THE EARLY MARTIAN ATMOSPHERE

New research suggests that the early Martian atmosphere, 3.6 billion years ago, would have led to cold, dry conditions on the planet: Mars was not a permanently warm wet world.
http://www.bbc.co.uk/news/science-environment-27039711

The technique used was to calculate the early Martian atmospheric pressure from patterns of ancient meteor craters and dry river beds seen today on the Martian surface. If the atmosphere was thick, small meteors would burn up before reaching the surface; but some craters in the Aeolis Dorsa region near Gale Crater on Mars are small, only a few tens of metres across. suggesting quite small meteors survived through the thin atmosphere and impacted the surface.

Lead author Dr Edwin Kite said: ' Conditions were mostly very cold and very dry even on early Mars - similar to the Antarctic Dry Valleys on Earth today. However, there is still plenty of microbial life even in the Antarctic Dry Valleys so our work doesn't rule out an early environmental niche for life on Mars.'

It seems that surface water was not permanently present on early Mars, and that periods when the temperature got above freezing were rare or periodic.