The 20-foot high cliff was window into the Superior Craton, one of the very first land masses to form when the planet was young. The original rocks likely included basalt from the ocean floor and volcanoes; granite from some of the first-ever continental crust; and mudstones formed as early Earth weather eroded rocks into smaller pieces and re-deposited them. Then, they were all buried deeply by more rocks being piled on top and the actions of plate tectonics, heated to 600-700 degrees Celsius, and metamorphosed. 

“This rock has experienced a LOT of Earth’s history,” said Tom, in a bit of an understatement.