Cambrian period


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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 ?
The appearance of the vertical burrow Treptichnus pedum was recognized by the International Commission on Stratigraphy during the 1990s as the boundary marker for the beginning of the Cambrian period.
The animals that appeared during the Cambrian period paved the pathway toward our modern ecosystems.
Combining fossil dates and the DNA analysis, Peterson, Erwin and their colleagues conclude that the basic genetic tools for fancy animal bodies arose long before a surge of evolutionary innovation around the Cambrian period gave rise to modern animal groups.
Kooteninchela deppi is helping researchers to piece together more information about life on Earth during the Cambrian period when nearly all modern animal types emerged.
Early in the Cambrian period, which began about 542 million years ago, most multicellular animals had soft bodies that didn't fossilize well.
Although the precise identity of the tracemakers remains elusive, the structures bear several striking similarities with a cone-shaped organism called Conichnus that has been found in the Cambrian period.
Our description of Spartobranchus tenuis, a creature previously unknown to science, pushes the fossil record of the enteropneusts back 200 million years to the Cambrian period, fundamentally changing our understanding of biodiversity from this period," he added.
The rocks bearing the fossils were deposited on an ocean bottom about 520 million years ago during the Cambrian period.
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.
However this reinterpretation of Cotyledion tylodes as an entoproct places the fossil record of this group in the earlier Cambrian period.
Evolution's Big Bang took place beginning 543 million years ago, in the Cambrian period.
Research published in the journal Current Biology shows that evolution's "Big Bang" during the Cambrian period between 540 and 520 million years ago can be explained scientifically and fits in with Darwin's theory of natural selection, scientists have said.