Hadean Hadean History of operating systems Category="Geologic time scale"The name Hadean refers to a geologic period: the time before 3800 million years ago (mya). The Geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks. In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada and Western Australia. Some sources of information give other dates for the Hadean period ended.

W. B. Harland later coined an almost synonymous term: the "Priscoan period".

The oldest known rock formations comprise somewhat altered sediments from Greenland dated around 3800 mya by a volcanic dike that penetrated the rocks after they were deposited. Individual Zircon crystals redeposited in sediments in Western Canada and the Jack hills region of Western Australia are much older. The oldest dated zircons date from about 4400 mya - very close to the hypothesized time of the Earth's formation. The Greenland sediments include banded iron beds. They contain possibly Organic Carbon and quite possibly indicate that photosynthetic life had already emerged at that time. The oldest known fossils (from Australia) date from a few hundred million years later.

The etymology of the name "Hadean" (from Hades) suggests Underworld-like heat and confusion.

Precambrian 
Hadean eonArchean eonProterozoic eonPhanerozoic eon

Hadean eon
CrypticBasin GroupsNectarianLower Imbrian