Asteroid impact fueled hail from hell

The asteroid that struck the Yucatan Peninsula 65 million years ago presumably initiated the extinction of the dinosaurs. The huge collision also unleashed a worldwide downpour of tiny BB-sized mineral droplets, called spherules.The hard rain did not pelt the dinosaurs to death. But the planet-covering residue left behind may tell us something about the direction of the incoming asteroid, as well as possible extinction scenarios, according to new research. The falling spherules might have heated the atmosphere enoughto start a global fire, as one example. How the spherules formed in the first place, though, has been a bit of a mystery.

One theory is that these half-millimeter-wide (0.02-inch-wide) globules precipitated out of a giant cloud of vaporized rock that circled the planet after the collision. "That vapor is very hot and expands outward from the point of impact, cooling and expanding as it goes," said Lawrence Grossman of the University of Chicago. "As it cools, the vapor condenses as little droplets and rains out over the whole Earth."Grossman and Denton Ebel, from the American Museum of Natural History, have shown that this vapor condensation model is consistentwith data taken from spherules around the world. The scientists also found that chemical differences in spherules from the Atlantic and Pacific Ocean imply that the vapor plume initially moved east, which might pinpoint the arrival direction of the asteroid.Apocalyptic fireball The spherules populate a 3-millimeter (0.12-inch) layer, called the K-T boundary, which separates the Cretaceous from the Paleogene (formally called the Tertiary) geologic periods. The abrupt disappearance of dinosaur fossils — as well as many marine fossils — above this boundary implies that a major extinction event occurred 65 million years ago.Around this same time, a city-sized asteroid landed near the present-day town ofChicxulub......