The Cambrian Period (/ˈkæmbri.ən,ˈkeɪm-/KAM-bree-ən, KAYM-; sometimes symbolized Ꞓ) 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 million years ago (mya) to the beginning of the Ordovician Period 485.4 mya. Its subdivisions, and its base, are somewhat in flux. The period was established as "Cambrian series" by Adam Sedgwick, who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization. The Cambrian is unique in its unusually high proportion of lagerstätte sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.
^Sedgwick and R. I. Murchison (1835) "On the Silurian and Cambrian systems, exhibiting the order in which the older sedimentary strata succeed each other in England and Wales," Notices and Abstracts of Communications to the British Association for the Advancement of Science at the Dublin meeting, August 1835, pp. 59–61, in: Report of the Fifth Meeting of the British Association for the Advancement of Science; held in Dublin in 1835 (1836). From p. 60: "Professor Sedgwick then described in descending order the groups of slate rocks, as they are seen in Wales and Cumberland. To the highest he gave the name of Upper Cambrian group. ... To the next inferior group he gave the name of Middle Cambrian. ... The Lower Cambrian group occupies the S.W. coast of Cærnarvonshire,"
^Maloof, Adam C.; Rose, Catherine V.; Beach, Robert; Samuels, Bradley M.; Calmet, Claire C.; Erwin, Douglas H.; Poirier, Gerald R.; Yao, Nan; Simons, Frederik J. (17 August 2010). "Possible animal-body fossils in pre-Marinoan limestones from South Australia". Nature Geoscience. 3 (9): 653–659. Bibcode:2010NatGe...3..653M. doi:10.1038/ngeo934.