Meteorite find aids theory of catastrophe

Press, 23 August 1983, Page 6

Meteorite find aids theory of catastrophe

NZPA Rochester, New York A layer of clay found in Denmark and on the bottom of the Pacific Ocean supports a theory that a very large meteorite struck Earth 65 million years ago, about the time the dinosaurs became extinct, a researcher says.

The clay mineral smectite found in two drill-core samples seems to be a decayed form of glass dust such as might have been produced by a large meteorite impact, says Dr Miriam Kastner of Scripps Oceanographic Institute in La Jolla, California. The samples came from the Stevns Klint region of Denmark and deep-sea drilling project hole 465 a in the north-central Pacific.

Layers of smectite, a common decay product of glass, have previously been found in 36 places around the world, indicating the debris was evenly spread across the planet, Dr Kastner said.

“I think it’s very conclusive that there was a meteor impact,” she said.

Scientists could not be sure the meteorite caused the dinosaurs’ extinction, but, “that is a time we had major extinctions. Now the question is, did it cause the extinction or was it coincidental?”

She presented her findings recently at an international conference on glass at Alfred University in Alfred, New York. Drs Luis and Walter Alvarez of the University of California at Berkeley first theorised in 1980 that the dinosaurs died out at the

end of the Cretaceous period after a meteorite roughly 10km across struck and threw millions of tons of debris into the atmosphere, cooling the planet and burying or killing their food supply. Their theory was based partly on the finding of high levels of the metal iridium in the smectite layers. Iridium is 1000 times more prevalent in meteors than on the Earth’s surface. Dr Walter Alvarez and two colleagues at Lawrence Berkeley Laboratory, who are listed as co-authors on Dr Kastner’s paper, analysed the two samples and again found high concentrations of iridium, Dr Kastner said. The samples also had unusual amounts of platinum, gold, nickel and cobalt, also common in meteorites, she said. Dr Kastner said the smectite layer at the two sites was very pure, suggesting it was deposited in a single catastrophic event. Paleontologists trying to confirm the catastrophe theory of dinosaur extinction have found evidence in microscopic marine plant fossils of a sharp rise in temperature and then prolonged cooling within 10,000 years of the suspected impact, she said. A meteorite landing in the ocean might have thrown up water vapour, heating the atmosphere through a “greenhouse effect” by trapping heat, she said. When the water condensed and the debris remained in the upper air, the atmosphere would cool.