PBS Eons is a great youtube channel on Earth's biological history. It's very well done stuff. Their 'Purple Earth' video is a good layman's intro to some of the

PBS Eons is a great youtube channel on Earth's biological history. It's very well done stuff. Their 'Purple Earth' video is a good layman's intro to some of the per-oxygenation earth: https://www.youtube.com/watch?v=IIA-k_bBcL0 https://www.youtube.com/watch?v=IIA-k_bBcL0 The early biological history of Earth has a few 'Colored Earth' phases: Red-Purple-Green-White-Blue(hypothetically).