Word: asteroidal
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Dates: during 2000-2009
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...cloning, “Star Trek” to faster-than-light travel, and “2001: a Space Odyssey” to artificial intelligence and to the idea that human evolution might not be finished. Most lay-knowledge of science ranging from aliens and asteroid strikes to time-travel paradoxes and nuclear holocaust scenarios can all be traced back to the genre of science fiction...
...first has to do with the period's cataclysmic close. In lots of people's minds, the mystery of what killed the dinosaurs and other species - paving the way for the rise of mammals - was solved a couple of decades ago: a giant asteroid or comet slamming into the Earth, resulting in a dust cloud that shrouded the sun, cooled the planet dramatically and killed off plants and animals wholesale. It's a compelling story, but plenty of scientists never completely bought it. The dinos died pretty quickly, they admit, but not quite abruptly enough to be explained this...
...four billion years' worth of this sort of thing. Earth has had plenty of collisions too; it's just that erosion, continental drift and vegetation have erased or hidden most of them. Not all, though: Meteor Crater, in Arizona, was blasted out some 50,000 years ago by an asteroid about the same size as 2007 WD5. A much bigger object, a few miles across, is thought by many scientists to be the reason the dinosaurs died out some 65 million years...
...while it was still in orbit, so astronomers watched nearly two dozen individual impacts. But Jupiter is made mostly of thick clouds, so there was no lasting scar, and because it lies so far from Earth, the event wasn't quite as spectacular as this one promises to be. Asteroid 2007 WD5 should release some 3 megatons of energy if it slams into solid ground near Mars' equator, and orbiting satellites will show the aftermath with crystal clarity...
...calls to mind a loosely related incident that occurred almost exactly 100 years ago, when something exploded above the Tunguska region of Siberia, flattening trees in a 25-mile radius, their trunks pointing outward from the epicenter of the blast. Scientists are pretty sure it was a comet or asteroid - about the same size as 2007 WD5, as it happens - that disintegrated from its own shock wave as it plowed through the atmosphere. (UFO enthusiasts have long been convinced it was a flying saucer that somehow made it across trillions of miles of interstellar space safely, only to blow...