Apparent extinction intensity, i.e. the fraction ofgenera going extinct at any given time, as reconstructed from thefossil record. (Graph not meant to include recent epoch ofHolocene extinction event)
Theend-Botomian mass extinction event, also known as thelate early Cambrian extinctions, refer to two extinction intervals that occurred during Stages 4 and 5 of theCambrian Period, approximately 513 to 509 million years ago. Estimates for the decline in global diversity over these events range from 50% of marine genera[1] up to 80%.[2] Among the organisms affected by this event were thesmall shelly fossils,archaeocyathids (an extinct group of sponges),trilobites,brachiopods,hyoliths, andmollusks.[1][3][4][5]
There are several hypotheses for the causes of these extinctions. There is evidence that major changes in thecarbon cycle[6][7][8][9] and sea level occurred during this time.[1][10] Evidence also exists for the development ofanoxia (a loss of oxygen) in some environments in the oceans.[1][11][12]
One hypothesis that unifies this evidence links these environmental changes to widespread volcanic eruptions caused by the emplacement of theKalkarindjiLarge Igneous Province or LIP.[13][14][15] 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.[13] 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.[16] The precise timing between the eruptions and the extinction events remain unresolved.[14]
^Zhu, Mao-Yan; Zhang, Jun-Ming; Li, Guo-Xiang; Yang, Ai-Hua (2004). "Evolution of C isotopes in the Cambrian of China: implications for Cambrian subdivision and trilobite mass extinctions".Geobios.37 (2):287–301.doi:10.1016/j.geobios.2003.06.001.
^abEvins, Lena Z.; Jourdan, Fred; Phillips, David (2009). "The Cambrian Kalkarindji Large Igneous Province: Extent and characteristics based on new 40Ar/39Ar and geochemical data".Lithos.110 (1–4):294–304.doi:10.1016/j.lithos.2009.01.014.hdl:20.500.11937/35356.
^abGlass, Linda M; Phillips, David (2006). "The Kalkarindji continental flood basalt province: A new Cambrian large igneous province in Australia with possible links to faunal extinctions".Geology.34 (6): 461.doi:10.1130/G22122.1.ISSN0091-7613.
^Kravchinsky, Vadim A. (2012). "Paleozoic large igneous provinces of Northern Eurasia: Correlation with mass extinction events".Global and Planetary Change.86–87:31–36.doi:10.1016/j.gloplacha.2012.01.007.
