View source for History of the Earth

{{Dablink|For the history of modern humans, see [[World history]].}}

[[File:4,030,000,000 Years Acasta Gneiss.jpg|thumb|right|A sample of [[gneiss]] from the Earth's oldest dated rocks (the [[Acasta Gneiss|Acasta River]] area of Canada). This sample has been dated at 4.03 billion years old,<ref name="Bowring">{{cite journal | doi = 10.1007/s004100050465 | title = Priscoan (4.00-4.03 Ga) orthogneisses from northwestern Canada | year = 1999 | author = Bowring, Samuel A. | journal = Contributions to Mineralogy and Petrology | volume = 134 | pages = 3–16 | bibcode=1999CoMP..134....3B | last2 = Williams | first2 = Ian S.| issue = 1 | s2cid = 128376754 }}</ref> though the date has been doubted.<ref name="Wilde">[https://www.newscientist.com/article/dn14818-discovery-of-worlds-oldest-rocks-challenged-.html Discovery of world's oldest rocks challenged]</ref>]]
[[File:Earth formation.jpg|thumb|Artist's idea of [[Hadean]] [[eon]] Earth, when it was too hot for any form of life]]

{{main|Formation and evolution of the Solar System}}

The '''history of the Earth''' describes the most important events and stages in the development of the [[planet]] [[Earth]] from its formation to the present day.

The [[age of the Earth]] is about 4.56 [[billion]] years.<ref name=age>Dalrymple, G. Brent 2004. ''Ancient Earth, ancient skies: the age of Earth and its cosmic surroundings''. Stanford.</ref> Nearly all branches of [[science]] have helped us understand the main events of the Earth's past. There has been constant geological change and biological evolution. The geological time scale (GTS), as defined by international convention, shows the large span of time from the beginning of the Earth to the present. 

The Earth is about one-third the age of the [[universe]]. Earth formed as part of the birth of the [[Solar System]].<ref>{{cite journal
 | author= Manhesa, Gérard| author2= Allègre, Claude J.| author3= Dupréa, Bernard| author4= Hamelin, Bruno
| name-list-style= amp | title=Lead isotope study of basic-ultrabasic layered complexes: Speculations about the age of the earth and primitive mantle characteristics
 | url= https://archive.org/details/sim_earth-and-planetary-science-letters_1980-05_47_3/page/370| journal=Earth and Planetary Science Letters
 | date=1980 | volume=47
 | issue= 3 | pages=370–382
 | doi=10.1016/0012-821X(80)90024-2
 | bibcode=1980E&PSL..47..370M
}}</ref> What eventually became the solar system started as a large, rotating cloud of dust and gas. The Sun was composed of hydrogen and some helium. All the heavier elements were produced by stars long gone. They were picked up by the Sun on its travels in the [[Milky Way]] galaxy.

The earliest undisputed evidence of life on Earth dates at least from 3.5 billion years ago during the [[Eoarchean]] [[era]]. There are microbial mat fossils, such as [[stromatolite]]s, found in 3.48 billion-year-old sandstone discovered in Western Australia.

Other work may push this estimate back even further. The [[Abiogenesis|origin of life]] on Earth was at least 3.77 billion years ago, possibly as early as 4.41 billion years ago.<ref name="NAT-20170301">Staff (20 August 2018). A timescale for the origin and evolution of all of life on Earth. ''Phys.org''. Retrieved 20 August 2018. [https://phys.org/news/2018-08-timescale-evolution-life-earth.html]</ref>

==Hadean==
{{Life timeline}}
===Origin===

The formation of Earth occurred as part of the formation of the [[Solar System]]. It started as a large rotating cloud of dust and gas. This cloud, the solar nebula, was composed of [[hydrogen]] and [[helium]] produced in the [[Big Bang]], as well as heavier [[Chemical element|elements]] produced in [[supernova]]s. Then, about 4.68 billion years ago, the [[solar nebula]] began to contract, rotate and gain [[angular momentum]]. This may have been [[wikt:trigger|triggered]] by a star in the region exploding as a supernova, and sending a shock wave through the solar nebula.

