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NASA will soon begin rolling Curiosity toward this area.

Here is a blow-up of some of the hills:

To my geologically untrained eye, these hills appear to have sedimentary layers.

(Continued below the orange Martian hills.)

On Earth, sedimentary layers would contain organic materials deposited by bacteria and other organisms that had been living in the water that made the layers. Those organic materials would have specific isotope ratios, resulting from metabolic reactions that preferentially select isotopes in ways abiotic chemistry cannot. This is because enzyme activity is sensitive to tiny differences in electronegativity resulting from different amounts of neutron charge shielding in the nuclei of different isotopes of an element.

Thus on Earth, biologically-deposited materials have isotope abundances that provide a signature of past metabolic activity. Those isotope ratios would provide quick evidence that life had been there when the layers were deposited.

But on Mars, even if there was life there in the past, we have no idea what its biochemistry might have been like. It is a reasonable guess that it too would have had biochemical pathways honed by natural selection, and that Martian life would require special catalysts that would probably also be able to create peculiar isotope ratios, just as Earth enzymes do.

So although nobody knows what isotope ratios would be a signature of past Martian life, there will be a lot of attention paid to whatever ratios Curiosity measures, and a lot of discussion about whether some abiotic process could have produced them, or whether they are evidence of biology.


As the months go by and we see more pictures, keep your eyes open for anything like this:

This is Banded Iron Formation rock, made by photosynthetic bacteria billions of years ago (on Earth!). The bacteria produced oxygen, precipitating out iron oxide from the oceans which at that time were full of unoxidized iron. Eventually all the iron in the oceans was oxidized, and the oxygen produced by the photosynthetic bacteria began to be released into the atmosphere.

Originally posted to atana on Sat Aug 18, 2012 at 03:29 PM PDT.

Also republished by Astro Kos.

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