I never did write up those two talks I saw by Alan Howard back in the spring. Neither were great for water enthusiasts.

Relevent to this point was his talk on what Noachian landforms told us about erosion and climate then. Looking at the morphology of eroded Noachian craters, etc., he finds that on balance they tend to be supportive of fluvial rather than aeolian weathering. But, he noted that the total amount of erosion was equal to about 1 million to 5 million years in the U.S. Great Basin. (Note that that is during the period after large craters started being retained; doesn't include earliest Noachian periods which have been completely obliterated or buried planet-wide).

I.e., in the wettest period on Mars, in several hundred million years, total fluvial erosion comparable to a million or two years in Nevada. That is vastly more than the Moon or Mecury of course and so it's still pretty interesting as a different sort of planet, but it's not exactly moist and tropical either. I would imagine a million years worth of Nevada is also plenty to weather some igneous rocks into clay.

It actually reinforces a point made in Kim Stanley Robinson's Mars Trilogy. For all the unrealistic stuff, in the latter stages as all sorts of terraforming (and inadvertent modification due to wars, etc) are happening, lots of the landscape is virtually melting. Plenty of surface features are poorly consolidated, soluble (think Merdiani), or otherwise not very resistent to erosion. Give Mars just 1,000,000 years with a thick atmosphere, heavy rain, and an ocean, and I bet it'd look vastly different than it does today. There'd eventually be more of an equilibrium but what see today isn't it.

Another sci-fi anecdote. For an example of how incredibly dynamic Earth is, the "Map of Earth" on Ringworld is about 1,000,000 years old. Yet in "Ringworld Throne" (an execrable book), Mt. St. Helens in todays Washington State appears. Niven should have known better.

In fact, Mt. St. Helens is younger than the pyramids. Most of what got blown off in 1980 was newer than Nortre Dame. Mts. Hood, Ranier, and Shasta are all less than 1,000,000 years old. Conversly, there were other Cascade volcanoes then that are now just rugged, slightly elevated areas with a few rocky spires to mark the old conduits. On a regional scale it was similar, but would still be an utterly unfamiliar landscape to us.

Now imagine 3,800 such periods...