Agnostida is an order of arthropod which first developed near the end of the Early Cambrian period and thrived during the Middle Cambrian.

Owing to the complete absence of mountain building and glaciation since the Permian ( in many areas since the Cambrian ) ages, the outback is extremely rich in iron, aluminium, manganese and uranium ores, and also contains major deposits of gold, nickel, iron, lead and zinc ores.

At ( Middle Cambrian ) old it is one of the earliest fossil beds containing the imprints of soft-parts.

This is mainly due to the limited extent of burrowing activity ; as such bioturbation became more prevalent throughout the Cambrian, environments capable of preserving organisms ' soft parts became much rarer.

The Cambrian is unique in its unusually high proportion of lagerstätten.

The base of the Cambrian is defined on a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.

Nevertheless, the usage of Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, for the stratigraphic detection of this boundary is always risky because of occurrence of very similar trace fossils belonging to the Treptichnids group well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western USA.

The Cambrian period follows the Ediacaran and is followed by the Ordovician period.

The Cambrian is divided into four epochs or series and ten ages or stages.

In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian ( Caerfai or Waucoban, mya ), Middle Cambrian ( St Davids or Albertian, mya ) and Furongian ( mya ; also known as Late Cambrian, Merioneth or Croixan ).

The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:

The Ediacaran Period, named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon.

The GSSP of the upper boundary of the Ediacaran is the lower boundary of the Cambrian on the SE coast of Newfoundland approved by the International Commission on Stratigraphy as a preferred alternative to the base of the Tommotian Stage in Siberia which was selected on the basis of the ichnofossils Treptichnus pedum.

As to the Treptichnus pedum, a reference ichnofossil for the lower boundary of the Cambrian, its usage for the stratigraphic detection of this boundary is always risky because of the occurrence of very similar trace fossils belonging to the Treptichnids group well below the T. pedum in Namibia, Spain and Newfoundland, and possibly, in the western United States.

The age of the top is the same as the widely recognised age for the base of the Cambrian Period 542 ± 0. 3 Mya ( million years ago ).< ref name = Amthor2003 >

They bear little resemblance to modern lifeforms, and their relationship even with the later lifeforms of the Cambrian explosion is difficult to interpret.

An example of modern paleontological progress is the application of synchrotron X-ray tomographic techniques to early Cambrian bilaterian embryonic microfossils that has recently yielded new insights of metazoan evolution at its earliest stages.

A continuous section is available from beds that are clearly Precambrian into beds that are clearly Cambrian.

Mineralized skeletons of bryozoans first appear in rocks from latest Cambrian period, about, making it the last major phylum to appear in the fossil record.

The first vertebrates appeared over 500 million years ago ( Mya ), during the Cambrian period, and may have resembled the modern hagfish in form.

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 arthropods.

The first dramatic rise in atmospheric oxygen on Earth, to about a tenth of its present-day value, occurred approximately 2. 5 billion years ago, and that level did not change significantly until the Cambrian era approximately 600 million years ago.

* 542 ± 0. 3 Ma: Cambrian explosion – vast multiplication of hard-bodied life ; first abundant fossils ; start of the Paleozoic

The Cambrian Period witnessed the most rapid and widespread diversification of life in Earth's history, known as the Cambrian explosion, in which most modern phyla first appeared.

The early Cambrian climate was probably moderate at first, becoming warmer over the course of the Cambrian, as the second-greatest sustained sea level rise in the Phanerozoic got underway.

It spans from the formation of Earth about 4570 Ma ( million years ) ago to the beginning of the Cambrian Period, about 542 Ma, when macroscopic hard-shelled animals first appeared in abundance.

The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the classical name for Wales, where rocks from this age were first studied.

Its name derives from the Ancient Greek words and, meaning visible life, since it was once believed that life began in the Cambrian, the first period of this eon.

Aside from the hard-to-classify Arkarua ( a Precambrian animal with Echinoderm-like pentamerous radial symmetry ), the first definitive members of the phylum appeared near the start of the Cambrian period.

