Precambrian

Precambrian
Chronology
Proposed subdivisionsSee Proposed Precambrian timeline
Etymology
Synonym(s)Cryptozoic
Usage information
Celestial bodyEarth
Regional usageGlobal (ICS)
Time scale(s) usedICS Time Scale
Definition
Chronological unitSupereon
Stratigraphic unitSupereonthem
Time span formalityInformal
Lower boundary definitionFormation of the Earth
Lower GSSA ratifiedOctober 5, 2022[1]
Upper boundary definitionAppearance of the Ichnofossil Treptichnus pedum
Upper boundary GSSPFortune Head section, Newfoundland, Canada
47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W / 47.0762; -55.8310
Upper GSSP ratified1992

The Precambrian ( /priˈkæmbri.ən, -ˈkm-/ pree-KAM-bree-ən, -⁠KAYM-;[2] or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the Phanerozoic Eon, which is named after Cambria, the Latinised name for Wales, where rocks from this age were first studied. The Precambrian accounts for 88% of the Earth's geologic time.

The Precambrian is an informal unit of geologic time,[3] subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago (Ga) to the beginning of the Cambrian Period, about 538.8 million years ago (Ma), when hard-shelled creatures first appeared in abundance.

  1. ^ Cohen, Kim. "New edition of the Chart - 2022-10". International Commission on Stratigraphy. Retrieved 16 January 2023.
  2. ^ "Precambrian". CollinsDictionary.com. HarperCollins. Retrieved 2023-08-30.
  3. ^ Gradstein, F.M.; Ogg, J.G.; Schmitz, M.D.; Ogg, G.M., eds. (2012). The Geologic Timescale 2012. Vol. 1. Elsevier. p. 301. ISBN 978-0-44-459390-0.