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The Precambrian
Precambrian
(or Pre-Cambrian, sometimes abbreviated pЄ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic
Phanerozoic
Eon. The Precambrian
Precambrian
is so named because it preceded the Cambrian, the first period of the Phanerozoic
Phanerozoic
eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian
Precambrian
accounts for 88% of the Earth's geologic time. The Precambrian
Precambrian
(colored green in the timeline figure) is a supereon that is subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago (Ga) to the beginning of the Cambrian
Cambrian
Period, about 541 million years ago (Ma), when hard-shelled creatures first appeared in abundance.

Contents

1 Overview 2 Life forms 3 Planetary environment and the oxygen catastrophe 4 Subdivisions 5 Precambrian
Precambrian
supercontinents 6 See also 7 References 8 Further reading 9 External links

Overview[edit] Relatively little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what is known has largely been discovered from the 1960s onwards. The Precambrian
Precambrian
fossil record is poorer than that of the succeeding Phanerozoic, and fossils from the Precambrian
Precambrian
(e.g. stromatolites) are of limited biostratigraphic use.[1] This is because many Precambrian
Precambrian
rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.[1][2][3] It is thought that the Earth coalesced from material in orbit around the Sun at roughly 4,543 Ma, and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that formed the Moon
Moon
(see Giant impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia
Western Australia
have been dated at 4,404 ± 8 Ma.[4] The term "Precambrian" is recognized by the International Commission on Stratigraphy as the only "supereon" in geologic time; it is so called because it includes the Hadean
Hadean
(~4.6—4 billion), Archean (4—2.5 billion), and Proterozoic
Proterozoic
(2.5 billion—541 million) eons. (There is only one other eon: the Phanerozoic, 541 million-present.)[5] "Precambrian" is still used by geologists and paleontologists for general discussions not requiring the more specific eon names. Life forms[edit] Further information: Origin of life

Landmass positions near the end of the Precambrian

A specific date for the origin of life has not been determined. Carbon found in 3.8-billion-year-old rocks ( Archean
Archean
eon) from islands off western Greenland
Greenland
may be of organic origin. Well-preserved microscopic fossils of bacteria older than 3.46 billion years have been found in Western Australia.[6] Probable fossils 100 million years older have been found in the same area. There is a fairly solid record of bacterial life throughout the remainder ( Proterozoic
Proterozoic
eon) of the Precambrian. Excluding a few contested reports of much older forms from North America and India, the first complex multicellular life forms seem to have appeared at roughly 1500 Ma, in the Neoproterozoic era of the Proterozoic
Proterozoic
eon. The oldest fossil evidence from that era of such complex life comes from the Lantian formation of the Ediacarian period, at least 580 million years ago. A very diverse collection of soft-bodied forms is found in a variety of locations worldwide and date to between 635 and 542 Ma. These are referred to as Ediacaran
Ediacaran
or Vendian biota. Hard-shelled creatures appeared toward the end of that time span, marking the beginning of the Phanerozoic
Phanerozoic
eon. By the middle of the following Cambrian
Cambrian
period, a very diverse fauna is recorded in the Burgess Shale, including some which may represent stem groups of modern taxa. The increase in diversity of lifeforms during the early Cambrian
Cambrian
is called the Cambrian
Cambrian
explosion of life.[7][8] While land seems to have been devoid of plants and animals, cyanobacteria and other microbes formed prokaryotic mats that covered terrestrial areas.[9] Planetary environment and the oxygen catastrophe[edit]

Weathered Precambrian
Precambrian
pillow lava in the Temagami Greenstone Belt
Temagami Greenstone Belt
of the Canadian Shield

Evidence of the details of plate motions and other tectonic activity in the Precambrian
Precambrian
has been poorly preserved. It is generally believed that small proto-continents existed prior to 4280 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1130 Ma. The supercontinent, known as Rodinia, broke up around 750 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, roughly 2400–2100 Ma. One of the best studied is the Sturtian-Varangian glaciation, around 850–635 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "Snowball Earth". The atmosphere of the early Earth is not well understood. Most geologists believe it was composed primarily of nitrogen, carbon dioxide, and other relatively inert gases, and was lacking in free oxygen. There is, however, evidence that an oxygen-rich atmosphere existed since the early Archean.[10] At present, it is still believed that molecular oxygen was not a significant fraction of Earth's atmosphere
Earth's atmosphere
until after photosynthetic life forms evolved and began to produce it in large quantities as a byproduct of their metabolism. This radical shift from a chemically inert to an oxidizing atmosphere caused an ecological crisis, sometimes called the oxygen catastrophe. At first, oxygen would have quickly combined with other elements in Earth's crust, primarily iron, removing it from the atmosphere. After the supply of oxidizable surfaces ran out, oxygen would have begun to accumulate in the atmosphere, and the modern high-oxygen atmosphere would have developed. Evidence for this lies in older rocks that contain massive banded iron formations that were laid down as iron oxides. Subdivisions[edit] Main article: Timetable of the Precambrian

