Figures
- The role of extinction in evolution

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FiG. 1. Life spans of about 17,500 extinct genera of marine animals (vertebrate, invertebrate, and microfossil) tabulated from data compiled by Sepkoski (8).

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FIG. 2. Variation in intensity of extinction for 1-Myr intervals during the past 600 Myr, based on the species kill curve (9). "P1." refers to extinction intensity of the Pleistocene glacial epoch. Mass extinctions occupy the right-hand tail of the distribution. The mean extinction rate, 25% extinction per 1 Myr, is the approximate reciprocal of the mean species duration (4 Myr).

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FiG. 3. Kill curve (heavy line) for the past 600 Myr (9). Waiting time is the average interval between events of a given extinction intensity. Thus, for example, a short episode ofextinction which kills 30% of standing species diversity occurs on average every 10 Myr ("10-million-year event"), with no implication ofuniform periodicity in the spacing of events. Light curves bound the uncertainty in placement of the kill curve from fossil data (12).