This was originally posted on James Lewis’ personal blog at:
(Re-posted with permission)
Understanding if life could ever have existed on Mars is one of the most challenging scientific questions facing us in the 21st Century. We know that the Martian surface at present is an arid environment bombarded with ultraviolet radiation, so the chance of finding living organisms existing there today is extremely unlikely. However, Mars has not always been this way, its history is divided into three distinct geological periods; the Amazonian, Hesperian, and the Noachian. The oldest of these, the Noachian, is likely to have been a significantly more promising time for life to potentially evolve as liquid water persisted on or near the surface long enough to carve valleys into the Martian surface and leave behind distinctive rock units. For example, in Gale Crater Curiosity Rover discovered minerals that indicated the presence of a freshwater lake at the time of their formation billions of years ago, an environment favourable to life or at least life as we understand it on Earth.