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The Cambrian Portal

Introduction

The Cambrian ( /ˈkæmbri.ən, ˈkm-/ KAM-bree-ən, KAYM-) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordovician Period 485.4 Ma.

Most of the continents lay in the southern hemisphere surrounded by the vast Panthalassa Ocean. The assembly of Gondwana during the Ediacaran and early Cambrian led to the development of new convergent plate boundaries and continental-margin arc magmatism along its margins that helped drive up global temperatures. Laurentia lay across the equator, separated from Gondwana by the opening Iapetus Ocean. (Full article...)

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Artist's reconstruction of Waptia fieldensis.
Artist's reconstruction of Waptia fieldensis.
The small shelly fauna or small shelly fossils, abbreviated to SSF, are mineralized fossils, many only a few millimetres long, with a nearly continuous record from the latest stages of the Ediacaran to the end of the Early Cambrian period. They are very diverse, and there is no formal definition of "small shelly fauna" or "small shelly fossils". Almost all are from earlier rocks than more familiar fossils such as trilobites. Since most SSFs were preserved by being covered quickly with phosphate and this method of preservation is mainly limited to the Late Ediacaran and Early Cambrian periods, the animals that made them may actually have arisen earlier and persisted after this time span.

The bulk of the fossils are fragments or disarticulated remains of larger organisms, including sponges, molluscs, slug-like halkieriids, brachiopods, echinoderms, and onychophoran-like organisms that may have been close to the ancestors of arthropods. Although the small size and often fragmentary nature of SSFs makes it difficult to identify and classify them, they provide very important evidence for how the main groups of marine invertebrates evolved, and particularly for the pace and pattern of evolution in the Cambrian explosion. Besides including the earliest known representatives of some modern phyla, they have the great advantage of presenting a nearly continuous record of Early Cambrian organisms whose bodies include hard parts. (see more...)

Did you know...

Restoration of two Hurdia victoria
Restoration of two Hurdia victoria
  • ... that the 500-million-year-old Cambrian predator Hurdia was thought to be a number of separate organisms for 100 years, until the complete animal was reconstructed in March 2009?
  • ... that the shrimp-like 510-million-year-old arthropod Waptia was named after two mountains?
  • ... that Orsten, fossil-bearing lagerstätten in Sweden and elsewhere, are called "stinking stones" from organic content that has been preserved since the Cambrian Period?
  • ... that the fordilloid Camya asy is one of four accepted Cambrian bivalves?
  • ...that despite being known from many specimens, the fossil Fuxianhuia (pictured) remains one of the most controversial Cambrian arthropods?

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This trilobite species is Asaphiscus wheeleri.

Ventral view of Burgessia bella from Smithsonian Miscellaneous Collections, Volume 85, Number 3, Figure 3 (on page 16).
Photo credit: Charles Elmer Resser

Selected science, culture, and economics article

Burning oil shale.
Burning oil shale.
Oil shale, also known as kerogen shale, is an organic-rich fine-grained sedimentary rock containing kerogen (a solid mixture of organic chemical compounds) from which liquid hydrocarbons called shale oil can be produced. Shale oil is a substitute for conventional crude oil; however, extracting shale oil from oil shale is more costly than the production of conventional crude oil both financially and in terms of its environmental impact. Deposits of oil shale occur around the world. Estimates of global deposits range from 2.8 to 3.3 trillion barrels (450×10^9 to 520×10^9 m3) of recoverable oil.

Heating oil shale to a sufficiently high temperature causes the chemical process of pyrolysis to yield a vapor. Upon cooling the vapor, the liquid shale oil—an unconventional oil—is separated from combustible oil-shale gas (the term shale gas can also refer to gas occurring naturally in shales). Oil shale can also be burned directly in furnaces as a low-grade fuel for power generation and district heating or used as a raw material in chemical and construction-materials processing.

Oil-shale mining and processing raise a number of environmental concerns, such as land use, waste disposal, water use, waste-water management, greenhouse-gas emissions and air pollution. Estonia and China have well-established oil shale industries, and Brazil, Germany, and Russia also utilize oil shale. (see more...)

Quality Content

Featured Cambrian articles - None
Good Cambrian articles - Fossils of the Burgess Shale - Opabinia - Small shelly fauna - Stephen Jay Gould - Waptia

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