It's high time Earth got smacked with a comet. These firey globs of doom tend to come in cycles, raining down on our planet about once every 36 million years. Using a computer simulation of how our solar system moves through the Milky Way, astrobiologists at the UK's Cardiff University found that we pass through the densest part of the galaxy every 35 to 40 million years — they call it a "bounce." It turns out that comet impacts on Earth follow a similar cycle, increasing in frequency just about every 36 million years, give or take.
The data fits with the extinction of the dinosaurs 65 million years ago and another extinction at the end of the Paleocene period, 35 million years ago. It also means our planet's probably in for another life-ending black eye in the not too-distant future.
But what's Galactic density got to do with comet impacts? As the solar system moves through denser parts of the galaxy the extra gravitational pull upsets comets orbiting the Sun, sending them hurtling towards Earth. The theory's been tossed around for a while (and there are other good ones, like supervolcanoes, that haven't been discounted yet) but this new evidence makes it seems a little more believable.
It sucks to think that gravity — a pretty immutable force of nature — will be the source of our demise rather than something we can avoid, like global warming or nuclear war. But the study suggests there may be a silver lining to our extinction: comet impacts could be the driving force behind panspermia:
While the "bounce" effect may have been bad news for dinosaurs, it may also have helped life to spread. The scientists suggest the impact may have thrown debris containing micro-organisms out into space and across the universe.
Centre director Professor Chandra Wickramasinghe said: "This is a seminal paper which places the comet-life interaction on a firm basis, and shows a mechanism by which life can be dispersed on a galactic scale."
Image: The Alien Next Door