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neil

This is an interesting debate. Let's remember that there is no evidence for microbial life outside of the earth (discounting Gilbert Levin's interpretation of the Viking labeled release data). At present, what we have is conjecture. The argument seems to be "(1) we used to think life was restricted to particular environments on earth, (2) now we know it is found in niches once considered uninhabitable, (3) there may be similar niches elsewhere in the solar system, (4) therefore there may be life there too".

To my mind, active geological processes and biological processes are closely interrelated. On earth, we have "biogeochemical nutrient cycles" - the carbon cycle, the nitrogen cycle, the sulphur cycle. Over very long time periods, these cycles ultimately rely on a continual supply of elements that are cycled through the earths crust - swallowed by subduction zones and spat out through volcanic activity. So if microbes occupy niches on Mars, it would seem to me that we need a mechanism for biogeochemical nutrient cycling. In the absence of geological activity, it's harder to think up a suitable process.

I would love for methanogens to be discovered on Mars - I guess this one will play out for a long time yet. But I'm not sure about the idea that life can just "hang on" in small niches. James Lovelock's Gaia theory has influenced me a lot here - once life got a hold on Earth, it played a large part in shaping the planet, in terms of things like atmospheric composition. I suppose we can argue that evolution played out differently on Mars and what (hypothetical) life there was or is never managed to exert a global influence, but I think we need more precise theories and mechanisms and less conjecture.

Neil

Nathan Koren

So, if I may summarize the key points thus far for the layperson (ie, me):

1.) We've found a small but significant amount of methane on Mars. It's there for sure.

2.) This means either methane-respirating bacteria, or serpentinisation of olivine (or both).

3.) *Either* process requires the presence of liquid water environments on *present-day* Mars. This, alone, should be really big news.

4.) If it's life, well then that's the jackpot of course, but if it's serpentinisation, then that requires carbonates, which would also be awfully nice to find, given that we haven't seen any evidence of them thus far, and if Mars once had a thick CO2 atmosphere, then the carbonates *should* be there.

Have I got it right thus far?

Now some questions:

1.) If it's serpentinisation, is there a way to quantify, based on the CH4 output, roughly how much water and carbonates would be required? Are we talking about a handful of subsurface puddles, or a massive subsurface ocean?

2.) Okay, I'm going really far afield here -- my real-life discipline is architecture, so I really have no idea what I'm talking about -- but I seem to recall something to the effect that organisms on earth process various isotopes of 02 at different rates, and that measuring the ratio of these isotopes tells you something about the biological activity in any given atmospere. If I'm not making this all up, would it be possible to undertake a study of isotopic CH4 ratios on Mars, to determine whether the CH4 is biogenic or not?

Oh, and by the way -- thanks for the outstandingly superb coverage on this issue!!!

George

Fascinating stuff . . . Great blog.

Any thougths on the coating on the mars rock "Mazatzal" that Spirit's been looking at?
(ie the stuff that looks a lot like desert varnish)

Oliver Morton

Neil -- You're quite right about the interlinking of geochemical cycles and biology. And the Gaian point is crucial. If there is life on Mars then in one way Jim will be proved wrong -- life will have been found to be possible even when it doesn't play a key role in the planet's geochemistry. But the greater point might still hold; there could be a great difference between life playing a role and life not playing a role. Mars's Gaia could be dead, even while some remnants linger on. The components would persist, for a while, even after the system broke down.

Nathan -- I don't think you'd need that much serpentinisation for 300 tonnes a year -- certainly less than an ocean -- but I don't really know.
You're right that isotopes are the way to go: details are in the post "Where do we go from here".

George -- Haven't had a chance to think about Mazatzal (I seem to remember mentioning that it looked fun back in the days before methane took over the blog, but haven't followed up.)

Robert Clark

While volcanic eruptions on Mars may date to millions of years ago
there is evidence that volcanic venting is currently active on Mars:

*************************************************************************
From: Robert Clark (rgregoryclark@yahoo.com)
Subject: Active volcanic vent on Mars?
Newsgroups: sci.astro, alt.sci.planetary, sci.geo.geology
Date: 2004-02-12 12:58:08 PST

Take a look at a hires image on this page:

Portion of Valles Marineris.
http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=34528


Bob Clark
*************************************************************************
http://groups.google.com/groups?th=d6aa5ad5f46ec958

George

It's worth getting interested in Mazatzal, if the coating turns out to be desert varnish, and it's widespread, then that could be where the methane is coming from. Desert Varnish is not well understood, but is probably formed biologically.

At the moment, the coating is being touted as evidence of small amounts of water at Gusev, possibly underground:
http://www.spacedaily.com/news/mars-mers-04zzzo.html

Problem with the underground argument as I see it is that the rock is wind-eroded in the same way that the surrounding rocks are, (ie since it was ejected from bonnyville) so the coating has formed since the erosion took place. In view of the low erosion rates on mars, that could still be a long time ago, but equally it could be an on-going process.

I think it re-opens the debate about whether a very thin film of water bound to minerals would be stable or not at martian atmospheric pressure.

Tabaski

Sometimes on sundays don't have petlny to do and not after five in the morning , thus I'm sitting at the computer. Fancy sites powered by wordpress ,especially the design. Nice theme!

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