Cambrian

The Cambrian was a geological period and the earliest of the eras of the Phanerozoic Eon. It began approximately 539 million years ago and ended approximately 485 million years ago. Before the Cambrian came a long period called the Precambrian, which marked the beginning of life on Earth.

The name derives from "Cambria," a Latin name for Wales (United Kingdom). Rocks from this period were first studied there, and the period was named by a British geologist in the nineteenth century.

The Cambrian Explosion of Life

The defining feature of this period was the sudden appearance of many animal types over a geologically short span of time. This is known as the "Cambrian explosion." Most of the major groups of animals alive today (phyla) first appear in the fossil record during this period. Proposed explanations include rising oxygen levels in the oceans, changes in ocean chemistry that enabled the formation of hard shells, and predator-prey interactions that drove the evolution of defense mechanisms.

Notable Fossils

Trilobites were marine animals with shells that were extremely abundant in Cambrian rocks and are used to distinguish different layers. Some of the most famous fossil sites include the Burgess Shale in Canada and Chengjiang in China, which preserve soft-bodied animals that lacked hard shells.

Geography and Climate

During this period the continents were positioned differently from today. A large continent called Gondwana had gathered in the south. Sea levels were generally higher, which flooded large portions of the continents and created shallow seas suitable for abundant life. Land was barren, lacking higher plants; most life was confined to the waters.