As the cloud rotated, it became a flat [[disc]] [[perpendicular]] to its [[axis of rotation]]. Most of the [[mass]] concentrated in the middle and began to heat up. Meanwhile, the rest of the disc began to break up into rings, with [[gravity]] causing matter to condense around [[dust]] [[particle]]s. Small [[wikt:fragment|fragments]] [[wikt:collide|collided]] to become larger fragments, including one collection about {{convert|150|e6km|abbr=off}} from the center: this would become the Earth. As the Sun condensed and heated, [[nuclear fusion]] started, and the [[solar wind]] cleared out most of the material in the disc which had not yet condensed into larger bodies. The same process is expected to produce accretion disks around virtually all newly forming stars in the universe, some of which yield planets.
* [[Age of the Earth]]
* [[Late Heavy Bombardment]]

===Moon===
{{main|Giant impact hypothesis}}
The Earth's relatively large [[natural satellite]] is the [[Moon]]. <ref>The Earth's Moon is larger relative to its planet than any other satellite in the Solar System. [[Pluto]]'s satellite [[Charon (moon)|Charon]] is relatively larger, but Pluto is considered a [[dwarf planet]].</ref> During the [[Apollo program]], rocks from the Moon's surface were brought to Earth. [[Radiometric dating]] of these rocks has shown the Moon to be 4527 ± 10 million years old, about 30 to 55 million years younger than other bodies in the solar system.<ref>Kleine ''et al.'' 2005. Hf-W chronometry of lunar metals and the age and early differentiation of the Moon. ''Science'' '''310''', 1671–1674.</ref><ref>Halliday A.N. 2006. ''The origin of the Earth; what's new?'' ''Elements'' '''2''' 205-210.</ref> New evidence suggests the Moon formed even later, 4.48±0.02 Ga (billion years ago), or 70–110 mya after the start of the Solar System.<ref>Halliday, Alex N 2008. A young Moon-forming giant impact at 70–110 million years accompanied by late-stage mixing, core formation and degassing of the Earth. ''Philosophical Transactions of the Royal Society''. '''366''', 4163-4181. doi:10.1098/rsta.2008.0209. http://rsta.royalsocietypublishing.org/content/366/1883/4163.full.</ref> Another notable feature is the relatively low density of the Moon, which must mean it does not have a large metallic core, like all other [[Terrestrial planet|terrestrial bodies]] in the solar system. 

Theories for the formation of the Moon must explain its late formation as well as the following facts. First, the Moon has a low density (3.3 times that of water, compared to 5.5 for the Earth) and a small metallic core. Second, there is virtually no water or other volatiles on the Moon. Third, the Earth and Moon have the same oxygen isotopic signature (relative abundance of the [[oxygen]] [[isotopes]]). The Moon has a bulk composition closely resembling the Earth's mantle and crust together, without the [[Earth's core]]. This has led to the giant impact hypothesis: the idea that the Moon was formed by a giant impact of the proto-Earth with another protoplanet.<ref>Ida S. Canup R.M. & Stewart G.M. 1997. Lunar accretion from an impact-generated disk, ''Nature'' '''389''', 353-357.</ref>

The impactor, sometimes named [[Theia (planet)|Theia]], is thought to have been a little smaller than the current planet [[Mars]]. Theia finally collided with Earth about 4.533 Ga.<ref>Münker, Carsten ''et al.'' 2003. Evolution of planetary cores and the Earth-Moon system from Nb/Ta systematics. ''Science'' '''301''' (5629): 84–87. doi:10.1126/science.1084662. PMID 12843390. http://sciencemag.org/cgi/content/abstract/301/5629/84 {{Webarchive|url=https://web.archive.org/web/20050913123809/http://www.sciencemag.org/cgi/content/abstract/301/5629/84 |date=2005-09-13 }}.</ref>
Models reveal that when an impactor this size struck the proto-Earth at a low angle and relatively low speed ({{cvt|8|-|20|km/s|disp=or|lk=on}}), much material from the mantles (and proto-crusts) of the proto-Earth and the impactor was ejected into space, where much of it stayed in orbit around the Earth. This material would eventually form the Moon. However, the metallic cores of the impactor would have sunk through the Earth's mantle to fuse with the Earth's core, depleting the Moon of metallic material.<ref>Liu L-G. 1992. Chemical composition of the Earth after the giant impact. ''Earth, Moon, and Planets'' '''57''', 85-97.</ref> The giant impact hypothesis thus explains the Moon's abnormal composition.<ref>Newsom H.E. & Taylor S.R. 1989. Geochemical implications of the formation of the Moon by a single giant impact. ''Nature'' '''338''', 29-34.</ref> The ejecta in orbit around the Earth could have condensed into a single body within a couple of weeks. Under the influence of its own gravity, the ejected material became a more spherical body: the Moon.

