Rock Hounds 
You might think that you wouldn't have to be too careful about how you handle rocks that have been sitting in the desert for thousands of years. But scientists who are trying to determine whether a coating on the rocks was formed by living organisms take special care with them.
KUHLMAN: We try to approach from the downwind side because we're shedding DNA all the time.
Kim Kuhlman is a researcher who's studying rock varnish -- a coating found on some desert rocks -- and perhaps even on rocks on Mars.
KUHLMAN: We use sterilized gloves to pick up the rocks and brush off the dirt that's attached to them. And then we package them in sterile whirl-pack bags. Then we put them in canvas bags. Hopefully we don't puncture the bags, but inevitably most of the bags get punctured. So it's not a perfect process.
Rock varnish may be formed by bacteria. And Kulhman's studies have shown that even if it's not, bacteria can find a comfortable home below the varnish; more about that tomorrow. It's possible that rock varnish may have been seen on rocks on Mars. So figuring out how it forms has implications for life on the Red Planet.
Kuhlman and a student look for DNA in the varnish. But they have to filter out contamination. So in the lab, they use special clothing and filtered air to keep out their own DNA. They also use alcohol and bleach to clean their work areas and tools.
The precautions help ensure that any DNA they find is from bacteria in the rock -- and not from hitchhikers.
Script by Damond Benningfield, Copyright 2011