== Oldest fossil ==
The oldest fossil ever discovered that scientists agree on is that of prokaryotes of approximately 2.5 billion years old found in the Gunflint Chert of Western Ontario. There are some debated fossils from the Apex Chert in Australia that are about 3.4 billion years old. These fossils already show well-developed organisms, suggesting that life had already existed for a while.
The oldest eukaryotes are red alga fossils that are dated to about 1.2 billion years.