The radiometric ages show the Earth existed already for at least 10 million years before the impact, enough time to allow for differentiation of the Earth's primitive mantle and core. Then, when the impact occurred, only material from the mantle was ejected, leaving the Earth's core of heavy elements untouched.

The impact had some important consequences for the young Earth. It released an enormous amount of energy, causing both the Earth and Moon to be completely molten. Immediately after the impact, the Earth's mantle was vigorously [[convection|convecting]], the surface was a large [[magma]] ocean. The planet's first atmosphere must have been completely blown away by the enormous amount of energy released.<ref>Benz W. & Cameron A.G.W. 1990. Terrestrial effects of the giant impact. ''LPI Conference on the Origin of the Earth'', 61-67.</ref> The impact is also thought to have changed Earth’s axis to produce the large 23.5° [[axial tilt]] that is responsible for Earth’s seasons (a simple, ideal model of the planets’ origins would have axial tilts of 0° with no recognizable seasons). It may also have sped up Earth’s rotation.

==Archean==
===Archean Earth===
At the beginning of the Archean, the Earth's heat flow was nearly three times higher than it is today, and was still twice the current level by the beginning of the Proterozoic.  Thus, plates  and [[volcano|volcanic]] activity were considerably more active than they are today; the Earth's crust was not only thinner than is today, but probably broken up into many more [[tectonic plate]]s, with numerous [[Hotspot (geology)|hot spots]], [[Rift (geology)|rift]] [[valley]]s, and [[transform fault]]s. The existence of plate tectonics in this eon is disputed: it is an active area of modern research.<ref name="Stanley">Stanley S.M. 2008. ''Earth system history''. Freeman, San Francisco.</ref><sup>p297-302</sup>

There were no large continents until late in the Archean; small '''protocontinents''' were the norm, prevented from coalescing into larger units by the high rate of geologic activity.  These [[felsic]] protocontinents probably formed at hot spots rather than [[subduction]] zones, from a variety of sources:  [[mafic]] magma melting more felsic rocks, [[magma|partial melting]] of mafic rock, and from the [[metamorphic rock|metamorphic]] alteration of felsic sedimentary rocks.<ref name="Stanley"/><sup>p297-301</sup>

The Archean atmosphere apparently lacked free [[oxygen]]. Temperatures appear to have been near modern levels, although astronomers think that the sun was about one-third dimmer. This suggests larger amounts of greenhouse gases than later in Earth history.

===Archean geology===
[[File:North america terrain 2003 map.jpg|thumb|280px|Geologic map of North America, color-coded by age. The reds and pinks indicate rock from the [[Archean]]. |alt=Map with color and texture]]

When the Archean began, the Earth's heat flow was nearly three times as high as it is today, and it was still twice the current level at the transition from the Archean to the [[Proterozoic]] (2,500 Ma). The extra heat was the result of a mix of remnant heat from planetary accretion, from the formation of the metallic core, and from the decay of radioactive elements.

The oldest rock formations exposed on the surface of the [[Earth]] are Archean or slightly older. Archean rocks are known from [[Greenland]], the [[Canadian Shield]], western [[Australia]], and southern [[Africa]].  Although the first [[continents]] formed during this eon, rock this age makes up only 7% of the world's current [[craton]]s; even allowing for [[erosion]] and destruction of past formations, evidence suggests that only 5-40% of the present [[continental crust]] formed during the Archean.<ref name="Stanley"/><sup>p301</sup>

In contrast to the Proterozoic, Archean rocks are often heavily metamorphized deep-water sediments, such as [[greywacke]]s, [[mudstone]]s, volcanic sediments, and [[banded iron formation]]s. [[Greenstone belt]]s are typical Archean formations: they are made of alternating high and low-grade metamorphic rocks.  The high-grade rocks come from volcanic [[island arc]]s, and the low-grade metamorphic rocks come from deep-sea sediments. These sediments eroded from the island arcs and ended in a [[basin (geology)|forearc basin]].  In short, ''greenstone belts show where protocontinents were stuck together''.<ref name="Stanley"/><sup>p302-3</sup>

===Archean life===
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. Fossils of [[cyanobacteria]]l mats ([[stromatolites]]) are found throughout the Archean—becoming especially common late in the eon—while a few other probable [[bacterium|bacterial]] fossils are known from [[chert]] beds.<ref name="Stanley"/><sup>p307</sup> In addition to [[bacteria]], microfossils of the extremophilic [[archaea]] have also been identified.

