Mark asked:

>Why can't the Olivine come from volcanic eruptions post dating wet Mars?
>There is strong evidence Martian volcanism was active far past the supposed
>wet period.
>
>Why couldn't carbonates formed during a wet period be buried under the
>lavas discussed above? Being coated with ash then lava would not release
>the CO2 as it would during crustal recycling on Earth.

You presuppose there was a "wet Mars". Because the Sun is a main sequence star, we know the surface luminosity experienced by Mars has never been brighter than it is today. The only tenable theory for a "wet Mars" is one
based upon a green house effect. If Mars had a denser atmosphere then where is that atmosphere today? Where are the carbonates that would be the relic of that ancient atmosphere? There should be mountains of it like the Dolomite Mountains in Northern Italy. Only recently have tiny quantites of carbonates been detected.

>Why should CH4 produced subsurface be detectable after passing through
>highly oxidative top regolith?

There's detectable CH4 in the Earth's upper atmosphere. That CH4 is
coexisting with atomic oxygen. How is this possible? Answer: The CH4
is being regenerated faster than it is being decomposed. Are you
proposing that the martian soil is more oxidizing that the Earth's upper
atmosphere? If so, why do you believe that life could survive in such an
environment?

>Why should an always cold Mars preclude subsurface evolution of life in
>geothermally heated aquifers? Even Nick seems open to this idea.

I'm reluctant to disagree with Nick. However it is my understanding that
none of the martian volcanoes are active and Mars maybe geologically dead.
I believe(?) Nick is open to the concept of "deep dark life", e.g. hydrogen
metabolism micro organisms. The concept of deep dark life on Mars can not
be dismissed although the lack of detectable methane weighs against it. I'm
skeptical that biological genesis can occur on a world without oceans. The
theory that Mars once had oceans is no longer accepted. If Mars once had
oceans enabling biological genesis, then it would be credible that some
life forms could evolve to live deep underground. However I am skeptical
that life originated deep underground (I believe Nick might disagree with
me on this last point). To recap, my point of disagreement with Nick might
be the necessity of an ocean for biological genesis. Other readers should
note that I am only a humble engineer and Nick does geology for a living.

Gary