Word: asteroidal
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Dates: during 2000-2009
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Astronomers have good news, better news and some bad news about an asteroid known as 2007 WD5. The good news is that this 164-ft.-wide chunk of speeding space rock, discovered in November in an ongoing search for potential threats to Earth, won't hit our planet any time in the foreseeable future. The better news - for eager space-watchers - is that the asteroid, currently about halfway between Earth and Mars, has a plausible chance of hitting the Red Planet at the end of January. If it does, astronomers will be treated to an unprecedented sight...
...extinction of the dinosaurs has long been considered a crime committed by a lone gunman: an incoming asteroid that struck the earth 65 million years ago, filling the air with sun-blocking dust. Now, however, controversy is being stirred anew as evidence suggests that the asteroid might have had a partner in crime: volcanoes, massive ones, blasting clouds of toxic gas from the bowels of the earth and poisoning much of the planet's life...
...that physicist Luis Alvarez and his son Walter, a geologist, proposed the giant-impact theory of dinosaur extinction. Their evidence was compelling: a thin layer of iridium in the earth's sediment dating to about the time of the die-off. Iridium is rare on Earth but common in asteroids. The iridium layer, mapped by the Alvarezes in scattered sites around the world, suggested an asteroid that vaporized on impact, spreading a cloud throughout the stratosphere. The argument seemed sealed in the 1990s, when geologists realized that a huge crater centered near Chicxulub, Mexico, was almost certainly caused...
...Keller's scenario, the Deccan eruptions began perhaps half a million years before the mass extinction. "This leads to greenhouse warming that puts a major stress on the environment," she says. Then came the asteroid impact, which pushed things further toward catastrophe. Finally, 300,000 years later, the eruptions reached their climax, sealing the dinosaurs' fate. "We've shown convincingly," she says, "the mass extinction came about 300,000 years after the asteroid impact...
Keller may be convinced, but others aren't. Sediment samples off the coasts of Senegal, Florida and Antarctica contradict her timeline, suggesting the mass extinction came right after the asteroid impact. "We've got beautiful sediments," says Brian Huber, a curator of paleontology at the Smithsonian Institution. "We have a continuous record of the event." Even 65 million years after the crime, the identity of the real perp is once again in dispute. And with eyewitnesses out of the question, the debate could go on for a while. India 65 million years ago and today...