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 [[eukaryote]] fossils.<ref name="Stanley"/><sup>p306, 323</sup> No fossil evidence yet exists for [[virus]]es. Fossilized microbes from terrestrial microbial mats show that life was already established on land 3.22 billion years ago.

==Proterozoic==
===The Proterozoic record===
The geologic record of the [[Proterozoic]] is much better than that for the preceding [[Archaean]].  In contrast to the deep-water deposits of the Archean, the Proterozoic features many [[strata]] that were laid down in extensive, shallow epicontinental seas; furthermore, many of these rocks are less [[Metamorphic rock|metamorphosed]] than Archean-age ones, and plenty are in fact unaltered.<ref name="Stanley"/><sup>p315</sup> Study of these rocks show that the eon featured rapid [[continent]]al accretion (unique to the Proterozoic), [[supercontinent]] cycles, and mountain-building ([[orogeny]]) activity.<ref name="Stanley"/><sup>p315/8; 329/32</sup>

The first known [[glaciation]]s occurred during the Proterozoic. One [[ice age]] began shortly after the beginning of the eon. There were at least four during the [[Neoproterozoic]], climaxing with the "[[Snowball Earth]]" of the Varangian glaciation.<ref name="Stanley"/><sup>p320; 325</sup>

=== The build-up of oxygen ===
The [[Great Oxygenation Event]] was one of the most important events of the Proterozoic.  Though oxygen was undoubtedly released by [[photosynthesis]] well back in Archean times, it could not build up to any significant degree until chemical sinks--[[Oxidation|unoxidized]] [[sulfur]] and [[iron]]—had been filled; until roughly 2.3 billion years ago, oxygen was probably only 1 to 2% of its current level.(Stanley, 323)  [[Banded iron formation]]s, which provide most of the world's iron ore, were also a prominent chemical sink; most accumulation ceased after 1.9 billion years ago, either due to an increase in oxygen or a more thorough mixing of the oceanic water column.<ref name="Stanley"/><sup>p324</sup>

[[Red beds]], which are coloured by [[haematite]], indicate an increase in atmospheric oxygen after 2 billion years ago; they are not found in older rocks.(Stanley, 324)  The oxygen build-up was probably due to two factors:  a filling of the chemical sinks, and an increase in [[carbon]] burial, which stored [[Organic chemistry|organic]] compounds which would have otherwise been oxidized by the atmosphere.<ref name="Stanley"/><sup>p325</sup>

===Proterozoic life===
The first advanced single-celled and multi-cellular life roughly coincides with the oxygen accumulation; this may have been due to an increase in the oxidized [[nitrate]]s that [[eukaryote]]s use, as opposed to [[cyanobacteria]].(Stanley, 325)  It was also during the Proterozoic that the first [[symbiosis|symbiotic]] relationship between [[mitochondria]] (for [[animals]] and [[protist]]s) and [[chloroplast]]s (for plants) and their hosts evolved.<ref name="Stanley"/><sup>p321-2</sup>

Eukaryotes such as [[acritarch]]s blossomed, as did cyanobacteria; in fact, [[stromatolite]]s reached their greatest abundance and diversity during the Proterozoic, peaking roughly 1.2 billion years ago.<ref name="Stanley"/><sup>321-3</sup>

Classically, the boundary between the Proterozoic and the [[Paleozoic]] was set at the base of the [[Cambrian]] [[period (geology)|period]] when the first fossils of animals known as [[trilobita|trilobites]] appeared. In the second half of the 20th century, a number of fossil forms have been found in Proterozoic rocks, but the boundary of the Proterozoic is still fixed at the base of the [[Cambrian]]: that is 542 [[mya]].

==Phanerozoic==
===Paleozoic===
The [[Paleozoic]] covers the time from the first appearance of abundant, hard-shelled [[fossil]]s to the time when the [[continent]]s were beginning to be dominated by large, relatively sophisticated [[reptile]]s and relatively modern [[plant]]s. The Paleozoic is a time in Earth's history when complex life forms evolved, took their first breath of [[oxygen]] on dry land, and when the forerunners of all multicelular life on Earth began to diversify. There are six periods in the [[Paleozoic]] [[era]]: [[Cambrian]], [[Ordovician]], [[Silurian]], [[Devonian]], [[Carboniferous]] and [[Permian]].

