Free Astronomy Magazine March-April 2015

ASTROBIOLOGY T he three rock structures that make up the Yellowknife Bay formation: Sheepbed is the least high and most exfoliated part of the shal- low lakebed present in that area billions of years ago; Gilles- pie (roughly en- Among those scientists there was Nora Noffke, a highly distinguished and ex- perienced geobiologist, member of the Department of Ocean, Earth and Atmo- spheric Sciences of Old Dominion Univer- sity, Norfolk, Virginia. Nora Noffke has spent the last 20 years studying in various sites around the Earth a particular kind of natural conforma- tions, known by the acronym “MISS” (Mi- crobially induced sedimentary structures). These are structures that originate in shal- low water by the interaction between col- onies of microorganisms (from a few cen- timetres in size to several kilometres, ar- ranged over several layers, even a few centimetres thick and known as “micro- bial mats”) and sandstone deposits, on which the microorganisms (mainly cyano- bacteria and protozoa) act by modifying the normal sedimentary structure of the substrate on which they thrive. When these colonies of microorganisms become extinct due to changing environ- mental conditions, the sediments on which they lived can, under ideal conditions, re-