Figure: Distributary Fan: "Smoking Gun" Evidence for Persistent Water Flow and Sediment Deposition on Ancient Mars (Eberswalde Delta)

This MGS picture shows a long-lived delta with a complex and dynamic history: Countless scroll-bar flood events, 11 avulsions in top layer. It is clearly not due to one major bolide-induced catastrophic groundwater melt episode.

Such fluvial and delta deposits preserve the early sedimentary history of Mars and are therefore prime candidates for preserving fossil evidence of life.

It was probably raining on Mars during the Archean (3 billion years ago)!

Credit: Martian Deltas and the Origin of Life, by Janok P. Bhattacharya1, (Search and Discovery Article #40203, 2006) and NASA/JPL/Malin Space Science Systems.

http://www.searchanddiscovery.net/documents/2006/06058bhattacharya/index.htm