Stromatolite

Geologic age: 1.9 billion years ago, Proterozoic Eon

Region in Minnesota: Primarily northern Minnesota, but with some occurrences in southern Minnesota

Fast fact: These are the oldest fossils in Minnesota, and they were made by tiny photosynthesizing bacteria. They lived so long ago that there was not very much oxygen in the atmosphere. There were no predators on Earth, so these bacteria were able to become highly abundant and put out huge amounts of oxygen over the course of more than a billion years. That same oxygen has been cycling in and out of the atmosphere ever since. In fact, your ability to breathe today is all thanks to bacteria from billions of years ago, some from right here in Minnesota!