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66-581: The Gawler craton and Terre Adélie craton share late Archean and early Proterozoic tectono-thermal events, and may be considered to be a single terrain from the Archean until rifting in the Cretaceous . There are correlatable timelines between the Gawler–Adélie Craton, Curnamona Province and North Australian Craton around 2500–2430 Ma, 2000 Ma, 1865–1850 Ma, 1730–1690 Ma and 1600–1550 Ma. It

132-456: A magma ocean was present, the atmosphere was mainly steam, and surface temperatures reached up to 8,000 K (14,000 °F). Earth's surface then cooled and the atmosphere stabilized, establishing the prebiotic atmosphere. The environmental conditions during this time period were quite different from today: the Sun was ~30% dimmer overall yet brighter at ultraviolet and x-ray wavelengths, there

198-806: A diameter greater than 10 kilometers (6 mi) every 15 million years. This is about the size of the Chicxulub impactor. These impacts would have been an important oxygen sink and would have caused drastic fluctuations of atmospheric oxygen levels. The Archean atmosphere is thought to have almost completely lacked free oxygen ; oxygen levels were less than 0.001% of their present atmospheric level, with some analyses suggesting they were as low as 0.00001% of modern levels. However, transient episodes of heightened oxygen concentrations are known from this eon around 2,980–2,960 Ma, 2,700 Ma, and 2,501 Ma. The pulses of increased oxygenation at 2,700 and 2,501 Ma have both been considered by some as potential start points of

264-413: A feature in later, more oxic oceans. Despite the lack of free oxygen, the rate of organic carbon burial appears to have been roughly the same as in the present. Due to extremely low oxygen levels, sulphate was rare in the Archean ocean, and sulphides were produced primarily through reduction of organically sourced sulphite or through mineralisation of compounds containing reduced sulphur. The Archean ocean

330-408: A few asteroid impacts large enough to vaporize the oceans and melt Earth's surface could have occurred, with smaller impacts expected in even larger numbers. These impacts would have significantly changed the chemistry of the prebiotic atmosphere by heating it up, ejecting some of it to space, and delivering new chemical material. Studies of post-impact atmospheres indicate that they would have caused

396-494: A magma ocean. As the Earth cooled by radiating away the excess energy from the impact, the magma ocean solidified and volatiles were partitioned between the mantle and atmosphere until a stable state was reached. It is estimated that Earth transitioned from the hot, post-impact environment into a potentially habitable environment with crustal recycling, albeit different from modern plate tectonics , roughy 10-20 million years after

462-455: A range of possible constraints on the prebiotic N 2 abundance. For example, a recent modeling study that incorporates atmospheric escape , magma ocean chemistry, and the evolution of Earth's interior chemistry suggests that the atmospheric N 2 abundance was probably less than half of the present day value. However, this study fits into a larger body of work that generally constrains the prebiotic N 2 abundance to be between half and double

528-499: A reduced form (e.g. CH 4 ). In a reducing atmosphere , more species will be in their reduced, generally hydrogen-bearing forms. Because there was very little O 2 in the prebiotic atmosphere, it is generally believed that the prebiotic atmosphere was "weakly reduced" - although some argue that the atmosphere was "strongly reduced". In a weakly reduced atmosphere, reduced gases (e.g. CH 4 and NH 3 ) and oxidized gases (e.g CO 2 ) are both present. The actual H 2 abundance in

594-401: Is a negative feedback loop that modulates Earth's surface temperature by partitioning carbon between the atmosphere and the mantle via several surface processes. It has been proposed that the processes of the carbonate-silicate cycle would result in high CO 2 levels in the prebiotic atmosphere to offset the lower energy input from the faint young Sun. This mechanism can be used to estimate

660-529: Is a lack of extensive geological evidence for specific continents. One hypothesis is that rocks that are now in India, western Australia, and southern Africa formed a continent called Ur as of 3,100 Ma. Another hypothesis, which conflicts with the first, is that rocks from western Australia and southern Africa were assembled in a continent called Vaalbara as far back as 3,600 Ma. Archean rock makes up only about 8% of Earth's present-day continental crust;

