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Frontiers
The End of the World: More Proof of the Dinosaurs' Demise

October 1997

It was the most destructive day the world ever faced.

Sixty-five million years ago, a meteorite streaked into the atmosphere and hit Earth at Chicxulub, Mexico. The impact expelled a vapor cloud with devastating amounts of energy. Everything on Earth, from rocks and trees to dinosaurs and plankton, experienced the effects. They were either pulverized by the cloud's energy, or died later from the impact-induced tsunami and other secondary effects.

"The cloud was so fast-moving that it got from Mexico to New Jersey in about 10 minutes and fell to Earth. It formed a layer of glass beads, known as spherules, that is more than two inches thick," says Rutgers University geologist Kenneth Miller.

According to the researchers, the layer of spherules represents the most clear-cut evidence to date of the dinosaurs' demise. Miller, Richard Olsson and James Browning, all of Rutgers University; Daniel Habib, of Queens College in New York; and Peter Sugerman, of the New Jersey Geological Survey, presented their scenario at the spring meeting of the American Geophysical Union, as well as publishing it in the journal Geology. The geologists, jointly funded by NSF's Continental Dynamics Program in the Earth Sciences Division and by the Ocean Drilling Project (ODP) in the Ocean Sciences Division, were drilling the Bass River near Atlantic City, New Jersey, when they discovered the layer of glass.

The spherule layer occurs 1,260 feet below Earth's surface. Underneath it, the ground is chock-full of fossils, the remains of many plankton life forms that lived during the Cretaceous period. The sediment above the spherules layer, which was deposited in the Tertiary period, contains only a few fossils_90 percent of the planktonic life forms had been exterminated.

The spherule layer provides a tangible division between the two eras. Known as the Cretaceous-Tertiary boundary, it is the partition between the age of the dinosaurs and the age of mammals.

Until recently, the boundary was a mystery. Scientists knew that the dinosaurs and many of their contemporaries died, but no one was really sure how. However, with the discovery of this clearly defined spherules layer, as well as another spherule layer found by ODP scientists off the coast of Florida last February, researchers are feeling more certain about their description of the cataclysmic day.

Miller says the New Jersey spherule layer is "one of the final pieces in the puzzle of what caused the end of mass extinction at the end of the Cretaceous period." What's left to explore is what he refers to as the "kill mechanism."

While the vapor cloud and the meteorite killed anything in their path, the extermination of many species was global and rapid, so the secondary effects of the impact must have been equally devastating. Says Miller, "Many scientists favor a scenario in which dust from the impact shut down photosynthesis for a short period, resulting in the collapse of the food chain."


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