From “Asteroid Craters On Earth Give Clues in Search for Life On Mars” (ScienceDaily, Apr. 17, 2012), we learn,
Craters made by asteroid impacts may be the best place to look for signs of life on other planets, a study suggests. Tiny organisms have been discovered thriving deep underneath a site in the US where an asteroid crashed some 35 million years ago.
Have we some reason for believing they weren’t here already, and managed to adjust to the impact?
Scientists believe that the organisms are evidence that such craters provide refuge for microbes, sheltering them from the effects of the changing seasons and events such as global warming or ice ages.
The study suggests that crater sites on Mars may also be hiding life, and that drilling beneath them could lead to evidence of similar life forms.
If we don’t know how life got started in the first place, we have no obvious reason to believe that Mars’ craters are hiding life.
That said, space agencies’ PR departments deserve full marks for not giving up in the face of massive budget cutbacks. If they ever do find life on Mars, it will be in spite of the level of support they are getting from government.
Volcanic glass theory here.