Erosion rates on Mars and implications for climate change: Constraints from the Pathfinder landing site

The observation that the Mars Pathfinder landing site looks very similar to its appearance after it was deposited by catastrophic floods around 1.8-3. 5 Ga allows quantitative constraints to be placed on the rate of change of the site since that time. The abundance of erosional features such as an ex humed former soil horizon, sculpted wind tails, ripplelike and other lag de posits, and ventifacts (fluted and grooved rocks) all suggest the site has undergone net deflation or loss of 3-7 cm of material. The presence of barc han dunes and ventifacts argues for erosion by saltating crystalline sand-s ize particles entrained in the wind. Most ventifacts probably formed soon a fter the catastrophic flood, which likely introduced a large, fresh supply of sand-size particles distributed across the rocky plain. The strongest wi nds blew toward the northwest during this time, resulting in the sculpting of ventifacts, deflation of the surface, collections of dunes within Big Cr ater and other lows, and possibly preferentially eroding small crater rims. The predominant wind direction changed to blow toward the southwest, simil ar to today. These winds further deflated the surface, completed the deposi tion of sand-size material in dunes and ultimately trapped these dunes in l ows. The erosional features observed by Pathfinder indicate extremely low l ongterm deflation rates of 0.01-0.04 nm/yr since the end of the Hesperian ( 1.8-3.5 Ga) similar to less precise rates of <1 nm/yr based on the preserva tion of craters at the Viking 1 and Pathfinder landing sites. Short-term re distribution rates (deposition and removal) of atmospheric dust at the Path finder landing site and preexisting dust and sand at other locations on Mar s are up to 10(5) nm/yr, Estimates of erosion rates on Mars show a rapid de crease by 3-6 orders of magnitude from 10(2)-10(4) nm/yr in Noachian terrai ns (characterized by rimless, flat-floored craters and valley networks) to the exceedingly slow rates (10(-2)-10(-1) nm/yr) operating during the Hespe rian and Amazonian. Noachian erosion rates comparable to low continental de nudation rates on Earth are consistent with erosion by running water and pe rhaps a more clement climate. The rapid decrease in erosion rates is consis tent with a major climatic change during the Noachian, at the tail end of h eavy bombardment, and a cold, dry, desiccating climate similar to today's s ince that time.