The Precambrian (Pre-Cambrian) is an informal name for the supereon comprising the eons of the geologic timescale that came before the current Phanerozoic eon. It spans from the formation of Earth around 4500 Ma (million years ago) to the evolution of abundant macroscopic hard-shelled animals, which marked the beginning of the Cambrian, the first period of the first era of the Phanerozoic eon, some 542 Ma. It is named after the Roman name for Cymru/Wales - Cambria - where rocks from this age were first studied. The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... In general usage, an eon (sometimes spelled aeon) is a very long period of time. ... The geologic time scale is used by geologists and other scientists to describe the timing and relationships between events that have occurred during the history of the Earth. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ... This article is about Earth as a planet. ... Annum is a Latin noun meaning year. ... For other uses, see Cambrian (disambiguation). ... In geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ... Look up eon, Eon, EON in Wiktionary, the free dictionary. ... For alternate meanings, see Wales (disambiguation) National motto: Cymru am byth (Welsh: Wales for ever) Official languages: English and Welsh Capital: Cardiff First Minister: Rhodri Morgan AM Area  - Total:  - % water: Ranked 3rd UK 20,779 km² xx% Population  - Total (2001):  - Density: Ranked 3rd UK 2,903,085 140/km² NUTS... This article is about the country. ... Cambria is a latinised form of Cymru, which is the Welsh name for Wales. ...

Overview

Remarkably little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what little is known has largely been discovered in the past four or five decades. The Precambrian fossil record is poor, and what fossils are present (such as those of stromatolites) are of limited use for biostratigraphic work.^[1] Many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.^[2][3] Geological time put in a diagram called a geological clock, showing the relative lengths of the eons of the Earths history. ... Pre-Cambrian stromatolites in the Siyeh Formation, Glacier National Park. ... This article or section does not cite any references or sources. ... Quartzite, a form of metamorphic rock, from the Museum of Geology at University of Tartu collection. ... During the Phanerozoic the biodiversity shows a steady but not monotonic increase from near zero to several thousands of genera. ...

It is thought that the Earth itself coalesced from material in orbit around the sun roughly 4500 Ma and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that came together to form the Moon (see Giant impact theory). A stable crust was apparently in place by 4400 Ma, since zircon crystals from Western Australia have been dated at 4404 Ma. To help compare orders of magnitude of different times this page lists times between 1017 seconds and 1018 seconds (3. ... Mars is the fourth planet from the Sun in the solar system, named after the Roman god of war (the counterpart of the Greek Ares), on account of its blood red color as viewed in the night sky. ... Planetesimals are solid objects thought to exist in protoplanetary disks and in debris disks. ... This article is about Earths moon. ... The Big Splash The giant impact theory (or Big Splash or Big Whack; cf. ... Zircon is a mineral belonging to the group of nesosilicates. ... Radiometric dating (often called radioactive dating) is a technique used to date materials, based on a comparison between the observed abundance of particular naturally occurring radioactive isotopes and their known decay rates. ...

The term Precambrian is somewhat dated, but is still in common use among geologists and paleontologists. It was briefly also called the Cryptozoic eon. It seems likely that it will eventually be replaced by the preferred terms Proterozoic, Archaean, and Hadean, and become a deprecated term. (See geologic time scale.) The Geologist by Carl Spitzweg A geologist is a contributor to the science of geology, studying the physical structure and processes of the Earth and planets of the solar system (see planetary geology). ... A paleontologist carefully chips rock from a column of dinosaur vertebrae. ... Look up eon, Eon, EON in Wiktionary, the free dictionary. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... The name Hadean refers to the geologic period before 3800 million years ago (mya). ... // For other uses, see time scale. ...

Life before the Cambrian

For more details on this topic, see Origin of life.

It is not known when life originated, but carbon in 3800 million year old rocks from islands off western Greenland may be of organic origin. Well-preserved bacteria older than 3460 million years have been found in Western Australia. 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 of the Precambrian. For the definition, see Life. ...

Excepting a few contested reports of much older forms from Texas and India, the first complex multicelled life forms seem to have appeared roughly 600 Ma. A quite diverse collection of soft-bodied forms is known from a variety of locations worldwide between 542 and 600 Ma. These are referred to as Ediacaran or Vendian biota. Hard-shelled creatures appeared toward the end of that timespan. Dickinsonia costata, an Ediacaran organism of unknown affinity, with a quilted appearance. ...

