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   January 2000 


Life and death of the one hit wonders
The Chicxulub crater, made famous by the Cretaceous-Tertiary boundary impact that created it, may lose some of its distinction. Although the impact is unique in its extent of destruction—the mass extinction at the end of the Mesozoic—scientists assert that other asteroid and comet impact events may share similar environmental consequences.

“We have a good understanding of the Chicxulub event,” says David Kring, a professor in the Department of Planetary Sciences at the University of Arizona. Since 1991, when the significance of the impact struck the science community, Kring and his colleagues have calculated specific climatic effects such as carbon dioxide and sulfur emissions.

     A killer asteroid impact, such as the one illustrated above, may
     affect life similarly to smaller impacts. Dan Davis/NASA

By comparing the impact’s environmental effects to the paleontological record, scientists are beginning to assemble a good picture of how the Chicxulub impact affected life and have compared it to smaller impact events that may have fostered life within smaller regions.

At the October meeting of Geological Society of America in Denver, Kring summarized his own and other scientists’ research to illustrate how impact events have affected the environment and, by extension, life and its origin.

Impacts of asteroids as small as 0.3 kilometers in diameter can devastate life in a small region while creating hospitable habitats for other plants and animals to reclaim. Local and regional effects of impact events include fireball radiation, air blasts, earthquakes, tsunamis and burial of plants and animals by ejecta; but small impacts can also create crater lakes, springs and hydrothermal systems.

On average, the chance of these impacts occurring is once per 2,000 years (and because Earth is dominated by ocean, the chance of such an impact on land is once per 6,000 years, Kring says).

The Meteor Crater impact 50,000 years ago affected plants and animals within 40 kilometers, and probably destroyed those within a radius of 24 kilometers, Kring says. But it also created a lake when it penetrated the high water table. Cold-water fossils excavated from the crater suggest that the lake became an ecologically hospitable environment, thereby helping to rejuvenate life in an area demolished by the impact.

The heat the impacts produce can be sustained up to and exceeding 100,000 years because the heat is conducted into the rock surrounding the site. Over time, heat can drive hydrothermal systems to produce the type of high-temperature environments associated with life’s origin.

—Julia Cole
Geotimes contributing writer