726-499: Is an important component of the prebiotic atmosphere because, as a greenhouse gas , it strongly affects the surface temperature; also, it dissolves in water and can change the ocean pH. The abundance of carbon dioxide in the prebiotic atmosphere is not directly constrained by geochemical data and must be inferred. Evidence suggests that the carbonate-silicate cycle regulates Earth's atmospheric carbon dioxide abundance on timescales of about 1 million years. The carbonate-silicate cycle

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792-399: Is determined by the incoming solar flux, the rate of lightning, and the abundances of the other atmospheric gases that take part in the chemical reactions (e.g. CO 2 , H 2 O, OH), as well as their vertical distributions. O 2 is removed from the atmosphere via photochemical reactions that mainly involve H 2 and CO near the surface. The most important of these reactions starts when H 2

858-484: Is evidenced by certain highly deformed gneisses produced by metamorphism of sedimentary protoliths . The moderate temperatures may reflect the presence of greater amounts of greenhouse gases than later in the Earth's history. Extensive abiotic denitrification took place on the Archean Earth, pumping the greenhouse gas nitrous oxide into the atmosphere. Alternatively, Earth's albedo may have been lower at

924-406: Is hypothesized to overlap with the beginning of the Archean. The Huronian glaciation occurred at the end of the eon. The Earth during the Archean was mostly a water world : there was continental crust , but much of it was under an ocean deeper than today's oceans. Except for some rare relict crystals , today's oldest continental crust dates back to the Archean. Much of the geological detail of

990-433: Is split into two H atoms by incoming solar photons. The free H then reacts with O 2 and eventually forms H 2 O, resulting in a net removal of O 2 and a net increase in H 2 O. Models that simulate all of these chemical reactions in a potential prebiotic atmosphere show that an extremely small atmospheric O 2 abundance is likely. In one such model that assumed values for CO 2 and H 2 abundances and sources,

1056-400: Is the breakdown and subsequent chemical reactions of other oxygen containing compounds. Incoming solar photons or lightning can break up CO 2 and H 2 O molecules, freeing oxygen atoms and other radicals (i.e. highly reactive gases in the atmosphere). The free oxygen can then combine into O 2 molecules via several chemical pathways. The rate at which O 2 is created in this process

1122-400: Is the second atmosphere present on Earth before today's biotic, oxygen-rich third atmosphere , and after the first atmosphere (which was mainly water vapor and simple hydrides ) of Earth's formation. The formation of the Earth, roughly 4.5 billion years ago, involved multiple collisions and coalescence of planetary embryos. This was followed by a <100 million year period on Earth where

1188-828: Is therefore plausible that throughout the Paleoproterozoic the Gawler– Adélie Craton and North Australian Craton were joined into a single continental terrain. The Mawson Continent seems to have formed during the Kimban orogeny of around 1730–1690 Ma when the Gawler–Adélie Craton combined with the crust of the Miller Range of the Transantarctic Mountains . Later, around 1600–1550 Ma, the Coompana Block and its Antarctic extension

1254-474: Is truly of biotic origin, so it is still debated. Thus, the prebiotic atmosphere concluded 3.5 billion years ago or earlier, placing it in the early Archean Eon or mid-to-late Hadean Eon. Knowledge of the environmental factors at play on early Earth is required to investigate the prebiotic atmosphere. Much of what we know about the prebiotic environment comes from zircons - crystals of zirconium silicate (ZrSiO 4 ). Zircons are useful because they record

1320-468: Is unknown due to the lack of geochemical data from the time period. Current studies generally indicate that the prebiotic atmosphere was "weakly reduced", with elevated levels of CO 2 , N 2 within a factor of 2 of the modern level, negligible amounts of O 2 , and more hydrogen-bearing gases than the modern Earth (see below). Noble gases and photochemical products of the dominant species were also present in small quantities. Carbon dioxide (CO 2 )

1386-578: The Azoic age . Before the Hadean Eon was recognized, the Archean spanned Earth's early history from its formation about 4,540 million years ago until 2,500 million years ago. Instead of being based on stratigraphy , the beginning and end of the Archean Eon are defined chronometrically . The eon's lower boundary or starting point of 4,031±3 million years ago is officially recognized by

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1452-631: The Great Oxygenation Event , which most scholars consider to have begun in the Palaeoproterozoic ( c.  2.4 Ga ). Furthermore, oases of relatively high oxygen levels existed in some nearshore shallow marine settings by the Mesoarchean. The ocean was broadly reducing and lacked any persistent redoxcline , a water layer between oxygenated and anoxic layers with a strong redox gradient, which would become

