The end-Botomian mass extinction event, also known as the late early Cambrian extinctions, refer to two extinction intervals that occurred during Stages 4 and 5 of the

Cambrian Period The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovici ...

, approximately 513 to 509 million years ago. Estimates for the decline in global diversity over these events range from 50% of marine genera up to 80%. Among the organisms affected by this event were the small shelly fossils, archaeocyathids (an extinct group of sponges),

trilobites Trilobites (; meaning "three-lobed entities") are extinct marine arthropods that form the class Trilobita. One of the earliest groups of arthropods to appear in the fossil record, trilobites were among the most successful of all early animals, ...

brachiopods Brachiopods (), phylum Brachiopoda, are a phylum of 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, while the fron ...

, hyoliths, and

mollusks Mollusca is a phylum of protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant species of molluscs are recognized, making it the second-largest animal phylum after Arthropoda. The num ...

Causes

There are several hypotheses for the causes of these extinctions. There is evidence that major changes in the

carbon cycle The carbon cycle is a part of the biogeochemical cycle where carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of Earth. Other major biogeochemical cycles include the nitrogen cycle and the water cycl ...

and sea level occurred during this time. Evidence also exists for the development of anoxia (a loss of oxygen) in some environments in the oceans. One hypothesis that unifies this evidence links these environmental changes to widespread volcanic eruptions caused by the emplacement of the Kalkarindji

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 format ...

or LIP. These widespread eruptions would have injected large amounts of greenhouse gases into the atmosphere causing warming of the climate and subsequent acidification and loss of oxygen in the oceans. Mercury anomalies have been discovered in strata corresponding to the extinction event; however, such enrichments in mercury are also found in older rocks that predate the biotic crisis. The precise timing between the eruptions and the extinction events remain unresolved.

References

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External links

Palaeos: Botomian

Cambrian Series 2 extinctions Extinction events