Mars Life and Antarctica

This week, geologist Nora Noffke reports a study of Curiosity rover images that resemble Earth’s life forms. Noffke has long experience of interpreting fossils of ancient Earth in three billion-year-old rock formations such as Pilbara, Australia. In other words, writing grants persuading us to fund one’s camping in of Earth’s most scenic places.

The diagram above shows just one of her many images, with interpretation (the scale bar is 15 cm). It certainly looks like a modern microbial mat upon lake sediment, peeled back and rolled over in some places. Only organic life forms produce such flexible sheets of material, in layers associated with water (whose existence on Mars has also gained evidence). Surprisingly, perhaps, we have no statistical test to say, “that’s a microbial mat.” But the quality and quantity of the images may be our most compelling yet found.

Perhaps Noffke’s most convincing argument is that, were these rocks terrestrial, they would undoubtedly be accepted as fossils of ancient life. To be consistent: Either life existed on Mars three billion years ago–or it failed to exist on Earth.

Why is it so hard to find life on Mars? Microbial life can be incredibly subtle. I came to realize this during my explorations of Antarctica–arguably the best modern model for life without macrobiota.

The Antarctic Dry Valleys are a landscape in which all life is microscopic–that is, microbial or tiny invertebrates requiring magnification to see. There is no soil–because “soil” is a product of living bodies, plant detritus chopped by arthropods and processed by worms, feces of larger life. No soil, only sand and pebbles.

But here and there–where there is water–the microbes congregate in forms called mats or biofilms. Seeing these biofilms can be tricky.

In this example, I have outlined the bit of “stream mat” so you can see it. To find it, I noticed (after hours of hiking the sand) a sort of pasty trail, a few inches wide, descending from a glacier. The glacier had melted previously, sending a trickle of melt water down to the valley. Where the stream flowed, cyanobacteria had photosynthesized like crazy, growing a mat in the stream. Once the stream dried up, the mat dried too–you can see the pebbles trapped in it. This summer, if the mat gets lucky, the glacier will melt again, and  water will ooze once more down the mat. If not, the mat will dry and crack–and the wind might carry it to a nearby lake, where the edge melts in.

If the cyanobacteria end up in a lake, what grows there?

At the bottom of the lake, with barely a few photons to capture, the mats grow into amazing castles. (See Kay Vopel and Ian Hawes). Their cells make oxygen bubbles that ultimately lift bits of mat up to the ice, where the wind continually scrapes ice away, and eventually the mat bits surface–again to blow off to other lakes.

Who knows if such a mat cycle once happened on Mars? If it did, finding it would be quite a trick today.