Microbial mat
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A microbial mat is a multi-layered sheet of microorganisms, mainly bacteria and archaea, or bacteria alone. Microbial mats grow at interfaces between different types of material, mostly on submerged or moist surfaces, but a few survive in deserts. A few are found as endosymbionts of animals.
The cyanobacterial algal mat, salty lake on the White Sea seaside
Stromatolites are formed by some microbial mats as the microbes slowly move upwards to avoid being smothered by sediment.
Kinneyia-like structure in the Grimsby Formation (Silurian) exposed in Niagara Gorge, New York
Blister-like microbial mat on ripple-marked surface of a Cambrian tidal flat at Blackberry Hill, Wisconsin
Cambrian
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The Cambrian is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran period 538.8 Ma to the beginning of the Ordovician Period 485.4 Ma.
Archeocyathids from the Poleta formation in the Death Valley area
Stromatolites of the Pika Formation (Middle Cambrian) near Helen Lake, Banff National Park, Canada
Trilobites, like these Elrathia kingii were very common arthropods during this time
Pikaia was a stem-chordate from the Middle Cambrian