1518-478: The International Commission on Stratigraphy , which is the age of the oldest known intact rock formations on Earth. Evidence of rocks from the preceding Hadean Eon are therefore restricted by definition to non-rock and non-terrestrial sources such as individual mineral grains and lunar samples. When the Archean began, the Earth's heat flow was nearly three times as high as it is today, and it

1584-731: The Mesoproterozoic and Neoproterozoic . Archean The Archean Eon ( IPA : / ɑːr ˈ k iː ə n / ar- KEE -ən , also spelled Archaean or Archæan ), in older sources sometimes called the Archaeozoic , is the second of the four geologic eons of Earth 's history , preceded by the Hadean Eon and followed by the Proterozoic . The Archean represents the time period from 4,031 to 2,500 Mya (million years ago). The Late Heavy Bombardment

1650-519: The Archean and become common late in the Archean. Cyanobacteria were instrumental in creating free oxygen in the atmosphere. Further evidence for early life is found in 3.47 billion-year-old baryte , in the Warrawoona Group of Western Australia. This mineral shows sulfur fractionation of as much as 21.1%, which is evidence of sulfate-reducing bacteria that metabolize sulfur-32 more readily than sulfur-34. Evidence of life in

1716-437: The Archean has been destroyed by subsequent activity. The Earth's atmosphere was also vastly different in composition from today's: the prebiotic atmosphere was a reducing atmosphere rich in methane and lacking free oxygen . The earliest known life , mostly represented by shallow-water microbial mats called stromatolites , started in the Archean and remained simple prokaryotes ( archaea and bacteria ) throughout

1782-491: The Archean without leaving any. Fossil steranes , indicative of eukaryotes, have been reported from Archean strata but were shown to derive from contamination with younger organic matter. No fossil evidence has been discovered for ultramicroscopic intracellular replicators such as viruses . Fossilized microbes from terrestrial microbial mats show that life was already established on land 3.22 billion years ago. Prebiotic atmosphere The prebiotic atmosphere

1848-525: The Archean, the conditions necessary to sustain life could not have occurred until the Archean Eon. Life in the Archean was limited to simple single-celled organisms (lacking nuclei), called prokaryotes . In addition to the domain Bacteria , microfossils of the domain Archaea have also been identified. There are no known eukaryotic fossils from the earliest Archean, though they might have evolved during

1914-681: The Gawler-Adélie cratons differ in fundamental ways from the Miller Range and other parts of the East Antarctic Shield . There is evidence that suggests that the Miller Range terrain was accreted to the Gawler–Adélie Craton during the 1730–1690 Ma Kimban–Nimrod Orogeny, with a suture zone that may be at or near the location of the Nimrod Group . Australia and Antarctica separated between 85 Ma and 30 Ma. Tectonics in

1980-470: The Late Hadean is more controversial. In 2015, biogenic carbon was detected in zircons dated to 4.1 billion years ago, but this evidence is preliminary and needs validation. Earth was very hostile to life before 4,300 to 4,200 Ma, and the conclusion is that before the Archean Eon, life as we know it would have been challenged by these environmental conditions. While life could have arisen before

2046-573: The Moon-forming impact, around 4.4 billion years ago. The atmosphere present from this point in Earth's history until the origin of life is referred to as the prebiotic atmosphere. It is unknown when exactly life originated. The oldest direct evidence for life on Earth is around 3.5 billion years old, such as fossil stromatolites from North Pole, Western Australia. Putative evidence of life on Earth from older times (e.g. 3.8 and 4.1 billion years ago ) lacks additional context necessary to claim it

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2112-487: The O 2 volume mixing ratio is calculated to be between 10 and 10 near the surface and up to 10 in the upper atmosphere. The hydrogen abundance in the prebiotic atmosphere can be viewed from the perspective of reduction-oxidation (redox) chemistry . The modern atmosphere is oxidizing, due to the large volume of atmospheric O 2 . In an oxidizing atmosphere, the majority of atoms that form atmospheric compounds (e.g. C) will be in an oxidized form (e.g. CO 2 ) instead of

2178-710: The Southern Terrane of the Shackleton Range during the Paleoproterozoic were similar to that of the Mawson Continent, which may mean that this continent extends over the Eastern Antarctic Shield and includes the Shackleton Range. However, the correlations between the Mawson Continent and Shackleton Range do not prove the Shackleton Range was part of the continent, since there could have been rifting or accretion events during

