The Cambrian explosion (also known as Cambrian radiation[1] or Cambrian diversification) is an interval of time beginning approximately 538.8 million years ago in the Cambrian period of the early Paleozoic, when a sudden radiation of complex life occurred and practically all major animalphyla started appearing in the fossil record.[2][3][4] It lasted for about 13[5][6][7] to 25[8][9] million years and resulted in the divergence of most modern metazoan phyla.[10] The event was accompanied by major diversification in other groups of organisms as well.[a]
Before early Cambrian diversification,[b] most organisms were relatively simple, composed of individual cells or small multicellular organisms, occasionally organized into colonies. As the rate of diversification subsequently accelerated, the variety of life became much more complex and began to resemble that of today.[12] Almost all present-day animal phyla appeared during this period,[13][14] including the earliest chordates.[15]
^Zhuravlev, Andrey; Riding, Robert (2000). The Ecology of the Cambrian Radiation. Columbia University Press. ISBN978-0-231-10613-9. The Cambrian radiation was the explosive evolution of marine life that started 550,000,000 years ago. It ranks as one of the most important episodes in Earth history. This key event in the history of life on our planet changed the marine biosphere and its sedimentary environment forever, requiring a complex interplay of wide-ranging biologic and nonbiologic processes.
^"Stratigraphic Chart 2022"(PDF). International Stratigraphic Commission. February 2022. Retrieved 22 April 2022.
^Maloof, A. C.; Porter, S. M.; Moore, J. L.; Dudas, F. O.; Bowring, S. A.; Higgins, J. A.; Fike, D. A.; Eddy, M. P. (2010). "The earliest Cambrian record of animals and ocean geochemical change". Geological Society of America Bulletin. 122 (11–12): 1731–1774. Bibcode:2010GSAB..122.1731M. doi:10.1130/B30346.1.
^Erwin, D. H.; Laflamme, M.; Tweedt, S. M.; Sperling, E. A.; Pisani, D.; Peterson, K. J. (2011). "The Cambrian conundrum: early divergence and later ecological success in the early history of animals". Science. 334 (6059): 1091–1097. Bibcode:2011Sci...334.1091E. doi:10.1126/science.1206375. PMID22116879. S2CID7737847.
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