Working with the exobiology division at NASA, which is primarily concerned with space science and the search for life in the solar system, Farmer realized that, if early evolution of life occurred on Mars, planned Mars exploration missions could present a unique opportunity to bag some evidence of fossilized Martian microbes. Water and carbon-based molecules are essential components to life as we know it here on Earth. Mars is the only planet in our solar system believed to have had liquid water on its surface for any part of its geologic history. The 1978 Viking missions detected evidence of ancient running water and of glaciers that once scoured the surface of Mars. But the Viking landers also confirmed that harsh surface conditions present on the planet today do not allow for liquid water or life-forming compounds to exist.
Water remains near the surface only as ice.
Mars' atmospheric pressure is less than a hundredth of that on Earth, which causes any liquid water to vaporize immediately. But fossil evidence of life that could have evolved when Mars still had a substantial atmosphere could be hidden in the surface rocks. If we run the clock backwards, it is likely that the atmosphere was denser on Mars, entrapping heat and warming the planet's surface above the freezing point. If Mars was warmer and wetter in its early days, it is conceivable that microorganisms evolved. Geothermal hot spots, such as those found in Yellowstone National Park, are home to ancient bacterial families and fossilized ancestors that could play a significant role in understanding the early evolution of life on Earth.