The Cambrian–Ordovician extinction event occurred approximately 488 million years ago (
mya). This early
Phanerozoic Eon
Eon or Eons may refer to: Time
* Aeon, an indefinite long period of time
* Eon (geology), a division of the geologic time scale
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* Eon, in the 2007 film '' Ben 10: Race Against Time''
* Eon, in the ...
extinction event eliminated many
brachiopods
Brachiopods (), phylum Brachiopoda, are a phylum of trochozoan animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear end, wh ...
and
conodonts, and severely reduced the number of
trilobite
Trilobites (; meaning "three lobes") are extinct marine arthropods that form the class Trilobita. Trilobites form one of the earliest-known groups of arthropods. The first appearance of trilobites in the fossil record defines the base of the ...
species. The Period in the Cambrian extinction in which most of the extinction occurred was the Caerfai Period.
It was preceded by the less-documented (but probably more extensive)
End-Botomian extinction event around 517 million years ago and the
Dresbachian extinction event about 502 million years ago.
The Cambrian–Ordovician event ended the
Cambrian Period
Period may refer to:
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* Full stop (or period), a punctuation mark
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* Period (music), a concept in musical composition
* Periodic sentence (or rhetorical period), a concept ...
, and led into the
Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya.
T ...
Period in the
Paleozoic
The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon.
The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838
by combining the Greek words ''palaiós'' (, "old") and ' ...
Era
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comp ...
.
Theories
*
Glaciation
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate be ...
*
Depletion of oxygen in marine waters
*
Flood basalt
A flood basalt (or plateau basalt) is the result of a giant volcanic eruption or series of eruptions that covers large stretches of land or the ocean floor with basalt lava. Many flood basalts have been attributed to the onset of a hotspot reac ...
event (
Kalkarindji
Kalkaringi (formerly Wave Hill Welfare Settlement, also spelt Kalkarindji ) is a town and locality in the Northern Territory of Australia, located on the Buntine Highway about south of the territory capital of Darwin and located about south ...
large igneous province
A large igneous province (LIP) is an extremely large accumulation of igneous rocks, including intrusive (sills, dikes) and extrusive (lava flows, tephra deposits), arising when magma travels through the crust towards the surface. The formation ...
, Australia)
Controversy
Soft-body fossils with morphology characteristic of the Cambrian have been uncovered in Morocco, dated 20 million years post-extinction. The 2010 paper by Roy, Orr, Botting, and their collaborators that announced the discovery suggests that Cambrian species persisted into the mid-Paleozoic. They argue that what had been interpreted as a Cambrian-Ordovician extinction is instead an artifact resulting from a gap in the stratigraphic record. Remains of soft-bodied animals prevalent in earlier, exceptional Cambrian fossil beds were only preserved in later, Ordovician deposits in rare places where special conditions promoted fossilization of soft bodies.
See also
*End-
Botomian
Cambrian Stage 4 is the still unnamed fourth stage of the Cambrian and the upper stage of Cambrian Series 2. It follows Cambrian Stage 3 and lies below the Wuliuan. The lower boundary has not been formally defined by the International Commission on ...
extinction event, circa 517 mya
*
Dresbachian
The Dresbachian is a Maentwrogian regional stage of North America, lasting from 501 to 497 million years ago. It is part of the Upper Cambrian and is defined by four trilobite zones. It overlaps with the International Commission on Stratigraphy, IC ...
extinction event, circa 502 mya
*
Geologic time scale
The geologic time scale, or geological time scale, (GTS) is a representation of time based on the rock record of Earth. It is a system of chronological dating that uses chronostratigraphy (the process of relating strata to time) and geochr ...
*
Furongian
The Furongian is the fourth and final epoch and series of the Cambrian. It lasted from to million years ago. It succeeds the Miaolingian series of the Cambrian and precedes the Lower Ordovician Tremadocian Stage. It is subdivided into three ...
, Late or Upper Cambrian period
*
Early Ordovician
The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. ...
period
Further reading
* Gradstein, Felix, James Ogg, and Alan Smith, eds., 2004. ''A Geologic Time Scale 2004'' (Cambridge University Press).
*
Hallam, Anthony
Anthony Hallam, aka Tony Hallam, (23 December 1933 – 23 October 2017) was a British geologist, palaeontologist and writer. His research interests concentrated on the Jurassic Period, with particular reference to stratigraphy, sea level c ...
and Paul B. Wignall, 1997. ''Mass extinctions and their aftermath'' (Oxford University Press).
* Webby, Barry D. and Mary L. Droser, eds., 2004. ''The Great Ordovician Biodiversification Event'' (Columbia University Press).
References
External links
Early Ordovician Climate
Extinction events
History of climate variability and change
Furongian extinctions
Early Ordovician extinctions
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