The First Snowball Earth?

by Emil Morhardt

When did the first ice on Earth occur? About the only way to find out is to find old rocks with evidence of glaciation then determine exactly how old they are. A type of rock characteristic of glaciation is diamictite, a conglomerate-like mix of rocks with a large range of sizes held together with clay or mud that has been metamorphosed into mudstone. The large range of intermixed sizes in these deposits indicates lack of the size sorting that occurs in a river bed or floodplain, so some other source of disruption must have occurred, one of which is being scraped off and bulldozed along by a glacier. David Zakharov at the University of Oregon with a team of scientists from around the world (Zakharov et al., 2017) reasoned that if they could find examples of this type of rock that had formed near the equator, and could demonstrate that the water the rock encountered during formation came from glacial meltwater, then, they would have proven that at the time there were glaciers near the equator.  Continue reading