Precambrian: Difference between revisions – Wikipedia
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The ”’Precambrian”’ (or ”’Pre-Cambrian”’, sometimes abbreviated ”’pꞒ”’, or ”’Cryptozoic”’) is the earliest part of [[History of the Earth|Earth’s history]], set before the current [[Phanerozoic]] Eon. The Precambrian is so named because it preceded the [[Cambrian]], the first [[geologic period|period]] of the Phanerozoic Eon, which is named after [[Cambria]], the Latinised name for [[Wales]], where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth’s geologic time.
The ”’Precambrian”’ (or ”’Pre-Cambrian”’, sometimes abbreviated ”’pꞒ”’, or ”’Cryptozoic”’) is the earliest part of [[History of the Earth|Earth’s history]], set before the current [[Phanerozoic]] Eon. The Precambrian is so named because it preceded the [[Cambrian]], the first [[geologic period|period]] of the Phanerozoic Eon, which is named after [[Cambria]], the Latinised name for [[Wales]], where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth’s geologic time.
The Precambrian is an informal unit of geologic time,{{cite book | title=The Geologic Timescale 2012 | volume=1 | publisher=Elsevier | editor=Gradstein, F.M. | editor2=Ogg, J.G. | editor3=Schmitz, M.D. | editor4=Ogg, G.M. | year=2012 | page=301 | isbn=978-0-44-459390-0}} subdivided into three [[eon (geology)|eons]] ([[Hadean]], [[Archean]], [[Proterozoic]]) of the [[geologic time scale]]. It spans from the formation of Earth about 4.6 billion years ago ([[Ga (unit)|Ga]]) to the beginning of the Cambrian Period, about {{Period end|Precambrian}} million years ago ([[Ma (unit)|Ma]]), when hard-shelled creatures first appeared in abundance.
The Precambrian is an informal unit of geologic time,{{cite book | title=The Geologic Timescale 2012 | volume=1 | publisher=Elsevier | editor=Gradstein, F.M. | editor2=Ogg, J.G. | editor3=Schmitz, M.D. | editor4=Ogg, G.M. | year=2012 | page=301 | isbn=978-0-44-459390-0}} subdivided into three [[eon (geology)|eons]] ([[Hadean]], [[Archean]], [[Proterozoic]]) of the [[geologic time scale]]. It spans from the formation of Earth about 4.6 billion years ago ([[Ga (unit)|Ga]]) to the beginning of the Cambrian Period, about {{Period end|Precambrian}} million years ago ([[Ma (unit)|Ma]]), when hard-shelled creatures first appeared in abundance.
History of Earth 4600–539 million years ago
The Precambrian ( pree-KAM-bree-ən, -KAYM-;[2] or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth’s history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth’s geologic time.
The Precambrian is an informal unit of geologic time,[3] 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 Period, about 538.8 million years ago (Ma), when hard-shelled creatures first appeared in abundance.
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 fossil record is poorer than that of the succeeding Phanerozoic, and fossils from the Precambrian (e.g. stromatolites) are of limited biostratigraphic use.[4] This is because many Precambrian rocks have been heavily metamorphosed, obscuring their origins, while others have been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.[4][5][6]
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 another planet called Theia shortly after it formed, splitting off material that formed the Moon (see Giant-impact hypothesis). A stable crust was apparently in place by 4,433 Ma, since zircon crystals from Western Australia have been dated at 4,404 ± 8 Ma.[7][8]
The term “Precambrian” is used by geologists and paleontologists for general discussions not requiring a more specific eon name. However, both the United States Geological Survey[9] and the International Commission on Stratigraphy regard the term as informal.[10] Because the span of time falling under the Precambrian consists of three eons (the Hadean, the Archean, and the Proterozoic), it is sometimes described as a supereon,[11][12] but this is also an informal term, not defined by the ICS in its chronostratigraphic guide.[13]
Eozoic (from eo- “earliest”) was a synonym for pre-Cambrian,[14][15] or more specifically
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