2244-442: The assembly and destruction of one and perhaps several supercontinents . Evidence from banded iron formations, chert beds, chemical sediments and pillow basalts demonstrates that liquid water was prevalent and deep oceanic basins already existed. Asteroid impacts were frequent in the early Archean. Evidence from spherule layers suggests that impacts continued into the later Archean, at an average rate of about one impactor with

2310-433: The atmosphere at least 3.5 billion years ago and possibly much earlier, which marks the end of the prebiotic atmosphere. Earth is believed to have formed over 4.5 billion years ago by accreting material from the solar nebula . Earth's Moon formed in a collision, the Moon-forming impact, believed to have occurred 30-50 million years after the Earth formed. In this collision, a Mars-sized object named Theia collided with

2376-553: The crystalline remnants of the surviving Archean crust. These include great melt sheets and voluminous plutonic masses of granite , diorite , layered intrusions , anorthosites and monzonites known as sanukitoids . Archean rocks are often heavily metamorphized deep-water sediments, such as graywackes , mudstones , volcanic sediments, and banded iron formations . Volcanic activity was considerably higher than today, with numerous lava eruptions, including unusual types such as komatiite . Carbonate rocks are rare, indicating that

2442-471: The deep oceans of the Archean probably covered the continents entirely. Only at the end of the Archean did the continents likely emerge from the ocean. The emergence of continents towards the end of the Archaean initiated continental weathering that left its mark on the oxygen isotope record by enriching seawater with isotopically light oxygen. Due to recycling and metamorphosis of the Archean crust, there

2508-424: The early Earth environment. These studies indicate that the prebiotic atmosphere likely contained more CO 2 than the modern Earth, had N 2 within a factor of 2 of the modern levels, and had vanishingly low amounts of O 2 . The atmospheric chemistry is believed to have been " weakly reducing ", where reduced gases like CH 4 , NH 3 , and H 2 were present in small quantities. The composition of

2574-411: The enhanced x-ray and ultraviolet radiation from the young Sun. N 2 was also likely important for the synthesis of compounds believed to be critical for the origin of life, such as hydrogen cyanide (HCN) and amino acids derived from HCN. Studies have attempted to constrain the prebiotic atmosphere N 2 abundance with theoretical estimates, models, and geologic data. These studies have resulted in

2640-509: The eon. The earliest photosynthetic processes, especially those by early cyanobacteria , appeared in the mid/late Archean and led to a permanent chemical change in the ocean and the atmosphere after the Archean. The word Archean is derived from the Greek word arkhē ( αρχή ), meaning 'beginning, origin'. The Pre-Cambrian had been believed to be without life (azoic); however, fossils were found in deposits that were judged to belong to

2706-458: The form of N 2 is 78% of Earth's modern atmosphere by volume, making it the most abundant gas. N 2 is generally considered a background gas in the Earth's atmosphere because it is relatively unreactive due to the strength of its triple bond. Despite this, atmospheric N 2 was at least moderately important to the prebiotic environment because it impacts the climate via Rayleigh scattering and it may have been more photochemically active under

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2772-530: The neighboring island arcs and deposited in a forearc basin. Greenstone belts, which include both types of metamorphosed rock, represent sutures between the protocontinents. Plate tectonics likely started vigorously in the Hadean , but slowed down in the Archean. The slowing of plate tectonics was probably due to an increase in the viscosity of the mantle due to outgassing of its water. Plate tectonics likely produced large amounts of continental crust, but

2838-552: The ocean condensed are predicted to last up to tens of millions of years before returning to the background state. The prebiotic atmosphere can supply chemical ingredients and facilitate environmental conditions that contribute to the synthesis of organic compounds involved in the origin of life. For example, potential compounds involved in the origin of life were synthesized in the Miller-Urey experiment . In this experiment, assumptions must be made about what gases were present in

2904-484: The oceans were more acidic, due to dissolved carbon dioxide , than during the Proterozoic. Greenstone belts are typical Archean formations, consisting of alternating units of metamorphosed mafic igneous and sedimentary rocks, including Archean felsic volcanic rocks . The metamorphosed igneous rocks were derived from volcanic island arcs , while the metamorphosed sediments represent deep-sea sediments eroded from

