During the Proterozoic era, oxygen produced by photosynthesizing bacteria collects in the oceans and then in the atmosphere. Iron present in exposed rocks reacts with this oxygen, and rust colors ...

Sinkholes like the Middle Island one don't have oxygen. Neither did Earth 2.5 billion years ago at the start of the ...

Often overshadowed by the more data-rich Phanerozoic Eon, this period was characterized by critical evolutionary, environmental, and tectonic changes. However, the fossil record of Proterozoic ...

Proterozoic, and Phanerozoic eons. Each eon is subdivided into eras. The Phanerozoic Eon is divided into the three eras. The oldest is the Paleozoic Era, which means ‘ancient life’ and ...