Hunting martian fossils best bet for locating Mars life, says ASU researcher
2007 AAAS Annual Meeting
February 16, 2007
San Francisco, CA

I agree, but it's not a very sensational conclusion. I've been looking for possible stromatolites from Sol 1, and I am sure I am not the only one.

Incidentally with HiRise it might just be possible to spot stromatolites. It does not seem likely, but it is certainly something to keep in mind.

For anyone interested this is what deeply eroded stromatolites look like:

http://ottawariverkeeper.ca/images/stromat...lain_bridge.jpg

And this shows a field of remarkably well-preserved ones (they look almost fresh as a matter of fact)

http://epod.usra.edu/archive/images/morocc...romatolites.jpg

At least you're not in that group of "interesting people" who claims to have found stromatolites on Mars

Farmer is suggesting that we should consider making more of an effort to look for evidence of past life on Mars. He suggests that evidence might be in the form of stromatolites. Terrestrial stromatolites are most often, although not always, preserved in limestone. With such a high percentage of carbon dioxide in the martian atmosphere, I don't think that calcite would be very easliy precipitated.

I wonder what type of deposit a Martian stromatolite would form.

In principle stromatolites can form in almost any material, as long as there is particulate matter that can be caught in a bacterial mat. Why not hematite or sulphates?

When I was in grad school at Wash U, St. Louis, we went on a field trip to the "St. Francis Mountains" in extreme southeast Missouri. It's billion year old ancient terrain that was buried by proterozoic and paleozoic rocks and is in the process of being exhumed. Some of the actual landscape is formed by the precambrian landscape that's being exhumed.

One of the sites, I think proterozoic, we stopped at was known for stromatolites and I collected some samples, some very nicely calcified with pink calcium carbonate, one was piece of wave-action brecciated pieces of the algae/bacterial mats all helter-skelter, then with the limestone dissolved out of the rock.

There were more pieces I collected, but they turned from stromato-lite's into stromato-heavy's on the trek back to the vehicles, and then into leaverites...Leave-'er-right-there.

The real challenge for any rover mission is to be able to spot microfossils and I don't mean just submillimeter size but microbial size. VERY non-trivial. Try to pack a machine that will make a thin-section of a rock on a rover. My brain hurts at the engineering implications of the thought.

Thin-slice? How about electron microscopy? Seems to me that they had to resort to such high magnifications to see what appear to be microfossils in that Martian meteorite. If all the little critters on Mars grew that small (not an unreasonable conjecture, given the harsh conditions and lower average energy levels in the environment), we'll need a rover that can prepare samples for, and subject them to, electron microscopy.

Sounds like a real challenge. Especially considering that there were plans (a long time ago) to provide Apollo astronauts *on the lunar surface* with equipment to make thin rock slices (part of the two-week lunar stay, dual-launch proposals for extended Apollo landings). So, I think that there are lots harder things to do, even remotely, than making and observing thin slices...

-the other Doug

Yeow. I can't see flying this kind of technology anytime soon, nor does the probability of successful detection seem significant enough to justify the cost. Furthermore, for all we know Spirit & Oppy have already photographed hundreds of "stromatolites" (biogenic rock structures) that just don't look even remotely like anything we've ever seen on Earth, so we can't identify them as such...different planet, different geochemistry=different frame of reference.

So, in my opinion, it's probably not worth doing a dedicated fossil hunting mission at this point because we don't really know what to look for. Now, if the crater wall gullies can be confirmed by MRO as actual subsurface aquifier outflows, then a dirigible able to drop down & grab samples from a recent flood deposit would be our best bet for finding current life.

Of course the Phoenix mission will have an atomic force microscope which "...will provide sample images down to 10 nanometers - the smallest scale ever examined on Mars."

No thin sections, but I'll bet plenty of people will be looking for martian diatoms, algae, and bacteria in those images.

A bacteria-sized organism would be enormous as seen by atomic force microscope.
Click to view attachment
http://library.thinkquest.org/10631/allabout/basics.htm


Here's an example of atomic force microscope observation of bacteria here on Earth.
http://www.mtholyoke.edu/~menunez/ResearchPage/AFM.html

And perhaps not. The important thing about stromatolites is that they are fairly independent of the organisms forming them. Essentially any organism forming sticky mats on the bottom of a waterbody can form stromatolites. In principle they could even form in other liquids than water.

Sure. Point is, it's very hard in my opinion to identify macrofossils (or the macro artifacts of microorganisms) on an alien world unless you have a detailed understanding of the primordial environment & its chemistry. For example, we see all sorts of symmetrical and/or odd-looking features in many of the MER pics, but certainly none so far that can't be much more simply explained by non-biological processes. Even the biogenic origin of many fossil stromatolites on Earth (esp. the oldest) is not completely certain.

All that being said, Phoenix's atomic-force microscope is very exciting...did not know about that, thanks! This instrument seems more than capable of identifying fossil cells; the trick is going to be distinguishing them from terrestrial contaminants.

EDIT: Here's a decent primer on AFMs: http://en.wikipedia.org/wiki/Atomic_force_microscope