Hello Dan -

This work from Malin is fine, but you hit the problem right on the head - radiation.

It is amazing that Mars has a stratigraphy, but none the less not only does Mars have a stratigraphy but the process seems to be periodic. Since Mars does not have much of a tectonic process going on, the reasons for any stratigraphy have to lie in either periodic impact releasing a CO2
atmosphere, or in periodic solar variability.

Still, even given a periodic atmosphere, we don't see any life forms on the surface - I wish Clarke was right about some cactus, but...

It's the radiation. It sterlizes the surface -

Making the situation even worse, as concerns Mars use by man, the possiblity of sub-surface life forms increases -

EP
http://www.geocities.com/epgrondine