Life timeline

view • discuss • edit

-4500 — – -4000 — – -3500 — – -3000 — – -2500 — – -2000 — – -1500 — – -1000 — – -500 — – 0 —

water

Single-celled life

photosynthesis

Eukaryotes

Multicellular life

Land life

Dinosaurs    

Mammals

Flowers

 

Earliest Earth (−4540)

Earliest water

Earliest life

LHB meteorites

Earliest oxygen

Atmospheric oxygen

Oxygen
Oxygen
crisis

Earliest sexual reproduction

Ediacara biota

Cambrian
Cambrian
explosion

Earliest humans

P h a n e r o z o i c

P r o t e r o z o i c

A r c h e a n

H a d e a n

Pongola

Huronian

Cryogenian

Andean

Karoo

Quaternary

Axis scale: million years Orange labels: ice ages. Also see: Human
Human
timeline and Nature timeline

A terminology has evolved covering the early years of the Earth's existence, as radiometric dating has allowed real dates to be assigned to specific formations and features.[11] The Precambrian
Precambrian
Supereon is divided into three eons: the Hadean
Hadean
(4600–4000 Ma), Archean (4000-2500 Ma) and Proterozoic
Proterozoic
(2500-541 Ma). See Timetable of the Precambrian.

Proterozoic: this eon refers to the time from the lower Cambrian boundary, 541 Ma, back through 2500 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian
Cambrian
boundary. The Proterozoic
Proterozoic
eon is divided into three eras: the Neoproterozoic, Mesoproterozoic and Paleoproterozoic.

Neoproterozoic: The youngest geologic era of the Proterozoic
Proterozoic
Eon, from the Cambrian
Cambrian
Period lower boundary (541 Ma) back to 1000 Ma. The Neoproterozoic corresponds to Precambrian
Precambrian
Z rocks of older North American geology.

Ediacaran: The youngest geologic period within the Neoproterozoic Era. The "2012 Geologic Time Scale" dates it from 541 to 635 Ma. In this period the Ediacaran
Ediacaran
fauna appeared. Cryogenian: The middle period in the Neoproterozoic Era: 635-720 Ma. Tonian: the earliest period of the Neoproterozoic Era: 720-1000 Ma.

Mesoproterozoic: the middle era of the Proterozoic
Proterozoic
Eon, 1000-1600 Ma. Corresponds to " Precambrian
Precambrian
Y" rocks of older North American geology. Paleoproterozoic: oldest era of the Proterozoic
Proterozoic
Eon, 1600-2500 Ma. Corresponds to " Precambrian
Precambrian
X" rocks of older North American geology.

Archean
Archean
Eon: 2500-4000 Ma. Hadean
Hadean
Eon: 4000–4600 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean
Hadean
Eon. Other records from Hadean
Hadean
time come from the moon and meteorites.[12]

It has been proposed that the Precambrian
Precambrian
should be divided into eons and eras that reflect stages of planetary evolution, rather than the current scheme based upon numerical ages. Such a system could rely on events in the stratigraphic record and be demarcated by GSSPs. The Precambrian
Precambrian
could be divided into five "natural" eons, characterized as follows:[13]

Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event. Hadean: dominated by heavy bombardment from about 4.51 Ga (possibly including a Cool Early Earth period) to the end of the Late Heavy Bombardment period. Archean: a period defined by the first crustal formations (the Isua greenstone belt) until the deposition of banded iron formations due to increasing atmospheric oxygen content. Transition: a period of continued iron banded formation until the first continental red beds. Proterozoic: a period of modern plate tectonics until the first animals.

