Free Astronomy Magazine March-April 2015

ASTROBIOLOGY tain the fossil evidence of their previous biological activity. The ideal environment in which MISS commonly form are the coastal areas of seas and lakes (where the water is suffi- ciently low to allow the photosynthesis process), but also regions subject to cycli- cal floods, such as those close to great riv- ers. That kind of bacterial colonies thrive until there is availability of water and energy, and in developing they accumu- late new vital layers (something similar to a coral reef) that overlap those of the pre- vious generations as far as reaching thick- nesses of a few centimetres. When water is definitely lacking, the growth of the mi- crobial mats ceases and the microorgan- isms die, leaving fossil traces in the MISS, also thanks to the fact of being integrated in sedimentary materials, which will in time petrify. Noffke has studied numerous cases of MISS that are still active, identifying 17 main groups and finding similar structures in increasingly older fossil sediments, go- ing far back as 3.48 billion years ago, in circled in red) is slightly higher and more intact, and can be con- sidered a part of the original bed of the lake that occupied the Gale Crater; Glen- elg, instead, is a more rugged and a little higher area. [NASA/JPL- Caltech/MSSS]