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Curiosity's Mars Crater Was Once a Vast Lake
astroengine writes The mountain that NASA's Mars rover Curiosity is exploring appears to have once been a lake, scientists said Monday. Mount Sharp, a three-mile-high mound of layered debris rising from the floor of Gale Crater, is believed to have formed billions of years ago, images posted on NASA's website ahead of conference call with reporters show. Sediments to create the mountain likely originated from the crater rim highlands and were transported toward the center of the crater in alluvial fans, deltas, and wind-blown drifts, scientists said. "During wet periods, water pooled in lakes where sediments settled out in the center of crater," NASA said. "Even during dry periods in the crater center, groundwater would have existed beneath the surface. Then, during the next wet period it would resurface to form the next lake. This alternation of lakes, rivers and deserts could have represented a long-lasting habitable environment."
It's not as if you're going to be able to crack open one of those rocks and find the Martian equivalent of a trilobite. For most of Earth's history, the dominant forms of life were microbes, and only in the last 600 million years or so when oxygen levels increase do large multicellular forms appear. Mars, assuming it ever had life, probably never got that far. So fossil evidence will consist of fossilized microbes- which will require cracking open rocks, thin-sectioning them, and inspecting them under a microscope. The other possibility is doing chemical analyses of the rocks and looking for geochemical evidence of life- isotopic ratios or organic compounds that could only be explained by the presence of life. Either way, it will require a fairly sophisticated laboratory. Either we have to conduct a sample-return mission, or we need to develop miniature laboratories that can be sent to Mars.
Although it now seems as if there is a third option. Recently, a meteorite was discovered which appears to represent a sedimentary rock from Mars. It's spendy stuff- $10,000 a gram- but that's vastly cheaper than a sample-return mission. A multimillion-dollar program to prospect for Martian meteorites on Earth is another way to look for Martian sedimentary rocks.