Re: Does NASA conduct pre-explorations of Mars life signs on Earth?

Missed this in my inbox... Close, but not quite, to answer your question. 
NASA rover prototypes aren't tested in what we would call "extremophile"
environments (high temperature or acidic environments).  They're tested on
Earth, under Earth gravity, in similar soil environments.  NASA does have
soil laboratories which create artificial soils meant to match the soil
conditions on Mars and the Moon for its rovers, yes, and tests them in
those.  To my knowledge, though, they still test in Earth atmosphere under
normal temperatures and pressures.  Mars has about 1% of our atmosphere's
density and is made of carbon dioxide, so it's a bit different, but the
soil simulation is generally sufficient to provide (especially under our
higher gravitation) a very thorough test of rover operations.  After all,
it's usually the wheels and things in contact with the soil which give out
first.