Timetable of the Precambrian

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Contents 1 The Earliest Solar System 2 The "Proto-earth Eon" 3 The Hadean Eon 4 Archaean Eon 5 Proterozoic Eon 6 Phanerozoic Eon 7 Etymology of Proterozoic geological period names 8 References 9 See also 10 External links

This is a timeline of geological and relevant astronomical events on Earth before the Cambrian period started. This covers 88% of the duration of the Earth. The dates given are based on the best current scientific evidence and where possible are calibrated from a number of independent sources. To get an understanding of the evidence on which these dates are based, we recommend the reader consult the specific Wikipedia article on the events discussed.

[edit] The Earliest Solar System

Main articles: Formation and evolution of the Solar System and Nebular hypothesis

In the earliest solar system history, sun, planetesimals and the jovian planets were formed in short order. The inner solar system aggregate slower than the outer, so the terrestrial planets were not yet formed, including Earth and Moon.

• circa 4570 Ma: A supernova explosion seeds our galactic neighborhood with heavy elements that will be incorporated into the Earth, and results in a shockwave in a dense region of the Milky Way galaxy. The Ca-Al-rich inclusions, which formed 2 million years before the chondrules^[1], are a key signature of a supernova explosion.
• 4567±3 Ma: Rapid collapse of hydrogen molecular cloud, forming a third generation Population I star, the Sun, in a region of the Galactic Habitable Zone (GHZ), about 25,000 light years from the centre of the Milky Way Galaxy ^[2].
• 4566±2 Ma: A protoplanetary disc (from which Earth eventually forms) emerges around the young Sun, which is in its T Tauri stage.

[edit] The "Proto-earth Eon"

• Circa 4560-4550 Ma: Proto-earth forms at the outer (cooler) edge of the Habitable zone of the Solar System. At this stage the solar constant of the sun was only about 73% of its current value, but liquid water may have existed on the surface of the Proto-earth, probably due to the greenhouse warming of high levels of methane and carbon dioxide present in the atmosphere.

[edit] The Hadean Eon

• 4533 Ma Cryptic Era: Hadean eon, Azoic supra-era, and Cryptic era start. The Earth-Moon system forms, possibly as a result of a glancing collision between Proto-earth and the hypothetical protoplanet Theia (see giant impact hypothesis). The Moon geology Pre-Nectarian period starts. Earth was covered by a magma ocean 200 kilometres deep resulting from the impact energy from this and other planetesimals during the early bombardment phase, and energy released by the planetary core forming. Outgassing from crustal rocks gives Earth a reducing atmosphere of methane, nitrogen, hydrogen, ammonia, and water vapour, with minor amounts of hydrogen sulfide, carbon monoxide, and carbon dioxide, in that order. With further full outgassing over 1000°-1500°K, nitrogen and ammonia become minor constituents, and comparable amounts of methane, carbon monoxide, carbon dioxide, water vapour, and hydrogen are released.

• • 4450 Ma: 100 million years after the Moon formed, the first lunar crust, formed of lunar anorthosite, differentiates from lower magmas. The earliest Earth crust probably forms similarly out of similar material. On Earth the pluvial period starts, in which the Earth's crust cools enough to let oceans form by accumulating rainwater.
  • 4404 Ma: First known mineral, found at Jack Hills in Western Australia. Detrital zircons show presence of a solid crust and liquid water. Latest possible date for a secondary atmosphere to form, produced by the Earth's crust outgassing, reinforced by water and possibly organic molecules delivered by comet impacts and Carbonaceous Chondrites (including type CI shown to be high in a number of amino acids and polycyclic aromatic hydrocarbons (PAH)).
• 4150 Ma: Basin Groups Era unofficial period starts.
  • 4100 Ma: Acasta Gneiss of Canada, first known oldest rock, or aggregate of minerals.
• 3920 Ma: Nectarian Era unofficial period starts.
  • 3920-3850 Ma: Late heavy bombardment of the Moon (and probably of the Earth as well) by bolides and asteroids, produced possibly by the planetary migration of Neptune into the Kuiper belt as a result of orbital resonances between Jupiter and Saturn. (see Formation and evolution of the Solar System)^[3]
• 3850 Ma: Lower Imbrian Era unofficial period starts.
  • 3850 Ma: Greenland apatite shows evidence of ¹²C enrichment, characteristic of the presence of photosyntheitic life^[4].
  • 3850 Ma: First evidence of life: Akilia island graphite off Western Greenland contains evidence of kerogen, of a type consistent with photosynthesis. Azoic supra-era ends.

