During the Proterozoic era, oxygen produced by photosynthesizing ... Iron present in exposed rocks reacts with this oxygen, and rust colors the planet red. While oxygen-loving organisms evolve ...

If Earth's history were a calendar year, humans would not appear until the last few minutes before midnight on Dec. 31. During the Proterozoic Eon—2.5 billion years to 543 million years ago ...

Earth surface processes in the Hadean and Archaean differ from those of the Proterozoic and, increasingly, the Phanerozoic. This occurs largely because of the impact of life on its environment, ...