By Daniel B. Wood, writer of The Christian Science Monitor
The Christian Science Monitor
RESEARCHERS at the University of Washington here say they have turned up new evidence that challenges the leading notions of how the dinosaurs became extinct.
The death of clams about 1 million to 2 million years before the large reptiles disappeared suggests major changes in ocean circulation and chemistry that point to a gradual, worldwide climatic change. For a decade or more scientists have been arguing whether or not sudden disasters - a meteor colliding with Earth, volcanic eruptions, or others - caused the extinctions. In those scenarios a thick cloud formed, blocking sunlight and cooling the planet.
But the new evidence suggests a change in sea-water chemistry, affecting both water and land plants and making the dinosaurs and thousands of other species ripe for a fall. In this case, volcanoes or a meteorite collision would have merely added to the trauma of species already compromised.
Reporting the new information at a recent meeting of the Geographical Society of America in Dallas, University of Washington geological sciences Prof. Peter Ward said: "If this oceanic event had not occurred, the dinosaur extinctions might not have either."
Beginning in 1980, Dr. Ward and graduate student Ken MacLeod collected scores of extinct clam fossils known as inoceramids from the stratified cliffs along the Bay of Biscay in Spain and France. …