History of Earth - in brief

History of Earth - in brief - Paleozoo. How old is the Earth? When did life first appear upon it? How did we come to be here? Questions as old as humankind. History of Earth - in brief - an outline of the evolution of the planet from its Hadean origins to its Anthropocene present. A timeline of the history of life on Earth. The Earth has undergone constant change in its billion year history, with life evolving in response to those changes - in particular to the changing atmospheric compositions of carbon dioxide and oxygen. Species extinctions have been a natural part of the evolutionary processes of the planet throughout its long history, however there are now thought to have been at least 8 mass extinction events in the history of the Earth - each of major consequence to life on the planet and of import to our modern understandings of climate change. There have been many extinction events, both great and small, but the most profound of these would be the End-Permian Extinc