TABLE

Candidate Craters for the Impact-Kill Curve

Percentage of

Crater Size (km) species killed

Puchezh-Katunki 80 43

Chesapeake Bay 85 25

Manicouagan 100 62

Chicxulub 175 70

destroyed Hiroshima; according to Figure 24, it would result in the death of about 20 percent of species. A loss of 20 percent of species every 7 million years is equivalent to a 100 percent turnover in 35 million years, which is only about 6 percent of the time that has elapsed since the Cambrian began. Thus it is more than enough to account for the record of extinction observed in the rocks.

To answer Raup's question as he answered it: Yes, in theory, impact could have caused all extinctions. To turn the question around, since it is inescapable that the earth has been bombarded by meteorites of a range of sizes since life began over 3.5 billion years ago, and since even a modest-sized impact releases huge amounts of energy, how are we to escape the conclusion that not just in theory, but in practice, impact has caused many extinctions?

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