The beginning of the Hadean eon was certainly a harsh place. It is when the Earth was nothing but a condensed portion of the accretion disk that made up the early Solar System. Over millions of years, this condensed portion started to chunk together by the mutual attraction of gravity, and a primitive proto-Earth was formed. Over a period of hundreds of millions of years, until about 4,100 million years ago, the Earth was quite hot. Convection and subduction churned the surface of the planet, creating a planetwide froth of magma. Heavier elements, like iron, lead, and iridium, sunk deep below the surface of the planet, forming its core. Lighter elements, such as gasses, rose to the top in spectacular outgassing events. The surface of the Earth was composed of silicates, which floated on top of the magma seas. Somewhere around the late-to-middle portion of the Hadean eon, the Earth began to cool and the outlines of the continents form. The atmosphere still lacked oxygen at this point. An important event happened early in the Hadean eon, around 4,533 million years ago. The Earth was significantly smaller then, until it was impacted by a Mars-sized body known as Theia. This impact vaporized a huge portion of the crust, and sent many quadrillions of tons of material out into outer space, which hung around in the form of rings for a few million years, until these rings condensed into the body we now call the Moon.

[edit] Archaean Eon

• 3800 Ma: Eoarchean Era and Archean eon start.
  • 3800 Ma: Oldest Banded Iron Formations found.
• 3600 Ma: Paleoarchean Era starts.
  • 3600 Ma: Possible assembly of the Vaalbara supercontinent
• 3500 Ma: Fossils resembling cyanobacteria, found at Warrawoona, Western Australia.
  • 3460 Ma: Fossils of bacteria in chert.
• 3200 Ma: Mesoarchean Era starts.
  • 3200 Ma - 2600 Ma: Assembly of the Ur supercontinent to cover between 12-16% of the current continental crust.
  • 2900 Ma: Assembly of the Kenorland supercontinent, based upon the core of the Baltic shield, formed at 3100 Ma ago.
• 2800 Ma: Neoarchean Era starts.
  • 2800 Ma: Breakup of the Vaalbara supercontinent
  • 2700 Ma: Biomarkers of cyanobacteria discovered, together with steranes (sterols of cholesterol), associated with membranes of eukaryotes, in shales located beneath Banded Iron Formation hematite beds, in Hamersley Range, Western Australia^[5]
  • 2700 Ma: skewed sulphur isotope ratios found in pyrites shows a small rise in oxygen concentration in the atmosphere^[6]

