The scientific dispute over what caused the extinction of 70 percent of all species worldwide 65 million years ago is closer to a resolution, with new research by scientists from UCLA and the University of Washington. The research was funded by the National Science Foundation (NSF).
A cover story in the November 22 issue of the journal Science reports the researchers' evidence supporting the controversial theory that the extinction of dinosaurs and many other species was caused by the impact of a huge meteorite that crashed to Earth some 65 million years ago.
"The end-Cretaceous extinction is one of the largest mass extinctions in Earth's history, and its cause has been among the most contentious, hotly debated issues in paleontology," says Chris Maples, program director in NSF's division of earth sciences. "This work by Marshall and Ward is important because it may result in more agreement among proponents of different end-Cretaceous extinction scenarios."
However, the scientists -- paleontologist Charles Marshall of UCLA and geologist Peter Ward of the University of Washington in Seattle -- also present evidence that other factors, including a drop in sea level prior to the assault by the massive asteroid or comet, also may have caused some of the extinctions at the end of what is known as the Cretaceous period. Marshall and Ward present evidence demonstrating that a combination of factors caused the mass extinctions.
Marshall applied statistical analysis to a well-preserved and well-documented fossil record which Ward has collected -- some 40 species of sea creatures from the Cretaceous period that include clams and squid-like creatures with shells called ammonites.
"For the first time, we can estimate the relative importance of
all the major factors that led to the extinction of the ammonites,"
says Marshall. The impact of the asteroid or comet accounts fo
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Contact: Cheryl Dybas
cdybas@nsf.gov
703-306-1070
National Science Foundation
21-Nov-1996