A mass extinction is a geologically brief interval in which a large fraction of biological diversity disappears across many lineages. Its scale distinguishes it from ordinary losses of individual species, although the duration regarded as brief depends on the geological resolution.
The fossil record supplies evidence through disappearance patterns, but extinction selectivity, unequal preservation and sampling affect the observed signal. A regional disappearance is not sufficient evidence for global extinction; comparisons among regions and biological groups help test that inference.
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