2970-716: The oldest rock formations exposed on the surface of the Earth are Archean. Archean rocks are found in Greenland , Siberia , the Canadian Shield , Montana , Wyoming (exposed parts of the Wyoming Craton ), Minnesota (Minnesota River Valley), the Baltic Shield , the Rhodope Massif , Scotland , India , Brazil , western Australia , and southern Africa . Granitic rocks predominate throughout

3036-459: The other hand, the production and stability of origin of life ingredients in a strongly reduced atmosphere are greatly enhanced, making post-impact atmospheres particularly relevant. It is also proposed that the conditions required for the origin of life could have emerged locally, in a system that is isolated from the atmosphere (e.g. a hydrothermal vent ). However, compounds such as cyanides used to make nucleobases of RNA would be too dilute in

3102-455: The overall reduction in energy coming from the Sun, the early Sun emitted more radiation in the ultraviolet and x-ray regimes than it currently does. This indicates that different photochemical reactions may have dominated early Earth's atmosphere, which has implications for global atmospheric chemistry and the formation of important compounds that could lead to the origin of life. Finally, there

3168-462: The oxidation state of Earth's mantle was likely different at early times, which changes the fluxes of chemical species delivered to the atmosphere from volcanic outgassing. Environmental factors from elsewhere in the solar system also affected prebiotic Earth. The Sun was ~30% dimmer overall around the time the Earth formed. This means greenhouse gases may have been required in higher levels than present day to keep Earth from freezing over. Despite

3234-468: The physical and chemical processes occurring on the prebiotic Earth during their formation and they are especially durable. Most zircons that are dated to the prebiotic time period are found at the Jack Hills formation of Western Australia, but they also occur elsewhere. Geochemical data from several prebiotic zircons show isotopic evidence for chemical change induced by liquid water, indicating that

3300-403: The prebiotic CO 2 abundance, but it is debated and uncertain. Uncertainty is primarily driven by a lack of knowledge about the area of exposed land, early Earth's interior chemistry and structure, the rate of reverse weathering and seafloor weathering, and the increased impactor flux. One extensive modeling study suggests that CO 2 was roughly 20 times higher in the prebiotic atmosphere than

3366-405: The prebiotic atmosphere has been estimated by doing a calculation that takes into account the rate at which H 2 is volcanically outgassed to the surface and the rate at which it escapes to space . One of these recent calculations indicates that the prebiotic atmosphere H 2 abundance was around 400 parts per million, but could have been significantly higher if the source from volcanic outgassing

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3432-476: The prebiotic atmosphere to be strongly reduced for a period of time after a large impact. On average, impactors in the early solar system contained highly reduced minerals (e.g. metallic iron) and were enriched with reduced compounds that readily enter the atmosphere as a gas. In these strongly reduced post-impact atmospheres, there would be significantly higher abundances of reduced gases like CH 4 , HCN, and perhaps NH 3 . Reduced, post-impact atmospheres after

3498-454: The prebiotic atmosphere was likely periodically altered by impactors, which may have temporarily caused the atmosphere to have been "strongly reduced". Constraining the composition of the prebiotic atmosphere is key to understanding the origin of life , as it may facilitate or inhibit certain chemical reactions on Earth's surface believed to be important for the formation of the first living organism. Life on Earth originated and began modifying

3564-498: The prebiotic atmosphere. Proposed important ingredients for the origin of life include (but are not limited to) methane (CH 4 ), ammonia (NH 3 ), phosphate, hydrogen cyanide (HCN), various organics , and various photochemical byproducts. The atmospheric composition will impact the stability and production of these compounds at Earth's surface. For example, the "weakly reduced" prebiotic atmosphere may produce some, but not all, of these ingredients via reactions with lightning. On

3630-484: The prebiotic environment had a liquid ocean and a surface temperature that did not cause it to freeze or boil. It is unknown when exactly the continents emerged above this liquid ocean. This adds uncertainty to the interaction between Earth's prebiotic surface and atmosphere, as the presence of exposed land determines the rate of weathering processes and provides local environments that may be necessary for life to form. However, oceanic islands were likely. Additionally,

3696-427: The preindustrial modern value (280 ppm), which would result in a global average surface temperature around 259 K (6.5 °F) and an ocean pH around 7.9. This is in agreement with other studies, which generally conclude that the prebiotic atmospheric CO 2 abundance was higher than the modern one, although the global surface temperature may still be significantly colder due to the faint young Sun. Nitrogen in

