You probably remember where you were when you heard the space shuttle Columbia had broken up on reentry in February of 2003.

Catherine Conley does. She's an astrobiologist with NASA's Ames Research Center, and had an experiment onboard Columbia that fateful day. Conley was studying the effects of microgravity on tiny worms called "nematodes."

When Columbia exploded, six canisters of these worms were blasted into the air and fell to Earth. The heat of the blast, the friction of the fall, the impact force of the crash, were all tremendous. Now comes the strange part. Conley was able to retrieve five canisters from the wreckage of Columbia, and all five still had live nematodes inside!

What does this tell us? No one had intended to do an experiment on whether it is possible for living organisms to survive a fall from space, but fate caused it to happen. The fact that the nematodes did survive inadvertently gives support to an idea known as "exogenesis."

Exogenesis is the hypothesis that life on Earth may have started somewhere else and then hitched a ride here on an asteroid. The idea is that a big chunk of rock collides with one planet, sending lots of small chunks into space, some of which eventually fall down on another planet. Those chunks might have life inside them, which then gets a start on its new world.

Some scientists had dismissed this notion as impossible because they thought nothing could survive being blasted off one planet and crashing down on another. However, Conley's unexpected discovery shows that exogenesis may not be so far-fetched after all.