[X] My Assistant

[Bob Shaw]

One of the pre-MOLA hot topics was the supposed discovery of ancient Martiian shoreline features of various forms in, for example, Viking images. Now we have accurate height measurements, high quality MGS images, MOLA, and THEMIS data, and the whole subject has gone rather quiet, despite MEX images which are allegedly of glaciation and the remnants of ice floes.

I drove today from Glasgow to Gourock and back, and saw a 20 mile long raised beach; where are the Martian raised beaches?

Bob Shaw

[tty]

Those scottish raised beaches are Late Glacial or Early Holocene, i. e. about 10, 000 years old. Remember that any Martian ocean would only have existed quite early in Martian history while raised beaches and old shorelines are pretty short-lived features. I don't know of any older than the Pliocene here on Earth, but perhaps some of our geologist listmembers can think of older examples. Even on Mars I wouldn't expect to find any that are recognizable from orbit after 4 billion years, except in the very rare case where one was buried early on and just happened to be exhumed recently.
I think that in general we tend to underestimate how much Mars surface must have changed since the Noachian. Most of the surface we see has probably been cratered, buried and exhumed again and again since then.

Admittedly geologic processes work much faster here on Earth but it should be remembered how fast even large-scale geomorphic features erode away to nothing over geological time. Even major mountain-chains disappear in a few hundred million years. Admittedly there are places like Western Australia where Cretaceous river-valleys and Permian glacial topography are still recognizable, but this is very very unusual.

tty