Precambrian

*Precambrian*
Precambrian
Chronology
−4500 — – — – −4000 — – — – −3500 — – — – −3000 — – — – −2500 — – — – −2000 — – — – −1500 — – — – −1000 — – — – −500 — – — – 0 —	Precambrian Hadean Archean Proterozoic Phaner-; ozoic Eoarchean Paleoarchean Mesoarchean Neoarchean Paleoproterozoic Mesoproterozoic Neoproterozoic Paleozoic Mesozoic Cenozoic
	Vertical axis scale: Millions of years ago
Proposed subdivisions	See Proposed Precambrian timeline;
Etymology
Synonym(s)	Cryptozoic;
Usage information
Celestial body	Earth
Regional usage	Global (ICS)
Time scale(s) used	ICS Time Scale
Definition
Chronological unit	Supereon
Stratigraphic unit	Supereonthem
Time span formality	Informal
Lower boundary definition	Formation of the Earth
Lower GSSA ratified	October 5, 2022
Upper boundary definition	Appearance of the Ichnofossil Treptichnus pedum
Upper boundary GSSP	Fortune Head section, Newfoundland, Canada; 47°04′34″N 55°49′52″W / 47.0762°N 55.8310°W
Upper GSSP ratified	August 1992 (as base of Cambrian)

The Precambrian ( /priˈkæmbri.ən, -ˈkeɪm-/ pree-KAM-bree-ən, -⁠KAYM-; pre-Cambrian, or Cryptozoic, sometimes abbreviated pꞒ or PreꞒ) 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 Latinized 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, 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.