3762-574: The present level. Oxygen in the form of O 2 makes up 21% of Earth's modern atmosphere by volume. Earth's modern atmospheric O 2 is due almost entirely to biology (e.g. it is produced during oxygenic photosynthesis ), so it was not nearly as abundant in the prebiotic atmosphere. This is favorable for the origin of life, as O 2 would oxidize organic compounds needed in the origin of life. The prebiotic atmosphere O 2 abundance can be theoretically calculated with models of atmospheric chemistry. The primary source of O 2 in these models

3828-456: The primitive Earth and the remnants of the collision formed the Moon. The collision likely supplied enough energy to melt most of Earth's mantle and vaporize roughly 20% of it, heating Earth's surface to as high as 8,000 K (~14,000 °F). Earth's surface in the aftermath of the Moon-forming impact was characterized by high temperatures (~2,500 K), an atmosphere made of rock vapor and steam, and

3894-690: The rest of the Archean continents have been recycled. By the Neoarchean , plate tectonic activity may have been similar to that of the modern Earth, although there was a significantly greater occurrence of slab detachment resulting from a hotter mantle, rheologically weaker plates, and increased tensile stresses on subducting plates due to their crustal material metamorphosing from basalt into eclogite as they sank. There are well-preserved sedimentary basins , and evidence of volcanic arcs , intracontinental rifts , continent-continent collisions and widespread globe-spanning orogenic events suggesting

3960-853: The time, due to less land area and cloud cover. The processes that gave rise to life on Earth are not completely understood, but there is substantial evidence that life came into existence either near the end of the Hadean Eon or early in the Archean Eon. The earliest evidence for life on Earth is graphite of biogenic origin found in 3.7 billion–year-old metasedimentary rocks discovered in Western Greenland . The earliest identifiable fossils consist of stromatolites , which are microbial mats formed in shallow water by cyanobacteria . The earliest stromatolites are found in 3.48 billion-year-old sandstone discovered in Western Australia . Stromatolites are found throughout

4026-453: Was a liquid ocean , it is unknown if there were continents but oceanic islands were likely, Earth's interior chemistry (and thus, volcanic activity) was different, and there was a larger flux of impactors (e.g. comets and asteroids ) hitting Earth's surface. Studies have attempted to constrain the composition and nature of the prebiotic atmosphere by analyzing geochemical data and using theoretical models that include our knowledge of

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4092-408: Was a significantly higher flux of objects that impacted Earth - such as comets and asteroids - in the early solar system. These impactors may have been important in the prebiotic atmosphere because they can deliver material to the atmosphere, eject material from the atmosphere, and change the chemical nature of the atmosphere after their arrival. The exact composition of the prebiotic atmosphere

4158-415: Was enhanced or atmospheric escape was less efficient than expected. The abundances of other reduced species in the atmosphere can then be calculated with models of atmospheric chemistry. It has been proposed that the large flux of impactors in the early solar system may have significantly changed the nature of the prebiotic atmosphere. During the time period of the prebiotic atmosphere, it is expected that

4224-511: Was enriched in heavier oxygen isotopes relative to the modern ocean, though δ18O values decreased to levels comparable to those of modern oceans over the course of the later part of the eon as a result of increased continental weathering. Astronomers think that the Sun had about 75–80 percent of its present luminosity, yet temperatures on Earth appear to have been near modern levels only 500 million years after Earth's formation (the faint young Sun paradox ). The presence of liquid water

4290-436: Was joined to the continent. The extent of the Mawson Continent is uncertain since Australia is now widely covered by Neoproterozoic to Phanerozoic rocks and Antarctica is almost entirely covered by ice and snow. The Gawler craton, Terre Adélie craton, Miller Range and Shackleton Range have few tectono-thermal events in common, apart from tectonism around 1700 Ma. Airborne and satellite magnetic geophysical data suggest that

4356-411: Was still twice the current level at the transition from the Archean to the Proterozoic (2,500  Ma ). The extra heat was partly remnant heat from planetary accretion , from the formation of the metallic core , and partly arose from the decay of radioactive elements. As a result, the Earth's mantle was significantly hotter than today. Although a few mineral grains have survived from the Hadean ,

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