Abstract: Large-Body Impacts are a Cause of Mass Extinctions

Eugene N. Shoemaker

Impacts on Earth of comets and asteroids form craters in the diameter range of 60 to 150 km at typical intervals of about 10 to 100 million years. These large impact events produce major short-term global perturbations of the climate. Known major impact events that are correlated in time with mass extinctions of biological species occurred near the end of the middle Miocene, in the late Eocene, at the Cretaceous-Tertiary boundary, at the Triassic-Jurassic boundary, and near the Frasnian-Fammenian boundary in the Late Devonian. Circumstantial evidence suggests that other mass extinctions may also be related to large body impacts.

The body which struck the Earth at the end of the Cretaceous produced a crater about 200 km or more in diameter on the northern tip of Yucatan. The ejecta from this crater formed a global fallout layer now recognized at more than 100 localities around the world in both marine and continental sediments. Extinction of marine planktonic species and angiosperm taxa occurred precisely at the time off or very shortly following, this major impact event, which may have been one of the largest in Phanerozoic time. The K-T impactor most probably was a comet.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994