related topics
{island, water, area}
{specie, animal, plant}
{acid, form, water}
{math, energy, light}
{language, word, form}
{album, band, music}
{day, year, event}

The Precambrian (Pre-Cambrian) is an informal name for the span of time before the current Phanerozoic Eon, and is divided into several eons of the geologic time scale. It spans from the formation of Earth around 4600 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 the classical name for Wales, Cambria, where rocks from this age were first studied. The Precambrian accounts for 85% of geologic time.



Very little is known about the Precambrian, despite it making up roughly seven-eighths of the Earth's history, and what little is known has largely been discovered in the past fifty years. The Precambrian fossil record is poor, and those fossils present (e.g. stromatolites) are of limited biostratigraphic use.[1] Many Precambrian rocks are heavily metamorphosed, obscuring their origins, while others have either been destroyed by erosion, or remain deeply buried beneath Phanerozoic strata.[2][3]

It is thought that the Earth itself coalesced from material in orbit around the Sun roughly 4500 Ma and may have been struck by a very large (Mars-sized) planetesimal shortly after it formed, splitting off material that came together to form the Moon (see Giant impact theory). A stable crust was apparently in place by 4400 Ma, since zircon crystals from Western Australia have been dated at 4404 Ma.[4]

The term Precambrian is somewhat out-moded, but is still in common use among geologists and paleontologists. It was briefly also called the Cryptozoic eon. It seems likely that it will eventually be replaced by the preferred terms Proterozoic, Archaean, and Hadean, and become a deprecated term. (See geologic time scale.)

Full article ▸

related documents
Neotropic ecozone
Brackish water
Cretaceous–Tertiary extinction event
Ellesmere Island
Deccan Traps
Geography of Zimbabwe
Geography of Saint Pierre and Miquelon
Geography of Malawi
Geography of Togo
Lake Taupo
Malham Cove
Mid-Atlantic Ridge
Geology of Victoria
Meteor Crater
Medieval Warm Period
Clipperton Island
Olympus Mons
Year Without a Summer
Broome, Western Australia