I f 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 ...

The following Archean and Proterozoic eons produced the beginnings of life on Earth and its earliest evolution ... life on Earth dates at least from 3.5 billion years ago, during the Eoarchean Era, ...

The way amino acids are synthesized has changed during the history of ... age of bacteria and archaea. The Proterozoic eon was the gathering up of oxygen in Earth's atmosphere, and the Phanerozoic ...

Earliest animals evolved in the mid to late Proterozoic Eon and lie deep in the fossil record. Please give special attention to the photo credit, as it is from a participating researcher not from ...