Prehistoric life
The Cambrian is famed for its explosion of abundant and diverse life forms. Life had diversified into many forms and many ways of living: animals now swam, crawled, burrowed, hunted, defended themselves and hid away. Some creatures had evolved hard parts such as shells, which readily fossilised and left a clear record behind. However, sometimes geologists get lucky and find beautiful fossils of soft and squishy creatures - as at the Burgess Shale site. In Cambrian times there was no life on land and little or none in freshwater - the sea was still very much the centre of living activity.
Began: 545 million years ago
Ended: 495 million years ago
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The Cambrian explosion
Could the rise of creatures with eyes have caused an evolutionary arms race?
Professor Brian Cox visits the Burgess Shale, a very important fossil field in Yoho National Park in the Canadian Rocky Mountains. The fossils record the explosion of life that started about 540 million years ago during the Cambrian period. He explains a speculative theory that the evolution of creatures with eyes, such as trilobites, triggered the evolution of more complex forms of life.
Pre-Cambrian Wales
Undulating rocks tell of a time when Wales was underwater.
Undulating rocks tell of a time when Wales was underwater.
Reconstruction of the Earth in the Cambrian period, 545 million - 495 million years ago. Credit: Dr Ron Blakey, NAU Geology.
During this period the following extinction level events are thought to have occurred.
Flood basalt eruptionsThe Cambrian is the first geological period of the Paleozoic Era, lasting from 541.0 ± 1.0 to 485.4 ± 1.9 million years ago (mya) and is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's Cambrian rocks are best exposed. The Cambrian is unique in its unusually high proportion of lagerstätten. These are sites of exceptional preservation, where 'soft' parts of organisms are preserved as well as their more resistant shells. This means that our understanding of the Cambrian biology surpasses that of some later periods.
The Cambrian Period marked a profound change in life on Earth; prior to the Cambrian, living organisms on the whole were small, unicellular and simple. Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common. The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of many modern phyla, representing the evolutionary stems of modern groups of species, such as the molluscs and arthropods.[citation needed] While diverse life forms prospered in the oceans, the land was comparatively barren – with nothing more complex than a microbial soil crust and a few molluscs that emerged to browse on the microbial biofilm Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.
The United States Federal Geographic Data Committee uses a "barred capital C" character similar to the capital letter Ukrainian Ye ‹Є› to represent the Cambrian Period. The properUnicode character is U+A792 Ꞓ latin capital letter c with bar.
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Goose barnacles
Snails and slugs
Jellyfish
Trilobites
