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, 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 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 At ...
,
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 ...
,
hyoliths
Hyoliths are animals with small conical shells, known as fossils from the Palaeozoic era. They are at least considered as lophotrochozoan, and possibly being lophophorates, a group which includes the brachiopods, while others consider them as be ...
, and
mollusks.
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 the biogeochemical cycle by which carbon is exchanged among the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere of the Earth. Carbon is the main component of biological compounds as well as a major componen ...
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 formation ...
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.
However 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