Topic summary
Stromatolites
Extracted from the Wikipedia article Stromatolite.
Fossil record
Stromatolites are a major constituent of the fossil record of the first forms of life on Earth. They peaked about 1.25 billion years ago (Ga) and subsequently declined in abundance and diversity, so that by the start of the Cambrian they had fallen to 20% of their peak. The most widely supported explanation is that stromatolite builders fell victim to grazing creatures (the Cambrian substrate revolution); this theory implies that sufficiently complex organisms were common around 1 Ga. Another hypothesis is that protozoa such as foraminifera were responsible for the decline, favoring formation of thrombolites over stromatolites through microscopic bioturbation.