Study Finds that a Single Impact Killed the Dinosaurs

["Richard W. Travsky" <rtravsky@uwyo.edu>]

http://www.redorbit.com/news/display/?id=747011

COLUMBIA, Mo.  The dinosaurs, along with the majority of all other animal 
species on Earth, went extinct approximately 65 million years ago. Some 
scientists have said that the impact of a large meteorite in the Yucatan 
Peninsula, in what is today Mexico, caused the mass extinction, while 
others argue that there must have been additional meteorite impacts or 
other stresses around the same time.

A new study provides compelling evidence that "one and only one impact" 
caused the mass extinction, according to a University of Missouri-Columbia 
researcher.

"The samples we found strongly support the single impact hypothesis," said 
Ken MacLeod, associate professor of geological sciences at MU and lead 
investigator of the study. "Our samples come from very complete, expanded 
sections without deposits related to large, direct effects of the impact 
for example, landslides  that can shuffle the record, so we can resolve 
the sequence of events well. What we see is a unique layer composed of 
impact-related material precisely at the level of the disappearance of 
many species of marine plankton that were contemporaries of the youngest 
dinosaurs. We do not find any sedimentological or geochemical evidence for 
additional impacts above or below this level, as proposed in multiple 
impact scenarios."
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