New geological evidence in Italy suggests that impacts of
extraterrestrial objects, like asteroids or comets, could have been the cause of a mass extinction of life like the one in which the dinosaurs died out.
That extinction also is widely attributed to an impact.
Scientists reported in Friday`s issue of the journal Science the discovery of shattered quartz crystals embedded in shale dating back some 200 to 213 million years, at the end of the Triassic geological period. The shocked quartz, as they call it, is considered one of the most distinctive clues left by impacts of large meteorites or comets in the vicinity.
The scientists said the patterns of shocked quartz and their relation to other geological and fossil evidence in the Northern Apennines in Tuscany indicate that three closely spaced impacts seemed to occur at the end of the Triassic period. This was also the time of one of the five most devastating times of extinctions in Earth`s last half-billion years.
In their report the scientists, led by David Bice, a geologist at Carleton College in Northfield, Minn., concluded, ”The occurrence of what we interpret to be shocked quartz in several shale beds leads us to suggest that multiple impacts occurred in the latest Triassic, one of which coincided with a locally, and perhaps globally, significant extinction.”
Cathryn Newton, a paleontologist at Syracuse University and a co-author of the report, said in a telephone interview that this was the ”most tantalizing evidence” so far linking extraterrestrial impacts with another mass extinction.
Geologists generally believe that such impacts played a role in the widespread extinction of life, including the dinosaurs, at the end of the Cretaceous period 65 million years ago.
A relationship between impacts and extinction was hypothesized more than a decade ago by Walter Alvarez, a geologist at the University of California at Berkeley and a former teacher of Bice.
Although they concede that the impacts probably occurred, many paleontologists doubt that they were the main cause of the dinosaur extinctions. They contend that the impacts were only one of many complex forces driving disruptive global climatic change.
