AskDefine | Define Cambrian

Dictionary Definition

Cambrian adj : of or relating to or characteristic of Wales or its people or their language; "the Welsh coast"; "Welsh syntax" [syn: Welsh]

Noun

1 from 544 million to about 500 million years ago; marine invertebrates [syn: Cambrian period]
2 a native or resident of Wales [syn: Welshman, Welsh]

User Contributed Dictionary

English

Adjective

  1. of a geologic period within the Paleozoic era; comprises lower, middle and Furongian epochs from about 542 to 490 million years ago
  2. of, or relating to Wales

Noun

Cambrian
  1. the Cambrian period
  2. a Welsh person

See also

Extensive Definition

The Cambrian is a geologic period and system that began about period start Cambrianperiod start error cambrian Ma (million years ago) at the end of the Proterozoic eon and ended about period end cambrianperiod start error ordovician Ma with the beginning of the Ordovician period . It was the first period of the Paleozoic era of the Phanerozoic eon. The Cambrian takes its name from Cambria, the classical name for Wales, the area where rocks from this time period were first studied.
The Cambrian is the earliest period in whose rocks are found numerous large, distinctly fossilizable multicellular organisms. This sudden appearance of hard body fossils is referred to as the Cambrian explosion. Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks it was not until 1994 that this time period was internationally ratified. The base of the Cambrian is defined on a complex assemblage of trace fossils known as the Trichophycus pedum assemblage. This assemblage is distinct from anything in the Precambrian as it has ecologically tiered vertical burrows which are absent from the Precambrian.

Cambrian subdivisions

The Cambrian period follows the Ediacaran and is followed by the Ordovician period. The Cambrian is divided into three epochs — the Early Cambrian (Caerfai or Waucoban), Middle Cambrian (St Davids or Albertian) and Furongian (also known as Late Cambrian, Merioneth or Croixan). Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
Each of the epochs are divided into several stages. Only one, the Paibian, has been recognized by the International Commission on Stratigraphy, and others are still unnamed. However, the Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

Cambrian dating

The time range for the Cambrian has classically been thought to have been from about 500 mya to about 570 mya. The lower boundary of the Cambrian was traditionally set at the earliest appearance of early arthropods known as trilobites and also unusual forms known as archeocyathids (literally 'ancient cup') that are thought to be the earliest sponges and also the first non-microbial reef builders.
The end of the period was eventually set at a fairly definite faunal change now identified as an extinction event. Fossil discoveries and radiometric dating in the last quarter of the 20th century have called these dates into question. Date inconsistencies as large as 20 Ma are common between authors. Framing dates of ca. () 545 to 490 mya were proposed by the International Subcommission on Global Stratigraphy as recently as 2002.
A radiometric date from New Brunswick puts the end of the first stage of the Cambrian around 511 mya. This leaves 21 Ma for the other two stages of the Cambrian.
A more precise date of 542 ± 0.3 mya for the extinction event at the beginning of the Cambrian has recently been submitted. The rationale for this precise dating is interesting in itself as an example of paleological deductive reasoning. Exactly at the Cambrian boundary there is a marked fall in the abundance of carbon-13, a "reverse spike" that paleontologists call an excursion. It is so widespread that it is the best indicator of the position of the Precambrian-Cambrian boundary in stratigraphic sequences of roughly this age. One of the places that this well-established carbon-13 excursion occurs is in Oman. Amthor (2003) describes evidence from Oman that indicates the carbon-isotope excursion relates to a mass extinction: the disappearance of distinctive fossils from the Precambrian coincides exactly with the carbon-13 anomaly. Fortunately, in the Oman sequence, so too does a volcanic ash horizon from which zircons provide a very precise age of 542 ± 0.3 Ma (calculated on the decay rate of uranium to lead). This new and precise date tallies with the less precise dates for the carbon-13 anomaly, derived from sequences in Siberia and Namibia. It is presented here as likely to become accepted as the definitive age for the start of the Phanerozoic eon, and thus the start of the Paleozoic era and the Cambrian period.

