The Snowy Range is composed of a sequence of formerly sedimentary (now metamorphic) rocks tilted almost vertically. The Nash Fork Formation includes the sugary white quartzite of the mountain peaks as well as layered metadolomites deposited in shallow water along a coastline formed soon after the appearance of oxygen in Earth’s atmosphere. Mats of photosynthetic microbes colonized rocks in this shallow water when our planet was half its current age. At that time there was no life whatsoever on land, and these colonies of microscopic organisms were the most complex life on Earth. These fossils are 20 times older than dinosaurs.
In August 2015, we joined a tour led by geology Professor Donald Boyd of the University of Wyoming, to learn about these fascinating fossils. some of the mounds made by these creatures are the size of my car! You can see the way they captured passing silt and concentrated it in layers. You can see how little filaments of microbial slime rose up through the silt, seeking the light of a Sun that had not yet reached its full illumination.
Over thousands of millions of years since, the cells themselves and the silt they collected have been replaced by silica (quartz), so the microbial layers stand out as sharp ridges above the carbonate surface beneath. Modern limestones and dolomites form almost entirely from tiny fragments of shells, but the paleoproterozoic carbonates in the Nash Fork formation were chemically precipitated because they formed more than a billion years before the evolution of life with hard parts!