[edit] Proterozoic Eon

• 2500 Ma: Paleoproterozoic Era, Proterozoic eon, and Siderian period start. Banded iron formations form during this period. Earth's atmosphere starts to become oxygenic.
  • 2500 Ma: Assembly of Arctica out of the Canadian Laurentian Shield and Siberian craton.
  • 2400 Ma: Huronian glaciation starts, probably from oxidation of earlier methane greenhouse gas produced by burial of organic sediments of photosynthesisers.
• 2300 Ma: Rhyacian period starts.
  • 2200 - 1800 Ma: Continental Red Beds found, produced by iron in weathered sandstone being exposed to oxygen.
  • 2200 Ma: Iron content of ancient fossil soils shows an oxygen built up to 5-18% of current levels^[7]
  • 2100 Ma: Huronian glaciation ends.
  • 2100 Ma: Earliest known eukaryote fossils found.
• 2050 Ma: Orosirian period starts. Significant orogeny in most continents.
  • 2023 Ma: Vredefort impact structure forms.
  • 2000 Ma: The minor supercontinent Atlantica forms.
  • 2000 Ma: The Oklo natural nuclear reactor of Gabon produced by uranium precipitating bacteria^[8].
  • 1850 Ma: Sudbury impact structure. Penokean orogeny.
• 1800 Ma: Statherian period starts.
  • 1800 Ma: Supercontinent Columbia forms, one of whose fragments being Nena.
• 1600 Ma: Mesoproterozoic Era and Calymmian period start. Platform covers expand.
  • 1500 Ma: Supercontinent Columbia breaks up
• 1400 Ma: Ectasian period starts. Platform covers expand.
  • 1300 Ma: Grenville orogeny starts.
  • 1200 Ma: Red alga Bangiomorpha pubescens, first known sexually reproducing organism.
• 1200 Ma: Stenian period starts, during which supercontinent Rodinia comes together.
  • 1000 Ma: Grenville orogeny ends.
• 1000 Ma: Neoproterozoic Era and Tonian period starts. First radiation of acritarchs. Rodinia starts to break up.
• 850 Ma: Cryogenian period starts, during which Earth entirely freezes over (Snowball Earth) at least 3 times.
  • 750 Ma: Sturtian glaciation starts. Rodinia splits.
  • 700 Ma: Worm impressions in China.
  • 685 Ma: Varanger glaciation begins.
  • 635 Ma: Varanger glaciation ends.
• 635 Ma: Ediacaran period begins.
  • 600 Ma: Pan-African orogeny. Supercontinent Pannotia forms.
  • 575 Ma: First Ediacaran-type fossils.
  • 560 Ma: Trace fossils, e.g., worm burrows, and small bilaterally symmetrical animals. Earliest arthropods.
  • 555 Ma: The first possible mollusk Kimberella appears.
  • 544 Ma: The small shelly fauna first appears.

[edit] Phanerozoic Eon

• 542 Ma: End of the Precambrian. Phanerozoic eon, Palaeozoic era, and Cambrian period begin.
• 251 Ma: Mesozoic era and Triassic period start.
• 65 Ma: Cenozoic era and Tertiary period start.

[edit] Etymology of Proterozoic geological period names

Period	Started	Root word	Meaning	Reason for name
Siderian	2500 Ma	Greek sidēros	iron	ref. the banded iron formations
Rhyacian	2300 Ma	Gk. rhyax	lava flow	much lava flowed
Orosirian	2050 Ma	Gk. orosira	mountain range	much orogeny in this period's latter half
Statherian	1800 Ma	Gk. statheros	stable, firm	continents became stable cratons
Calymmian	1600 Ma	Gk. calymma	cover	platform covers developed or expanded
Ectasian	1400 Ma	Gk. ectasis	extension	platform covers expanded
Stenian	1200 Ma	Gk. stenos	narrow	much orogeny, which survives as narrow metamorphic belts
Tonian	1000 Ma	Gk. tonas	stretch	The continental crust stretched as Rodinia broke up
Cryogenian	850 Ma	cryogenic	freezing-making	In this period all the Earth froze over
Ediacaran	635 Ma	Ediacara Hills		place in Australia where the Ediacaran biota fossils were found

[edit] References

[edit] See also

• Geologic time scale
• Natural history
• Oldest rock
• Precambrian

[edit] External links

• Exploring Time from Planck Time to the lifespan of the universe

Hadean eon
The Hadean is not formally recognized by the International Commission on Stratigraphy. The following subdivisions represent one proposal that is loosely based on the lunar geologic time scale.
Cryptic	Basin Groups	Nectarian	Lower Imbrian

Archean eon
Eoarchean	Paleoarchean	Mesoarchean	Neoarchean

Proterozoic eon
Paleoproterozoic era				Mesoproterozoic era			Neoproterozoic era
Siderian	Rhyacian	Orosirian	Statherian	Calymmian	Ectasian	Stenian	Tonian	Cryogenian	Ediacaran