Noachis Terra is an extensive southern landmass of the planet Mars. It lies roughly between the latitudes −20° and −80° and longitudes 30° west and 30° east. Environmental conditions favorable for the evolution of life on Mars may have occurred during the earliest period following planetary accretion, a time known as the Noachian (Noachis is the name given by classical astronomers to a region that we know today contains the oldest terrain on Mars). Geologic mapping identifies a variety of sites (such as valley outlets, topographic lows, depressions, and basins) in the martian tropical zone where water would have drained and perhaps been stable for hundreds of millions of years.