Nick Hoffman wrote:
Just because erosion on Earth is normally on water does not mean Mars is the same. In fact the short time scales, extensive erosion, and lack of recharge (by either rain or groundwater) make water an unlikely material for this erosion.

Alex writes:
With all due respect Nick, this strikes me as a bit of circular reasoning, which is based on the presupposition that there was indeed a "lack of [hydrological] recharge" in the late Noachian. There is plenty of evidence (most notably relating to the ancient valley networks, as well as Malin and Edgett's sedimentary features) that show evidence for extensive water action at that time. Hynek and Phillips consider other types of erosion and conclude that precipitation-fed liquid water was the responsible agent.

Nick Hoffman wrote:
Sorry to sound the old scratchy record again, but you can often tell the quality of science as inverse to the hype of the press release.

Alex writes:
I agree, and moreover, I recommend that others read the actual paper itself, which is very well-written.

Alex R. Blackwell
University of Hawaii