The upper (youngest) boundary is set at a major [[extinction event]] 250 million years later, known as the [[Permian–Triassic extinction event]]. Modern practice sets the older boundary at the first appearance of a distinctive [[trace fossil]] called ''Phycodes pedum''.

Geologically, the Paleozoic starts shortly after the breakup of a [[supercontinent]] called [[Rodinia]] and at the end of a global [[ice age]] ([[Snowball Earth]]). 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.

At the start of the era, life was confined to [[bacteria]], [[algae]], [[sponge]]s and a variety of somewhat enigmatic forms known collectively as the [[Ediacaran]] [[fauna]]. A large number of body plans appeared nearly simultaneously at the start of the era—a phenomenon known as the [[Cambrian|Cambrian Explosion]].

There is some evidence that simple life may already have invaded the land at the start of the Palaeozoic, but substantial plants and animals did not take to the land until the [[Silurian]] and did not thrive until the [[Devonian]]. Although primitive [[vertebrate]]s are known near the start of the Palaeozoic, animal forms were dominated by [[invertebrate]]s until the mid-Palaeozoic. [[Fish]] populations exploded in the Devonian. During the late Palaeozoic, great [[forest]]s of primitive plants thrived on land forming the great [[coal]] beds of [[Europe]] and eastern [[North America]]. By the end of the era, the first large, sophisticated reptiles and the first modern plants ([[conifer]]s) had developed.

=== Mesozoic ===
The Mesozoic covers the time when life was dominated by large sophisticated [[reptile]]s.  The lower (oldest) boundary is set by the [[P/Tr extinction event]]. The upper (youngest) boundary is set at the [[K/T extinction event]].

Geologically, the Mesozoic starts with almost all the Earth's land collected into a supercontinent called [[Pangaea]]. During the era, Pangaea split into the northern continent [[Laurasia]] and the southern continent [[Gondwana]]. Laurasia then split into North America and Eurasia. Gondwana broke up progressively into continents: [[South America]], [[Africa]], [[Madagascar]], [[India]], [[Australia]] and [[Antarctica]].

The Mesozoic is known as the Age of [[Dinosaur]]s. It also saw the development of early [[bird]]s and [[mammal]]s and, later, flowering [[plant]]s ([[angiosperm]]s). At the end of the Mesozoic, all the major body plans of modern life were in place, though in some cases {{ndash}} notably the mammals {{ndash}} the forms that existed at the end of the [[Cretaceous]] were relatively primitive.

=== Cenozoic ===
The [[Cainozoic|Cenozoic]] is the '''age of [[mammal]]s'''. During the Cenozoic, mammals diverged from a few small, simple, generalized forms into a diverse collection of terrestrial, marine, and flying animals. [[Angiosperms|Flowering plants]] and birds also evolved substantially in the Cenozoic .

[[Geology|Geologically]], the Cenozoic is the [[era]] when [[continent]]s moved into their current positions. [[Africa]] and [[Australasia]] split from [[Gondwana]] to drift north, and [[India]] collided with [[Southeast Asia]]; [[Antarctica]] moved into its current position over the [[South Pole]]; the [[Atlantic Ocean]] widened and, late in the era, [[South America]] became attached to North America.

[[File:Geologic Clock with events and periods.svg|650px|thumb|center|Earth's history with time-spans of the [[Geologic time scale|eon]]s to scale]]

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{{LifeOnEarth}}
{{LocationOfEarth}}

== Related pages ==
{{div col|colwidth=30em}}
* [[Earliest known life forms]]
* [[Earth phase]]
* [[Historical geology]]
* [[Template:Human timeline|Human timeline]]
* [[Template:Nature timeline|Nature timeline]]
* [[Spaceship Earth]]
* ''[[The Blue Marble]]''
{{div col end}}

== References ==
{{Reflist}}

==Other websites==
* [https://nightsky.jpl.nasa.gov/docs/HowFast.pdf Earth&nbsp;– Speed through space&nbsp;– about 1 million miles an hour<!---between 0.8 - 1.9 M mph--->] [[NASA]]. ("[[w:Wikipedia:Reference desk/Archives/Science/2019 July 20#How fast are we moving through space?|WP discussion]]")

== Other sources ==
*New Scientist Essential Guide #17: ''Planet Earth: the incredible story of our unique home''. Published in 2023, and full of interesting ideas.


[[Category:Earth]]
[[Category:Moon]]
[[Category:Earth sciences]]