably already in decline[78] when, 65 Ma, a 10-kilometre (6.2 mi) meteorite probably struck Earth just off the Yucatán Peninsula where the Chicxulub crater is today. This ejected vast quantities of particulate matter and vapor into the air that occluded sunlight, inhibiting photosynthesis. Most large animals, including the non-avian dinosaurs, became extinct,[79] marking the end of the Cretaceous period and Mesozoic era. Thereafter, in the Paleocene epoch, mammals rapidly diversified, grew larger, and became the dominant vertebrates. Perhaps a couple of million years later (around 63 Ma), the last common ancestor of primates lived.[31]:160 By the late Eocene epoch, 34 Ma, some terrestrial mammals had returned to the oceans to become animals such as Basilosaurus which eventually led to dolphins and baleen whales.[80]

Paleozoic tectonics, paleogeography and climate

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At the end of the Proterozoic, the supercontinent Pannotia had broken apart in the smaller continents Laurentia, Baltica, Siberia and Gondwana. During periods when continents move apart, more oceanic crust is formed by volcanic activity. Because young volcanic crust is relatively hotter and less dense than old oceanic crust, the ocean floors will rise during such periods. This causes the sea level to rise. Therefore, in the first half of the Paleozoic, large areas of the continents were below sea level.
Early Paleozoic climates were warmer than today, but the end of the Ordovician saw a short ice age during which glaciers covered the south pole, where the huge continent Gondwana was situated. Traces of glaciation from this period are only found on former Gondwana. During the Late Ordovician ice age, a number of mass extinctions took place, in which many brachiopods, trilobites, Bryozoa and corals disappeared. These marine species could probably not contend with the decreasing temperature of the sea water.[58] After the extinctions new species evolved, more diverse and better adapted. They would fill the niches left by the extinct species.

Civilization

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Vitruvian Man by Leonardo da Vinci epitomizes the advances in art and science seen during the Renaissance.
Throughout more than 90% of its history, Homo sapiens lived in small bands as nomadic hunter-gatherers.[83]:8 As language became more complex, the ability to remember and communicate information resulted in a new replicator: the meme.[88] Ideas could be exchanged quickly and passed down the generations.
Cultural evolution quickly outpaced biological evolution, and history proper began. Somewhere between 8500 and 7000 BC, humans in the Fertile Crescent in Middle East began the systematic husbandry of plants and animals: agriculture.[89] This spread to neighboring regions, and developed independently elsewhere, until most Homo sapiens lived sedentary lives in permanent settlements as farmers.
Not all societies abandoned nomadism, especially those in isolated areas of the globe poor in domesticable plant species, such as Australia.[90] However, among those civilizations that did adopt agriculture, the relative stability and increased productivity provided by farming allowed the population to expand.
Agriculture had a major impact; humans began to affect the environment as never before. Surplus food allowed a priestly or governing class to arise, followed by increasing division of labor. This led to Earth’s first civilization at Sumer in the Middle East, between 4000 and 3000 BC.[83]:15 Additional civilizations quickly arose in ancient Egypt, at the Indus River valley and in China.

THE EARLIEST LIFE

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The very beginning is probably one of the most fascinating parts of the story of life. The oldest fossils are the approximately 3.465 Billion-year-old (Ga) microfossils from the Apex Chert, Australia. These are colonies of cyanobacteria (formerly called blue-green algae) which built real reefs. The oldest stromatolites were found in Australia and are dated 3.45 Ga.

History of the Earth

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The history of the Earth describes the most important events and fundamental stages in the development of the planet Earth from its formation 4.6 billion years ago to the present day.[1] Nearly all branches of natural science have contributed to the understanding of the main events of the Earth's past. The age of Earth is approximately one-third of the age of the universe.[2] Immense geological and biological changes have occurred during that time span.
The oxygen revolution
The first cells were likely heterotrophs, using surrounding organic molecules (including those from other cells) as raw material and an energy source.[31]:564-566 As the food supply diminished, a new strategy evolved in some cells. Instead of relying on the diminishing amounts of free-existing organic molecules, these cells adopted sunlight as an energy source. Estimates vary, but by about 3 Ga, something similar to modern oxygenic photosynthesis had probably developed, which made the sun’s energy available not only to autotrophs but also to the heterotrophs that consumed them.[38][39] This type of photosynthesis, which became by far the most common, used the abundant carbon dioxide and water as raw materials and, with the energy of sunlight, produced energy-rich organic molecules (carbohydrates).
Moreover, oxygen was released as a waste product of the photosynthesis.[37] At first, it became bound up with limestone, iron, and other minerals. There is substantial proof of this in iron-oxide rich layers in geological strata that correspond with this period. The reaction of the minerals with oxygen would have turned the oceans green. When most of the exposed readily reacting minerals were oxidized, oxygen finally began to accumulate in the atmosphere. Though each cell only produced a minute amount of oxygen, the combined metabolism of many cells over a vast time transformed Earth’s atmosphere to its current state.[34]:50-51 Among the oldest examples of oxygen-producing lifeforms are fossil stromatolites. This was Earth’s third atmosphere.

Earth

Common Misconceptions about Evolution

What is Evolution?

Suggested Further Reading

Accumulation of metals into the oceans

Accumulation of meteoritic dust on the Moon

Decay of the Earth's magnetic field

How Old Is The Earth, And How Do We Know?

Earth's electromagnetic field

Earth's interior

Earth science

Physics

Earth science

Chemistry

Biology

Astronomy

History

Overview

Natural science

Natural resources and land use

Weather and climate

Atmosphere

Shape

Composition and structure

Future

21st Century

20th Century

19th Century

Earth History

Our close proximity prevents us from seeing Earth in its entirety

Earth has a magnetic field

Earth has one natural satellite

Earth has an atmosphere that sustains life

Earth has four distinct seasons

Early philosophy had the Earth as the center of the universe

Earth is mostly covered in water

Earth is the only planet known to harbor life

Earth is the fifth largest planet

Earth is the third planet from the Sun

The Environment and World History

Food and the future

Sustainable development

Climate and water

Global water crisis

GM crops: Time to choose

Fossil fuels

Organic farming

Ice Cores

Energy for a cool planet

Earth and environment archive

What is Earth made of?

Earth first anamils

The Mesozoic Era

Life on Earth

History of Earth

Earth's rocks

The atmosphere

Earth and its moon

Earth's size and shape

How Earth moves

Earth as a planet

Earth

Earth's Climatic History

Viewing the Earth

Tyndall Effect

Blue Haze and Blue Moon

Sunsets

Why is the sky blue?

Earth

Darwin & Religion

Human Evolution

Human Evolution

Earth's History & Evolution

Revising Earth's Early History

Ordovician Period

Paleozoic Era

Phanerozoic Eon

Archean Eon

Hadean Eon

Precambrian