BIOL 1001 Chapter Notes - Chapter 6.4: Invertebrate, Global Cooling, Paleobotany
28 Feb 2017
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Mass extinction is the rapid extinction of a large number of lineages scattered throughout the tree of life. When at least 60% of the species present are wiped out within 1 million years. The(cid:455)"re castrophic events that whiped out huge number of species & lineages in short time. Background extinction is lower, average rate of extinction observed when mass extinction is not occurring. (cid:862)big five(cid:863) (cid:373)ass e(cid:454)ti(cid:374)ctio(cid:374) eve(cid:374)ts. Mass extinction: results from extraordinary, sudden & temporary changes in environment. During mass extinction, species do not die out because individuals are poorly adapted to normal or gradually changing environmental conditions. Rather, species die out from exposure to exceptionally harsh, short-termed conditions- such as huge volcanic eruptions or catastrophic sea level changes. Background extinctions: thought to occur when normal environmental change, emerging diseases or competition with other species reduces certain populations to zero. Background extinctions are thought to result primarily from natural selection, mass extinction functions like genetic drift.