A very diverse collection of forms appeared around 544 Ma, starting in the latest Precambrian with a poorly understood small shelly fauna and ending in the very early Cambrian with a very diverse, and quite modern Burgess fauna, the rapid radiation of forms called the Cambrian explosion of life. The small shelly fauna is the name given to an obscure collection of small hard-shelled fossils found worldwide in beds a bit older than the earliest trilobites and archeocyathids in Nemakit-daldiyan stage (Lower Cambrian). ... Hallucigenia sparsa, one of the organisms unique to the Burgess Shale. ... The Cambrian explosion is the geologically kukko sudden appearance in the fossil record of the ancestors of familiar animals, starting about 542 million years ago (Mya). ...

Planetary environment and the oxygen catastrophe

Details of plate motions and such are only hazily known in the Precambrian. It is generally believed that small proto-continents existed prior to 3000 Ma, and that most of the Earth's landmasses collected into a single supercontinent around 1000 Ma. The supercontinent, known as Rodinia, broke up around 600 Ma. A number of glacial periods have been identified going as far back as the Huronian epoch, roughly 2200 Ma. The best studied is the Sturtian-Varangian glaciation, around 600 Ma, which may have brought glacial conditions all the way to the equator, resulting in a "Snowball Earth". The tectonic plates of the world were mapped in the second half of the 20th century. ... In geology, a supercontinent is a land mass comprising more than one continental core, or craton. ... In geology, Rodinia (from the Russian родина, or motherland) refers to one of the oldest known supercontinents, which contained most or all of Earths then-current landmass. ... A glaciation (a created composite term meaning Glacial Period, referring to the Period or Era of, as well as the process of High Glacial Activity), often called an ice age, is a geological phenomenon in which massive ice sheets form in the Arctic and Antarctic and advance toward the equator. ... The Huronian glaciation was from 2400 mya to 2100 mya, during the Siderian and Rhyacian periods of the Paleoproterozoic era. ... The Sturtian-Varangian is a late Precambrian world-wide glaciation episode ranging from 950Ma to 600Ma, represented by tillite deposits in Congo, Australia, China, North America, Sahara and Norway. ... One computer simulation of conditions during the Snowball Earth period. ...

The atmosphere of the early Earth is poorly known, but it is thought to have been smothered in reducing gases, containing very little free oxygen. The young planet had a reddish tint, and its seas were thought to be olive green. Many materials with insoluble oxides appear to have been present in the oceans for hundreds of millions of years after the Earth's formation. Air redirects here. ... ed|other uses|reduction}} Illustration of a redox reaction Redox (shorthand for reduction/oxidation reaction) describes all chemical reactions in which atoms have their oxidation number (oxidation state) changed. ... This article is about the chemical element and its most stable form, or dioxygen. ...

When evolving life forms developed photosynthesis, oxygen began to be produced in large quantities, causing an ecological crisis sometimes called the Oxygen Catastrophe. The oxygen was immediately tied up in chemical reactions, primarily with iron, until the supply of oxidizable surfaces ran out. After that the modern high-oxygen atmosphere developed. Older rocks contain massive banded iron formations that were apparently laid down as iron and oxygen first combined. Photosynthesis splits water to liberate O2 and fixes CO2 into sugar The leaf is the primary site of photosynthesis in plants. ... The Oxygen Catastrophe was a massive environmental change believed to have happened during the Siderian period at the beginning of the Paleoproterozoic era. ... 2. ...

Subdivisions

A diverse terminology has evolved covering the early years of the Earth's existence, but it is tending to settle out and come into greater use as radiometric dating allows plausible real dates to be assigned to specific formations and features. The terms Archean (older than about 2500 Ma), Proterozoic (2500-600 Ma), and Neoproterozoic (600-542 Ma) appear to have general currency. Some additional terms are included in the geological time line. See Timetable of the Precambrian. Radiometric dating (often called radioactive dating) is a technique used to date materials, based on a comparison between the observed abundance of particular naturally occurring radioactive isotopes and their known decay rates. ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... // This is a timeline of geological and relevant astronomical events on Earth before the Cambrian period started. ...

