Hadean

related topics
{acid, form, water}
{island, water, area}
{math, energy, light}
{god, call, give}
{day, year, event}

The Hadean (pronounced /ˈheɪdiən/) is the geologic eon before the Archean. It started at Earth's formation about 4.6 billion years ago (4,600 Ma), and ended roughly 3.8 billion years ago, though the latter date varies according to different sources. The name "Hadean" derives from Hades, Greek for "Underworld", referring to the conditions on Earth at the time. The geologist Preston Cloud coined the term in 1972, originally to label the period before the earliest-known rocks. W. Brian Harland later coined an almost synonymous term: the "Priscoan period". Other older texts simply refer to the eon as the Pre-Archean.

Contents

Subdivisions

Since few geological traces of this period remain on Earth there are no official subdivisions. However, several major divisions of the Lunar geologic timescale occurred during the Hadean, and so these are sometimes used unofficially to refer to the same periods of time on Earth.

The Lunar divisions are:

Hadean rocks

In the last decades of the 20th century geologists identified a few Hadean rocks from Western Greenland, Northwestern Canada and Western Australia. Rock formations in Greenland comprise sediments dated around 3.8 billion years ago and are somewhat altered 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 4,400 Ma[1] – very close to the hypothesized time of the Earth's formation.

The Greenland sediments include banded iron beds. They contain possibly organic carbon and imply some possibility that photosynthetic life had already emerged at that time. The oldest known fossils (from Australia) date from a few hundred million years later.

Full article ▸

related documents
Marl
Limonite
Slurry pipeline
Contrail
Ulexite
Octahedrite
Ununennium
Isoleucine
Uraninite
Phenyl group
Potassium ferrocyanide
Weatherization
Perlite
Surfactant
Coenzyme A
Thermal diffusivity
Calamine (mineral)
List of synthetic polymers
Hypoxanthine
Chemisorption
Leucine
Valine
Soman
Periodic table (standard)
Diene
Putrescine
Aquamarine
Northern blot
Inositol triphosphate
Vitamin E