Throughout the history of Earth there have been numerous mass extinctions and there are just as many theories as to why they occurred.
The largest we know of occurred some 250 million years ago, give or take, but the mass extinction of the dinosaurs more recently has long been a favorite topic of scientists and philosophers.
Scientists at the Cardiff University Centre for Astrobiology have a new twist on an old idea and built a computer model to try and support it. Their model mapped our solar system’s movement and found that it continually “bounces” up and down through the plane of the galaxy. As we pass through the densest part of the plane, gravitational forces from the surrounding giant gas and dust clouds dislodge comets from their paths. The comets plunge into the solar system, some of them colliding with the earth.
They say we pass through this galactic plane every 35 to 40 million years, increasing the chances of a comet collision tenfold. Evidence from craters on Earth also suggests we suffer more collisions approximately 36 million years.
The periods of comet bombardment also coincide with mass extinctions, such as that of the dinosaurs 65 million years ago. Our present position in the galaxy suggests we are now very close to another such period.
Professor William Napier, of the Cardiff Centre for Astrobiology, said: “It’s a beautiful match between what we see on the ground and what is expected from the galactic record.”
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.”
The paper, by Professor Napier and Dr Janaki Wickramasinghe, is to be published in the Monthly Notices of the Royal Astronomical Society.