• Proterozoic : Modern use most often refers to the time from the lower Cambrian boundary, 542 Ma, back through 2500 Ma. The boundary has been placed at various times by various authors, but has now been settled at 542 Ma. As originally used, it was a synonym for "Precambrian" and hence included everything prior to the Cambrian boundary.
  • Neoproterozoic : the upper (i.e., youngest) geologic era of the Proterozoic eon, roughly from the Cambrian period lower boundary back to as far as 900 Ma, although modern use tends to represent a shorter interval : 542-600 Ma. The Neoproterozoic corresponds to Precambrian Z rocks of older North American geology.
    • Ediacaran : In March 2004, the International Union of Geological Sciences officially defined the term to describe this geologic period. The period begins at the time of deposition of a particular stratigraphic boundary, about 620 Ma. The period ends at the beginning of the Cambrian period, 542 Ma. In this period the Ediacaran fauna appeared.
    • Cryogenian a proposed subdivision of the Neoproterozoic.
    • Tonian a proposed subdivision of the Neoproterozoic.
  • Mesoproterozoic : the middle division of the Proterozoic. Roughly from 900-1600 Ma. Corresponds to "Precambrian Y" rocks of older North American geology.
  • Paleoproterozoic : The oldest subdivision of the Proterozoic. Roughly from 1600-2500 Ma. Corresponds to "Precambrian X" rocks of older North American geology.
• Archaean : Roughly from 2500-3800 Ma.
• Hadean : Prior to 3800 Ma. This term was intended originally to cover the time before any preserved rocks were deposited, although a very few old rock beds seem to be slightly older than 3800 Ma. Some zircon crystals from about 4400 Ma demonstrate the existence of crust in the Hadean Eon. Other records from Hadean time come from the moon and meteorites.

It has been proposed that the 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 could be divided into five "natural" eons, characterized as follows.^[4] The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... For other uses, see Cambrian (disambiguation). ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... The table and timeline of geologic periods presented here is in accordance with the dates and nomenclature proposed by the International Commission on Stratigraphy. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... For other uses, see Cambrian (disambiguation). ... The Ediacaran[5][6]  â€¢  â€¢  | Neoproterozoic (last æon of the Precambrian) Phanerozoic Axis scale: millions of years ago. ... IUGS logo The International Union of Geological Sciences (IUGS) is an international non-governmental organization devoted to international cooperation in the field of geology. ... In geology, a period or age is a time span of many millions of years that are assumed to have had similar characteristics. ... It has been suggested that the section Ediacaran biota from the article Ediacaran be merged into this article or section. ... The Cryogenian Period (from Greek cryos ice and genesis birth) is the second geologic period of the Neoproterozoic Era, followed by the Ediacaran Period. ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... The Tonian (from Greek tonas, stretch) is the first geologic period in the Neoproterozoic Era and lasted from 1000 Ma to 850 Ma (million years ago). ... The Neoproterozoic Era is the unit of geologic time from 1,000 to 542 +/- 0. ... The Mesoproterozoic era is a geologic period that occurred between 1600 and 900 million years ago. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Paleoproterozoic is the first of the three sub-divisions of the Proterozoic occurring between 2500 to 1600 million years ago. ... The Proterozoic (IPA: ) is a geological eon representing a period before the first abundant complex life on Earth. ... The Archean is a geologic eon; it is a somewhat antiquated term for the time span between 2500 million years before the present and 3800 million years before the present. ... The name Hadean refers to the geologic period before 3800 million years ago (mya). ... Zircon is a mineral belonging to the group of nesosilicates. ... Exploring Shorty crater during the Apollo 17 mission to the Moon. ... Willamette Meteorite A meteorite is a natural object originating in outer space that survives an impact with the Earths surface without being destroyed. ... A Global Boundary Stratotype Section and Point, abbreviated GSSP, is an internationally agreed upon stratigraphic section which serves as the reference section for a particular boundary on the geologic timescale. ...

1. Accretion and differentiation: a period of planetary formation until giant Moon-forming impact event.
2. Hadean: the Late Heavy Bombardment period.
3. 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.
4. Transition: a period of continued iron banded formation until the first continental red beds.
5. Proterozoic: a period of modern plate tectonics until the first animals.

The Big Splash redirects here. ... The Late Heavy Bombardment (LHB) was a period approximately 3. ... The Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland dated at 3. ... 2. ... Banded Iron Formations are a distinctive type of rock often found in old sedimentary rocks. ... The tectonic plates of the world were mapped in the second half of the 20th century. ... For other uses, see Animal (disambiguation). ...

References

1. ^ James Monroe and Reed Wicander, The Changing Earth, 2nd ed, (Belmont: Wadsworth Publishing Company, 1997), p. 492.
2. ^ Monroe and Wicander, p. 492.
3. ^ Pamela J.W. Gore, "The Precambrian". Retrieved on 12/6/06.
4. ^ Bleeker, W. [2004]. "Toward a "natural" Precambrian time scale", in Felix M. Gradstein, James G. Ogg, and Alan G. Smith: A Geologic Time Scale 2004. Cambridge University Press. ISBN 0-521-78673-8. 

• 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. and Graham C.M. (2001) Evidence from detrital zircons for the existence of continental crust and oceans on the Earth 4.4 Gyr ago. Nature, v. 409, pp. 175-178.
• Wyche, S., D. R. Nelson and A. Riganti (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 Volume 51 Zircon ages from W. Australia - Abstract Accessed Jan. 10, 2006

Image File history File links Commons-logo. ...

External links

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