Earth’s atmosphere is vital for diversity of life. Oxygen in the atmosphere developed early in earth history, before there were any complicated life forms.

How do we know this?            

The Copper Harbor Conglomerate is partly made up of alluvial fans. The alluvial fans are more obvious on the Keweenaw than on Isle Royale, where the sandy and silty units and more abundant and cobble sizes are generally less.  This alluvial fan hypothesis was proposed by Douglas Elmore in 1984. Many people have debated it and most support it. We make hypotheses like this to help us understand the conditions of formation of this remarkable rock formation.  There are some mind stretching implications: 1.  It implies a mountain on one side.  Where is that mountain now?  2. It suggests desert conditions. Without land plants, it is likely that the Neoproterozoic may have been a “wet” desert.