Precambrian (or Pre-Cambrian, sometimes abbreviated pЄ, or
Cryptozoic) is the earliest part of Earth's history, set before the
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.
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
about 541 million years ago (Ma), when hard-shelled creatures first
appeared in abundance.
2 Life forms
3 Planetary environment and the oxygen catastrophe
6 See also
8 Further reading
9 External links
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
record is poorer than that of the succeeding Phanerozoic, and fossils
Precambrian (e.g. stromatolites) are of limited
biostratigraphic use. 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
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 (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.
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 (~4.6—4 billion), Archean
(4—2.5 billion), and
Proterozoic (2.5 billion—541 million) eons.
(There is only one other eon: the Phanerozoic, 541
million-present.) "Precambrian" is still used by geologists and
paleontologists for general discussions not requiring the more
specific eon names.
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 eon) from islands off
Greenland may be of organic origin. Well-preserved microscopic
fossils of bacteria older than 3.46 billion 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 (
Proterozoic eon) of the
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 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
Vendian biota. Hard-shelled creatures appeared toward the end of that
time span, marking the beginning of the
Phanerozoic eon. By the middle
of the following
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 is called the
Cambrian explosion of life.
While land seems to have been devoid of plants and animals,
cyanobacteria and other microbes formed prokaryotic mats that covered
Planetary environment and the oxygen catastrophe
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
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
Huronian epoch, roughly 2400–2100 Ma. One of the best studied is
Sturtian-Varangian glaciation, around 850–635 Ma, which may have
brought glacial conditions all the way to the equator, resulting in a
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.
At present, it is still believed that molecular oxygen was not a
significant fraction of
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.
Main article: Timetable of the Precambrian
view • discuss • edit
Earliest Earth (−4540)
Earliest sexual reproduction
Axis scale: million years
Orange labels: ice ages.
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. The
Precambrian Supereon is
divided into three eons: the
Hadean (4600–4000 Ma), Archean
(4000-2500 Ma) and
Proterozoic (2500-541 Ma). See Timetable of the
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 boundary. The
Proterozoic eon is divided into three eras: the
Mesoproterozoic and Paleoproterozoic.
Neoproterozoic: The youngest geologic era of the
Proterozoic Eon, from
Cambrian Period lower boundary (541 Ma) back to 1000 Ma. The
Neoproterozoic corresponds to
Precambrian Z rocks of older North
Ediacaran: The youngest geologic period within the
The "2012 Geologic Time Scale" dates it from 541 to 635 Ma. In this
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 Eon, 1000-1600 Ma.
Corresponds to "
Precambrian Y" rocks of older North American geology.
Paleoproterozoic: oldest era of the
Proterozoic Eon, 1600-2500 Ma.
Corresponds to "
Precambrian X" rocks of older North American geology.
Archean Eon: 2500-4000 Ma.
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
Hadean Eon. Other records from
Hadean time come from the moon
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
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
Cool Early Earth period) to the end of the Late Heavy
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
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 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.[not in citation given] The supercontinent
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.
^ 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".
Precambrian Era". MIchigan State University.
^ "Zircons are Forever". Retrieved 2007-04-28.
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^ Brun, Yves and Lawrence J. Shimkets, Prokaryotic development, ASM
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^ 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.
^ Dawkins, Richard; Yan Wong (2005). The Ancestor's Tale: A Pilgrimage
to the Dawn of Evolution. Houghton Mifflin Harcourt.
^ Terrestrialization (Precambrian–Devonian)
^ Clemmey, Harry; Badham, Nick (1982). "
Oxygen in the Precambrian
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^ Zhao, Guochun; Cawood, Peter A.; Wilde, Simon A.; Sun, M. (2002).
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^ Zhao, Guochun; Sun, M.; Wilde, Simon A.; Li, S.Z. (2004). "A
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Valley, John W., William H. Peck, Elizabeth M. King (1999) Zircons Are
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Wikimedia Commons has media related to Precambrian.
Supercontinent and Ice House World from the Paleomap
Geologic history of Earth
Quaternary (present–2.588 Mya)
Holocene (present–11.784 kya)
Pleistocene (11.784 kya–2.588 Mya)
Neogene (2.588–23.03 Mya)
Pliocene (2.588–5.333 Mya)
Miocene (5.333–23.03 Mya)
Paleogene (23.03–66.0 Mya)
Oligocene (23.03–33.9 Mya)
Eocene (33.9–56.0 Mya)
Paleocene (56.0–66.0 Mya)
Cretaceous (66.0–145.0 Mya)
Late (66.0–100.5 Mya)
Early (100.5–145.0 Mya)
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 (201.3–251.902 Mya)
Late (201.3–237 Mya)
Middle (237–247.2 Mya)
Early (247.2–251.902 Mya)
Permian (251.902–298.9 Mya)
Lopingian (251.902–259.8 Mya)
Guadalupian (259.8–272.3 Mya)
Cisuralian (272.3–298.9 Mya)
Carboniferous (298.9–358.9 Mya)
Pennsylvanian (298.9–323.2 Mya)
Mississippian (323.2–358.9 Mya)
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 (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 (443.8–485.4 Mya)
Late (443.8–458.4 Mya)
Middle (458.4–470.0 Mya)
Early (470.0–485.4 Mya)
Cambrian (485.4–541.0 Mya)
Furongian (485.4–497 Mya)
Series 3 (497–509 Mya)
Series 2 (509–521 Mya)
Terreneuvian (521–541.0 Mya)
(541.0 Mya–2.5 Gya)
Neoproterozoic era (541.0 Mya–1 Gya)
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 (1.8-2.05 Gya)
Rhyacian (2.05-2.3 Gya)
Siderian (2.3-2.5 Gya)
Archean eon² (2.5–4 Gya)
Neoarchean (2.5–2.8 Gya)
Mesoarchean (2.8–3.2 Gya)
Paleoarchean (3.2–3.6 Gya)
Eoarchean (3.6–4 Gya)
Hadean eon² (4–4.6 Gya)
kya = thousands years ago. Mya = millions years ago.
Gya = billions
years ago.¹ =
Phanerozoic eon. ² =
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.