Has an Impact Done It Again?

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Science  21 Nov 2003:
Vol. 302, Issue 5649, pp. 1314-1316
DOI: 10.1126/science.302.5649.1314

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Researchers claim to have found more proof of a second major impact that triggered a mass extinction. But impact geologists say the newcomers still don't have the right kind of evidence to indict a second killer.