WASHINGTON (AP) Dinosaurs browsing in prehistoric America first saw death as a dark cloud approaching rapidly from the southeast. Within minutes, it hit: a wave of superheated, molten glass that scorched the Earth and helped end the 150-million-year reign of the dinosaur.
That's what Kenneth G. Miller and other experts at Rutgers University believe happened 65 million years ago when an asteroid 8 km in diameter slammed into what is now the Gulf of Mexico.
Miller said a 5-cm-thick layer of glass beads he and colleagues discovered in a deposit under New Jersey proves the asteroid impact sent a lethal wave of searing vapor ripping across the continent. The beads were found in drill cores brought up from 600-meter-deep boreholes beneath Bass River State Park, 21 km north of Atlantic City.
A report on the study was presented at the national meeting of the American Geophysical Union in Baltimore.
The glass, Miller said, came from rock and minerals that vaporized instantly when the asteroid hit just north of what is now the Yucatan Peninsula. The giant boulder from space smashed into the Earth at such a speed that the torrid vapor cloud would have spread across the continent at more than 20,800 kph.
The continent then was home to many types of dinosaurs, from Tyrannosaurus rex to 36-ton vegetarian sauropods. There was no escape for any of them, Miller said.
"The heated cloud would hate touched off forest fires and probably burned anything on the surface of North America," he said. The fires continued for weeks and weeks, filling the air with smoke and gas, blotting out the sun and chilling the air.
"Animals throughout North America would have been hard-pressed to survive, " Miller said . He said the glassbead deposit more than 2,400 km from the asteroid impact is "one of the final pieces in the puzzle of what happened to the dinosaurs."
Miller said his discovery is powerful evidence for the theory, first proposed in 1980 by geologist Walter Alvarez of the University of California, Berkeley, that a massive asteroid helped the dinosaurs to extinction.
He said Alvarez and his associates found worldwide chemical clues pointing toward an asteroid hit. Other scientists since have added more evidence, including discovery of the crater in the Gulf of Mexico.
Since New Jersey was covered by water 65 million years ago, said Miller, the 5-cm layer of glass spheres found there actually was deposited on the bottom of the ocean.
Miller estimated the cloud of vaporized rock took only 10 minutes to move from the asteroid impact site to where the researchers found the glass deposits. He said the superheated rock fell into the water and rained down onto the muddy ocean floor, where eventually it was covered by hundreds of meters of sediment.
Drill core samples from below and above the glass beads are consistent with specimens found elsewhere on Earth in geologic layers that mark the end of the Cretaceous period, the time of the dinosaur extinction, he said.
Below the glass beads, said Miller, there is fossil evidence of vigorous life. This was followed by a dead zone, which included the glass, and then more fossils as life reappeared.