An overview of the origin of life: The case for biological prospecting on Mars

Studies of the Earth's earliest biosphere have suggested a close coupling b etween the evolution of early life forms and the physical and chemical evol ution of the planetary surface. From a biological perspective there were ma ny similarities between early Earth and early Mars. This has led to the ide a that an origin of life event may have occurred on Mars, leading to the de velopment of microbial life. Various theories have been advanced to explain the origin of life on Earth, and these are reviewed with relevance to Mars . If traces of past or present biogenic activity are to be found on Mars, t hen the most likely place to prospect is several kilometers below the surfa ce where liquid water might be stable. Such prospecting may best lend itsel f to human exploration.