We've seen it countless times in the movies: An asteroid hurtling through space threatens life on Earth, and the heroes of the film are forced to come up with a way to stop its course and save the human race.
But what if the heroes didn't pull it off, and an asteroid actually smashed into the Earth? Would living organisms be able to survive an impact, or would the damage cause mass extinction?
Fortunately for anything with the usual biological processes, the chances of survival are a bit higher than you might think. Many experts believe the dinosaurs were wiped out by a deadly asteroid impact several millions of years ago, but many species survived the disaster, and we, of all animals, eventually made it to the top of the food chain.
Surviving a global catastrophe on the surface of the Earth is one thing, but are there any other options for struggling life forms following a devastating collision? In 2008, an international group of students from Germany, Russia, the United Kingdom and the United States published a research paper that tested the extraordinary possibility of bacteria surviving after impact with an asteroid. The study posed the interesting question of whether or not living organisms could either 1) be lifted outside of Earth's atmosphere on rocky debris and pulled back down to Earth or 2) be transferred, again via rocky debris, onto another potentially hospitable planet like Mars.
The students acknowledged the extreme difficulty of what's known as lithopanspermia, or the transfer of life from one planet to another by impact-expelled rocks. Any microorganisms attached to debris would not only have to survive the blast, they'd have to survive the ejection into space, the long journey (anywhere between 1 and 20 million years) from one planet to the next, radiation from the sun's rays and re-entry into the new planet's atmosphere.
They also point out that, in spite of the difficulty, the 40 Martian meteorites discovered on Earth suggest the trip has happened before. The students decided to test the particularly tough, radiation-resistant cyanobacteria called Chroococcidiopsis, usually found in hot deserts around the world. Using high explosives and high-pressure air guns to replicate the effect of an impact shock, they subjected the resistant bacteria, along with several others, to a lot of pressure. They arrived at the conclusion that survival is possible, but the bigger the blast, the better -- a large enough impact, somewhere between 5 and 50 GPa of pressure (diamonds form under about 10 GPa), would need to blow out the atmosphere to make escape less harmful for the organisms.
For lots more information on dazzling destructive bodies of energy floating through space, see the next page.