Precambrian
Precambrian
supercontinents[edit] The movement of Earth's plates has caused the formation and break-up of continents over time, including occasional formation of a supercontinent containing most or all of the landmass. The earliest known supercontinent was Vaalbara. It formed from proto-continents and was a supercontinent 3.636 billion years ago. Vaalbara
Vaalbara
broke up c. 2.845–2.803 Ga ago. The supercontinent Kenorland was formed c. 2.72 Ga ago and then broke sometime after 2.45–2.1 Ga into the proto-continent cratons called Laurentia, Baltica, Australia, and Kalahari. The supercontinent Columbia or Nuna formed 2.06–1.82 billion years ago and broke up about 1.5–1.35 billion years ago.[14][15][not in citation given] The supercontinent Rodinia
Rodinia
is thought to have formed about 1.13–1.071 billion years ago, to have embodied most or all of Earth's continents and to have broken up into eight continents around 750–600 million years ago. See also[edit]

Phanerozoic

Paleozoic Mesozoic Cenozoic

References[edit]

^ a b James Monroe and Reed Wicander, The Changing Earth, 2nd ed, (Belmont: Wadsworth Publishing Company, 1997), p. 492. ^ "Pamela J.W. Gore, "The Precambrian". Retrieved on 10/05/11".  ^ "The Precambrian
Precambrian
Era". MIchigan State University.  ^ "Zircons are Forever". Retrieved 2007-04-28.  ^ International Commission on Stratigraphy. "International Chronostratigraphic Chart." Stratigraphy.org. Feb. 2017 (version 2017/02). <http://www.stratigraphy.org/index.php/ics-chart-timescale>. ^ Brun, Yves and Lawrence J. Shimkets, Prokaryotic development, ASM Press, Jan. 2000, p. 114 ISBN 978-1-55581-158-7 ^ Fedonkin, Mikhail A.; James G. Gehling; Kathleen Grey; Guy M. Narbonne; Patricia Vickers-Rich (2008). The Rise of Animals: Evolution and Diversification of the Kingdom Animalia. JHU Press. ISBN 9780801886799.  ^ Dawkins, Richard; Yan Wong (2005). The Ancestor's Tale: A Pilgrimage to the Dawn of Evolution. Houghton Mifflin Harcourt. ISBN 9780618619160.  ^ Terrestrialization (Precambrian–Devonian) ^ Clemmey, Harry; Badham, Nick (1982). " Oxygen
Oxygen
in the Precambrian Atmosphere". Geology. 10 (3): 141–146. Bibcode:1982Geo....10..141C. doi:10.1130/0091-7613(1982)10<141:OITPAA>2.0.CO;2.  ^ Geological Society of America's "2009 GSA Geologic Time Scale." ^ "Archived copy". Archived from the original on 2012-05-10. Retrieved 2011-03-27.  ^ Bleeker, W. (2004) [2004]. "Toward a "natural" Precambrian
Precambrian
time scale". In Felix M. Gradstein; James G. Ogg; Alan G. Smith. A Geologic Time Scale 2004. Cambridge University Press. ISBN 0-521-78673-8.  also available at Stratigraphy.org: Precambrian
Precambrian
subcommission ^ Zhao, Guochun; Cawood, Peter A.; Wilde, Simon A.; Sun, M. (2002). "Review of global 2.1–1.8 Ga orogens: implications for a pre-Rodinia super-continent". Earth-Science Reviews. 59: 125–162. Bibcode:2002ESRv...59..125Z. doi:10.1016/S0012-8252(02)00073-9.  ^ Zhao, Guochun; Sun, M.; Wilde, Simon A.; Li, S.Z. (2004). "A Paleo- Mesoproterozoic super-continent: assembly, growth and breakup". Earth-Science Reviews. 67: 91–123. Bibcode:2004ESRv...67...91Z. doi:10.1016/j.earscirev.2004.02.003. 

Further reading[edit]

Valley, John W., William H. Peck, Elizabeth M. King (1999) Zircons Are Forever, The Outcrop for 1999, University of Wisconsin-Madison Wgeology.wisc.edu – Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago Accessed Jan. 10, 2006 Wilde, S. A.; Valley, J. W.; Peck, W. H.; Graham, C. M. (2001). "Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago". Nature. 409 (6817): 175–178. doi:10.1038/35051550. PMID 11196637.  Wyche, S.; Nelson, D. R.; Riganti, A. (2004). "4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton". Australian Journal of Earth Sciences. 51 (1): 31–45. Bibcode:2004AuJES..51...31W. doi:10.1046/j.1400-0952.2003.01042.x. 

