Posted: Tue, Jan 28, 2003, 7:29 AM ET (1229 GMT)
Columbia University scientists believe that major asteroid and comet impacts on the Earth may trigger periods of intense volcanic activity. The study, published in this month's issue of the journal Earth and Planetary Science Letters, studied ten major peaks in impact events found in the geologic record. In nine of those cases scientists also found increases in mantle plume volcanism at the same time. Scientists aren't certain why impacts would increase volcanic activity, but they suggest that could crack the crust or even create new plate boundaries, making it easier for mantle plumes to reach the surface. The studies also raise the question of whether impacts themselves caused the mass extinctions associated with them, or if volcanism also contributed.

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•  Columbia University press release