Книга: Precambrian: Phanerozoic, Geologic Time Scale, Biostratigraphy, History of the Earth, Metamorphic Rock, Planetesimal, Paleontology, Eon, Deprecation, Proterozoic, Glacial Period, Cryogenian

High Quality Content by WIKIPEDIA articles! 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 4500 Ma (million years ago) to the beginning of the Cambrian Period, when macroscopic hard-shelled animals first appeared in abundance about 542 Ma. The Precambrian is so named because it precedes the Cambrian, the first period of the Phanerozoic Eon, which is named after the Roman name for Wales, Cambria, where rocks from this age were first studied. The Precambrian period accounts for 87% of geologic time.