Although corals first appeared in the Cambrian period, some, fossils are extremely rare until the Ordovician period, 100 million years later, when rugose and tabulate corals became widespread.

They originated as marine animals, possibly in the Cambrian period, but the first confirmed chelicerate fossils, eurypterids, date from in the Late Ordovician period.

The first group of cratons would eventually, around 550 million years ago ( on the boundary between the Ediacaran and Cambrian ), fuse again with Amazonia, West Africa and the Rio de la Plata craton.

Classically, the boundary between the Proterozoic and the Phanerozoic eons was set at the base of the Cambrian period when the first fossils of animals including trilobites and archeocyathids appeared.

The name first appears in 1795 in William Owen Pughe's Cambrian Register: " The Mabinogion, or Juvenile Amusements, being Ancient Welsh Romances.

Mineralized exoskeletons first appeared in the fossil record about, and their evolution is considered by some to have played a role in the subsequent Cambrian explosion of animals.

Lagerstätten span geological time from the Cambrian period to the present.

* Welsh Basin, a basin during the Cambrian, Ordovician and Silurian geological periods

He is best known for pioneering faunal analysis of Silurian beds by means of index fossils, especially graptolites, and his proposal ( eventually adopted ) that the beds between the Cambrian beds of north Wales and the Silurian beds of South Wales should be assigned to a new geological period: the Ordovician.

Dinoflagellates are represented by fossil dinocysts, which have a long geological record with lowest occurrences during the mid-Triassic., whilst geochemical markers suggest a presence to the Early Cambrian

It is also used in geology to denote the geologic period between around 542 million years and 488. 3 million years ago ; in 1835 the geologist Adam Sedgwick named this geological period the Cambrian, after studying rocks of that age in Wales.

Lagerstätten span geological time from the Cambrian period to the present.

The chief geological investigation of the last decade of his life was devoted to the Highlands of Scotland, where he wrongly believed he had succeeded in showing that the vast masses of crystalline schists, previously supposed to be part of what used to be termed the Primitive formations, were really not older than the Silurian period, for that underneath them lay beds of limestone and quartzite containing Lower Silurian ( Cambrian ) fossils.

The formation is of particular interest because it appears to cover the boundary between the problematic organisms of the Ediacaran geological period and the more familiar fauna of the Cambrian explosion of lifeforms whose descendents are recognizable.

The island's oldest geological formation, Gunung Matchincang, was the first part of South-East Asia to rise from the seabed in the Cambrian period more than half a billion years ago.

They cite the Cambrian explosion — the appearance of abundant fossils in the upper Ediacaran ( Vendian ) Period and lower Cambrian Period — as the pre-Flood / Flood boundary, the presence in such sediments of fossils that do not occur later in the geological record as part of a pre – flood biota that perished and the absence of fossilized organisms that appear later, such as angiosperms and mammals, as due to erosion of sediments deposited by the flood as waters receded off the land.

* Albertan epoch, alternate name for the Middle Cambrian geological epoch

The game is divided into five distinct geological periods: the Cambrian Period and the Ordovician Period of the Paleozoic Era (" The World Before Land ") from 500 million years ago to 450 million years ago, then the Carboniferous period (" Early Creatures of Land "), the Mesozoic Era (" Age of Dinosaurs "), the late Neogene period (" Ice Age "), and finally the early Neogene period (" Early Man ").

The classical name for Wales, Cambria ( derived from Cymru ), gave its name to the earliest geological period of the Paleozoic era, the Cambrian.

The geological structure is complex with the peninsula's soils dating to the middle Cambrian to early Ordovician continental margin, creating a carbonate platform of limestone, shale, and sandstone.

The island has rock dating back to late Cambrian and the eastern parts is littered with erratic boulders deposited during the last Ice Age, thus the island illustrate well the local geological events spanning half a billion years.

The Lost Soldier Field in Wyoming has oil pools, he stated, at every horizon of the geological section, from the Cambrian sandstone overlying the basement to the upper Cretaceous deposits.