The NY Times had this little article about the C. elegans worm:

The Indestructible Worm
When last we checked in on the tiny soil worm known as C. elegans, it had reached a pinnacle of scientific success. Not only was it the first animal to have its genome deciphered, but it had also become the favored laboratory specimen for studying how cells divide, differentiate and develop into organs, a role that contributed heavily to last year's Nobel Prize in medicine.

Now C. elegans has achieved another spectacular feat. Hundreds of the worms were on the space shuttle Columbia when it disintegrated. They survived the breakup, the fiery descent through the atmosphere and the jarring collision with the ground and kept on reproducing until they were found three months later.

Whether this was mostly luck, or because their canisters rode in a sheltered spot on the shuttle, or because of the worms' hardiness, is not clear. Their survival lends plausibility to the notion that life might have descended on Earth from other worlds in ancient times. If a tiny soil worm could do it, why not a hardy bacterium from a distant world, hitching a ride on a space rock or, dare we think it, sent by an advanced civilization?