Wikimedia Commons has media related to Precambrian.

External links[edit]

Late Precambrian
Precambrian
Supercontinent
Supercontinent
and Ice House World from the Paleomap Project

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Geologic history of Earth

Cenozoic
Cenozoic
era¹ (present–66.0 Mya)

Quaternary
Quaternary
(present–2.588 Mya)

Holocene
Holocene
(present–11.784 kya) Pleistocene
Pleistocene
(11.784 kya–2.588 Mya)

Neogene
Neogene
(2.588–23.03 Mya)

Pliocene
Pliocene
(2.588–5.333 Mya) Miocene
Miocene
(5.333–23.03 Mya)

Paleogene (23.03–66.0 Mya)

Oligocene
Oligocene
(23.03–33.9 Mya) Eocene
Eocene
(33.9–56.0 Mya) Paleocene
Paleocene
(56.0–66.0 Mya)

Mesozoic
Mesozoic
era¹ (66.0–251.902 Mya)

Cretaceous
Cretaceous
(66.0–145.0 Mya)

Late (66.0–100.5 Mya) Early (100.5–145.0 Mya)

Jurassic
Jurassic
(145.0–201.3 Mya)

Late (145.0–163.5 Mya) Middle (163.5–174.1 Mya) Early (174.1–201.3 Mya)

Triassic
Triassic
(201.3–251.902 Mya)

Late (201.3–237 Mya) Middle (237–247.2 Mya) Early (247.2–251.902 Mya)

Paleozoic
Paleozoic
era¹ (251.902–541.0 Mya)

Permian
Permian
(251.902–298.9 Mya)

Lopingian
Lopingian
(251.902–259.8 Mya) Guadalupian
Guadalupian
(259.8–272.3 Mya) Cisuralian
Cisuralian
(272.3–298.9 Mya)

Carboniferous
Carboniferous
(298.9–358.9 Mya)

Pennsylvanian (298.9–323.2 Mya) Mississippian (323.2–358.9 Mya)

Devonian
Devonian
(358.9–419.2 Mya)

Late (358.9–382.7 Mya) Middle (382.7–393.3 Mya) Early (393.3–419.2 Mya)

Silurian
Silurian
(419.2–443.8 Mya)

Pridoli (419.2–423.0 Mya) Ludlow (423.0–427.4 Mya) Wenlock (427.4–433.4 Mya) Llandovery (433.4–443.8 Mya)

Ordovician
Ordovician
(443.8–485.4 Mya)

Late (443.8–458.4 Mya) Middle (458.4–470.0 Mya) Early (470.0–485.4 Mya)

Cambrian
Cambrian
(485.4–541.0 Mya)

Furongian (485.4–497 Mya) Series 3 (497–509 Mya) Series 2 (509–521 Mya) Terreneuvian
Terreneuvian
(521–541.0 Mya)

Proterozoic
Proterozoic
eon² (541.0 Mya–2.5 Gya)

Neoproterozoic era (541.0 Mya–1 Gya)

Ediacaran
Ediacaran
(541.0-~635 Mya) Cryogenian (~635-~720 Mya) Tonian (~720 Mya-1 Gya)

Mesoproterozoic era (1–1.6 Gya)

Stenian (1-1.2 Gya) Ectasian (1.2-1.4 Gya) Calymmian (1.4-1.6 Gya)

Paleoproterozoic era (1.6–2.5 Gya)

Statherian (1.6-1.8 Gya) Orosirian
Orosirian
(1.8-2.05 Gya) Rhyacian (2.05-2.3 Gya) Siderian
Siderian
(2.3-2.5 Gya)

Archean
Archean
eon² (2.5–4 Gya)

Eras

Neoarchean (2.5–2.8 Gya) Mesoarchean (2.8–3.2 Gya) Paleoarchean
Paleoarchean
(3.2–3.6 Gya) Eoarchean
Eoarchean
(3.6–4 Gya)

Hadean
Hadean
eon² (4–4.6 Gya)

 

 

kya = thousands years ago. Mya = millions years ago. Gya = billions years ago.¹ = Phanerozoic
Phanerozoic
eon. ² = Precambrian
Precambrian
supereon. Source: (2017/02). International Commission on Stratigraphy. Retrieved 13 July 2015. Divisions of Geologic Time—Major Chronostratigraphic and Geochronologic Units USGS Retrieved 10 March 2013.

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