Description
Stromatolites are a type of sedimentary rock that is often highly layered and contains a high amount of lime. They form when cyanobacteria capture and hold the sediment. These then form layer upon layer in a manner similar to how coral reefs form. Stromatolites are among the oldest fossils, found from approximately 3.5 billion years ago. They were common in the Precambrian, but today they are only found in a few special environments, particularly in places where the water is very salty or alkaline. This is because in normal environments, a stromatolite would be decomposed by animals much faster than it can be built up. A well-known location for stromatolites is Shark Bay in Western Australia.
Stromatolite
