Few fossils are present in Precambrian rock. The earliest life forms probably did not produce hard parts that fossilized. Most of the remaining Precambrian rock is igneous (of volcanic origin) or metamorphic and would not preserve fossils.
Yet recently Australian formations 3,500 million years old have been identified as traces of ancient life. These are "stromatolites," layered dome-shaped structures similar to structures that are formed of minerals trapped by some mat-forming colonies of algae in modern times.