If Martian life existed a few billion years ago, scientists think any plant-like microbes would have left behind a stringy fuzz of fibers.
That's because here on Earth, researchers now say they have found such ancient fuzz, called cellulose, preserved in chunks of salt deposited more than 250 million years ago — making it the oldest biological substance yet recovered.
More: http://news.yahoo.com/s/space/20080331/sc_space/microscopicfuzzmaybebestevidenceofmartians