Cambrian paleogeography

Cambrian continents are thought to have resulted from the breakup of a Neoproterozoic supercontinent called Pannotia. The waters of the Cambrian period appear to have been widespread and shallow. Gondwana remained the largest supercontinent after the breakup of Pannotia. It is thought that Cambrian climates were significantly warmer than those of preceding times that experienced extensive ice ages discussed as the Varanger glaciation. Also there was no glaciation at the poles. Continental drift rates in the Cambrian may have been anomalously high. Laurentia, Baltica and Siberia remained independent continents since the break-up of the supercontinent of Pannotia. Gondwana started to drift towards the South Pole. Panthalassa covered most of the southern hemisphere, and minor oceans included the Proto-Tethys Ocean, Iapetus Ocean, and Khanty Ocean, all of which expanded by this time.

Cambrian fauna

Of those modern animal phyla that fossilize easily, all save the bryozoans have claimed representatives in the Cambrian. Many extinct phyla and odd animals that have unclear relationships to other animals also appear in the Cambrian. The apparent "sudden" appearance of very diverse faunas over a period of no more than a few tens of millions of years is referred to as the "Cambrian Explosion". Also, the first possible tracks on land, such as Protichnites and Climactichnites, dating to about 530 mya and found in Ontario, Canada, and northern United States, appeared at this time. The conodonts, small predatory primitive chordates known from their fossilised teeth, also appeared during the Furongian epoch of the Cambrian period. The conodonts thrived throughout the Paleozoic and the early Mesozoic until they completely disappeared during the Late Triassic period when the first mammals were evolving.
The best studied sites where the soft parts of organisms have fossilized are in the Burgess shale of British Columbia. They represent strata from the Middle Cambrian and provide us with a wealth of information on early animal diversity. Similar faunas have subsequently been found in a number of other places — most importantly in very early Cambrian shales in the People's Republic of China's Yunnan Province (see Maotianshan shales). Fairly extensive Precambrian Ediacaran faunas have been identified in the past 50 years, but their relationships to Cambrian forms are quite obscure.

Cambrian flora

Generally it is accepted that there were no land plants at this time although molecular dating suggests that land plant ancestors diverged from the algae much earlier, in the Neoproterozoic about 700 ma, and that fungi diverged from the animals about 1 billion years ago. The land at this time was barren, mostly desert and badlands.

References

Cambrian in Arabic: عصر كامبري
Cambrian in Breton: Kambrian
Cambrian in Catalan: Cambrià
Cambrian in Czech: Kambrium
Cambrian in Welsh: Cambriaidd
Cambrian in Danish: Kambrium
Cambrian in German: Kambrium
Cambrian in Estonian: Kambrium
Cambrian in Modern Greek (1453-): Κάμβρια περίοδος
Cambrian in Spanish: Cámbrico
Cambrian in Esperanto: Kambrio
Cambrian in Basque: Kanbriar
Cambrian in Persian: کامبرین
Cambrian in French: Cambrien
Cambrian in Galician: Cámbrico
Cambrian in Korean: 캄브리아기
Cambrian in Indonesian: Kambrium
Cambrian in Icelandic: Kambríumtímabilið
Cambrian in Italian: Cambriano
Cambrian in Hebrew: קמבריון
Cambrian in Georgian: კამბრიული სისტემა
Cambrian in Kazakh: Кембрий
Cambrian in Latin: Aevum Cambricum
Cambrian in Luxembourgish: Kambrium
Cambrian in Lithuanian: Kambras
Cambrian in Hungarian: Kambrium
Cambrian in Dutch: Cambrium
Cambrian in Japanese: カンブリア紀
Cambrian in Norwegian: Kambrium
Cambrian in Polish: Kambr
Cambrian in Portuguese: Cambriano
Cambrian in Romanian: Cambrian
Cambrian in Russian: Кембрий
Cambrian in Simple English: Cambrian
Cambrian in Slovak: Kambrium
Cambrian in Slovenian: Kambrij
Cambrian in Serbo-Croatian: Kambrij
Cambrian in Finnish: Kambrikausi
Cambrian in Swedish: Kambrium
Cambrian in Vietnamese: Kỷ Cambri
Cambrian in Turkish: Kambriyen dönem
Cambrian in Ukrainian: Кембрійський період
Cambrian in Volapük: Kambrium
Cambrian in Chinese: 寒武纪
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