Cambrian period


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Related to Cambrian period: Devonian period, Cambrian Explosion, Ordovician period, Silurian period

See also: Geologic Timescale (table)Geologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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Cambrian period

[Lat. Cambria=Wales], first period of the Paleozoic geologic era (see Geologic TimescaleGeologic Timescale
Era Period Epoch Approximate duration
(millions of years)
Approximate number of years ago
(millions of years)

Cenozoic Quaternary Holocene 10,000 years ago to the present  
Pleistocene 2 .
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, table) extending from approximately 570 to 505 million years ago. It was named by the 19th-century English geologist Adam Sedgwick, who first studied the great sequence of rocks characteristic of the period near Cambria, Wales. During the Cambrian, the continents and seas differed from present day configurations. Four major continents, Gondwanaland, Angara, and the two sections of Euramerica, were inundated with a rising sea level, accumulating thick sedimentary deposits (see sedimentsediment,
mineral or organic particles that are deposited by the action of wind, water, or glacial ice. These sediments can eventually form sedimentary rocks (see rock).
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). This sedimentary rock, i.e., conglomerate, sandstone, shale, and limestone, was formed in shallow seas that covered large areas of present-day North America, Europe, and Asia. In the United States, Lower Cambrian formations are found in the Appalachian; the sandstones near Waucoba Springs, S Calif.; and the thick layers of conglomerates and sandstones in Georgia, Tennessee, and North Carolina. Middle Cambrian rocks are found in New Brunswick, near Braintree, Mass. Upper Cambrian formations include the St. Croix sandstone of Wisconsin and the upper Mississippi valley, parts of the Arbuckle limestone of Oklahoma, and the Potsdam sandstone in New York's Adirondacks. In Russia, the Cambrian beds are remarkable in that they comprise mostly undisturbed and unconsolidated sand and clay despite their great age. The Cambrian rocks are the first rock layers to contain many easily recognizable fossils. The known Cambrian fauna—all marine—includes every phylum of invertebrates; the possibility that vertebrate fossils may be found cannot be excluded. The dominant animal was the trilobite, along with sea snails, brachiopods, sponges, and archaeocyathids. The ages of the various rock layers are distinguished according to the different genera of fossils they contain. The sudden appearance of highly developed and diversified fauna in Cambrian rock is best explained by the assumption that more primitive forms flourished during a missing stratigraphic interval between the close of the PrecambrianPrecambrian,
name of a major division of geologic time (see Geologic Timescale, table), from c.5 billion to 570 million years ago. It is now usually divided into the Archean and Proterozoic eons. Precambrian time includes 80% of the earth's history.
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 and the beginning of the Cambrian. Remnants of these early organisms were either destroyed by erosion or their soft bodies easily decayed in a short period of time. In addition, at the beginning of the Cambrian, numerous animals eventually developed skeletons, or hard parts, capable of leaving behind fossil remains.
References in periodicals archive ?
Palaeontologists believe a rise in global atmospheric oxygen some 750 million years ago made the 'explosion' of multicellular animals in the Cambrian period possible.
Yet this 530-million-year-old specimen from Earth's Cambrian period holds a special allure for paleontologists.
Until recently, paleontologists thought that the Ediacaran beings disappeared some tens of million of years before signs of complex, modern animals started appearing in the fossil record at the start of the Cambrian period, 543 million years ago.
Generations of scientists have portrayed vertebrates and their kin as an advanced group that arose only after most of the other broad animal groups had appeared in the riotous days of the Cambrian period.
The search for fossils from such ancient times, 60 million years before the Cambrian period and its burst of multicellular evolution, has yielded tantalizing bits but nothing with details like this specimen.
Although the evolutionary origins of fish and fishlike animals can be traced all the way back to the Cambrian Period (about 515 million years ago), those earliest primitive vertebrates were soft-bodied and lacked many of the features (including scales, bony bits, and jaws) that characterize the later fossil record.
Fossilized records from the Cambrian Period, which occurred between 540 million and 485 million years ago, provide glimpses into evolutionary biology when the world's ecosystems rapidly changed and diversified.
The evolutionary trend that led from large, apex predators to gentle, suspension-feeding giants during the highly productive Cambrian period is one that has also taken place several other times throughout Earth's history, according to lead author Dr Jakob Vinther, a lecturer in macroevolution at the University of Bristol.
Dozens of individual theories have been put forward over the past few decades for this rapid diversification of animal species in the early Cambrian Period of geological time.
A study by Paul Smith of Oxford University and David Harper of Durham University suggests that a combination of interlinking factors led to the rapid diversification of animal life during the Cambrian period.
The Cephalopod class, including squid, octopus and cuttlefish, a) is neurologically advanced, b) the same organ serves multiple functions, c) some mollusks contain pearls, purple dye and shells that humans value; and d) the Cephalopod class dates back to the Cambrian period 541 to 485 years ago.
Similarly, at the beginning of the Cambrian period, the author notes the emergence of another familiar aspect of the human race: consumer society.