The oldest fossils found on Earth are located in Western Australia. They are stromatolites, which are layered mounds of calcium carbonate built up by cyanobacteria. These fossils have been dated back to 3.48 billion years old and are found in the Pilbara Craton.

While the Pilbara Craton holds the oldest fossils, there are other regions where ancient fossils can be found:

* Greenland: Contains fossils around 3.7 billion years old, which are debated as to their biological origin.

* South Africa: Hosts fossilized microbial mats from the Barberton Greenstone Belt, dating back to about 3.5 billion years ago.

It's important to remember that the oldest fossils are extremely rare and often very small and difficult to identify. Scientists continue to search for even older fossils, pushing back the timeline of life on Earth.