Cambrian explosion
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The Cambrian explosion is an interval of time approximately 538.8 million years ago in the Cambrian period of the early Paleozoic when there was a sudden radiation of complex life, and practically all major animal phyla started appearing in the fossil record. It lasted for about 13 to 25 million years and resulted in the divergence of most modern metazoan phyla. The event was accompanied by major diversification in other groups of organisms as well.
Rusophycus and other trace fossils from the Gog Group, Middle Cambrian, Lake Louise, Alberta, Canada
Stromatolites (Pika Formation, Middle Cambrian) near Helen Lake, Banff National Park, Canada
Modern stromatolites in Hamelin Pool Marine Nature Reserve, Western Australia
An Ediacaran trace fossil, made when an organism burrowed below a microbial mat.
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. Its subdivisions, and its base, are somewhat in flux.
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