The age of the Earth was determined by using absolute dating of meteorites and moon rocks, which gives a date of 4.5 billion years old. The oldest known Earth rocks are younger, at just more than 4 billion years in age. Older Earth rocks have been destroyed by meteorite impacts, weathering, or metamorphism.

The oldest known fossils are almost 3.8 billion years old. The oldest fossils, however, are from very simple, single-celled forms of life. They are far removed from the complex life forms of the present. Multi-celled organisms (our likely ancestors) did not appear until approximately 650 million years ago. These creatures likely gave rise to animals with hard body parts (skeletons) about 560 million years ago. Evolution of organisms has taken place in the last quarter of Earth’s history, which includes the Paleozoic, Mesozoic, and Cenozoic

Fossils from Bitter Springs Formation
 in Australia, oldest fossils known. 

Geologic time