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The other thing, which I feel even more strongly about, is that many times, where there are microbial populations, they form these beautiful groups of filaments that just string out across the surface.
They almost look like the mane of a horse. Now the great thing is that, when minerals are deposited in these environments, they actually nucleate on these strings of filaments, and you get beautiful sedimentary textures that, again, look like the mane of a horse."
"You can see them in Yellowstone Park, in both siliceous and carbonate-precipitating strings. If you go to places like Mammoth Springs, you can see it happening today. And if you hike into the hinterland, you can see ancient examples of that, beautiful signatures preserved in the rock."In Rio Tinto, you can see iron depositing on these filaments; and in the 2 million year old terraces, you can see these filamentous iron textures. And there, again, I know of no process other than biology that could form those. So that's truly something to keep your eyes out for whenever you're looking at a precipitated rock on Mars