I just saw a talk by Paul Knauth that I call "How many planetary scientists can I piss off?" It was pretty funny. People were actually angry at him. And of course Knauth can be very patronizing when he wants to be.

His talk was about the claim of standing water on Mars. This deposit has cross beds, iron spherules, mineral casts, salts and jarosite. The Mars rover people interpres these as ripple marks, iron concretions, gypsum casts, and evaporites (respectively), leading them to conclude there was a lake on Mars. Knauth says all of these observations can be explained by a base surge deposit from and impact. Base surges can be cross beds and lapilli, which can be later oxidized to hematite. Because Mars has subsurface ice and brine, that is the source of the gypsum and salts. The jarosite formed later, like in iron mine tailings in Arizona.