![Garnet paragneiss Nuvvuagittuq Greenstone Belt, 4](https://upload.wikimedia.org/wikipedia/commons/c/c9/Garnet_paragneiss_Nuvvuagittuq_Greenstone_Belt%2C_4.28_Ga.jpg)
The Eoarchean (; also spelled Eoarchaean) is the first
era
An era is a span of time defined for the purposes of chronology or historiography, as in the regnal eras in the history of a given monarchy, a calendar era used for a given calendar, or the geological eras defined for the history of Earth.
Comp ...
of the
Archean
The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth
Earth ...
Eon of the
geologic record
The geologic record in stratigraphy, paleontology and other natural sciences refers to the entirety of the layers of rock strata. That is, deposits laid down by volcanism or by deposition of sediment derived from weathering detritus (clays, sand ...
. It spans 400 million years, from the end of the Hadean Eon 4 billion years ago (4000
Mya) to the start of the
Paleoarchean
The Paleoarchean (), also spelled Palaeoarchaean (formerly known as early Archean), is a Geologic time scale#Terminology, geologic era within the Archean, Archaean Eon. The name derives from Greek "Palaios" ''ancient''. It spans the period of time ...
Era 3600 Mya. The
beginnings
Beginnings may refer to:
Literature
* ''Beginnings'' (collection), a 1988 collection of short stories and poems by Gordon R. Dickson
* ''Beginnings'' (Honorverse), a 2013 collection of short stories in the Worlds of Honor series
* ''Beginnings ...
of
life on Earth Life on Earth may refer to:
Science
* Life
* Earliest known life forms
* Evolutionary history of life
** Abiogenesis
Film and television
* ''Life on Earth'' (film) (''La Vie Sur Terre''), a 1998 Malian film
* ''Life on Earth'' (TV series), a 197 ...
have been dated to this era and evidence of
cyanobacteria
Cyanobacteria (), also known as Cyanophyta, are a phylum of gram-negative bacteria that obtain energy via photosynthesis. The name ''cyanobacteria'' refers to their color (), which similarly forms the basis of cyanobacteria's common name, blu ...
date to 3500 Mya, comparatively shortly after the Eoarchean. At that time, the
atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A s ...
was without oxygen and the pressure values ranged from 10 to 100
bar
Bar or BAR may refer to:
Food and drink
* Bar (establishment), selling alcoholic beverages
* Candy bar
* Chocolate bar
Science and technology
* Bar (river morphology), a deposit of sediment
* Bar (tropical cyclone), a layer of cloud
* Bar (u ...
(around 10 to 100 times the atmospheric pressure today).
Chronology
The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of the ''Early Archean'' Eon (which is now an obsolete name) alongside the
Paleoarchean
The Paleoarchean (), also spelled Palaeoarchaean (formerly known as early Archean), is a Geologic time scale#Terminology, geologic era within the Archean, Archaean Eon. The name derives from Greek "Palaios" ''ancient''. It spans the period of time ...
Era.
The
International Commission on Stratigraphy
The International Commission on Stratigraphy (ICS), sometimes referred to unofficially as the "International Stratigraphic Commission", is a daughter or major subcommittee grade scientific daughter organization that concerns itself with stratigra ...
now officially recognizes the Eoarchean Era as the
first part of the
Archaean Eon
Eon or Eons may refer to: Time
* Aeon, an indefinite long period of time
* Eon (geology), a division of the geologic time scale
Arts and entertainment
Fictional characters
* Eon, in the 2007 film '' Ben 10: Race Against Time''
* Eon, in the ...
, preceded by the
Hadean Eon, during which the Earth is believed to have been essentially molten.
The Eoarchaean's lower boundary or starting point of 4
Gya
A billion years or giga-annum (109 years) is a unit of time on the petasecond scale, more precisely equal to seconds (or simply 1,000,000,000 years).
It is sometimes abbreviated Gy, Ga ("giga-annum"), Byr and variants. The abbreviations Gya or ...
(4
billion years ago
bya or b.y.a. is an abbreviation for "billion years ago". It is commonly used as a unit of time to denote length of time before the present in 109 years. This initialism is often used in the sciences of astronomy, geology, and paleontology.
The " ...
) is officially recognized by the International Commission on Stratigraphy.
The name comes from two
Greek
Greek may refer to:
Greece
Anything of, from, or related to Greece, a country in Southern Europe:
*Greeks, an ethnic group.
*Greek language, a branch of the Indo-European language family.
**Proto-Greek language, the assumed last common ancestor ...
words: ' (dawn) and ' (ancient). The first supercontinent candidate
Vaalbara
Vaalbara was an Archean supercontinent consisting of the Kaapvaal Craton (now in eastern South Africa) and the Pilbara Craton (now in north-western Western Australia). E. S. Cheney derived the name from the last four letters of each craton's name ...
appeared around the end of this period at about .
Geology
The beginning of the Eoarchean is characterized by heavy
asteroid bombardment within the
Inner Solar System
The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
: the
Late Heavy Bombardment
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypoth ...
. The largest Eoarchean rock formation is the
Isua Greenstone Belt on the south-west coast of Greenland, which dates from 3.8 billion years. The
Acasta Gneiss within the
Canadian Shield have been dated to be 4,031 Ma and are therefore the oldest preserved rock formations. In 2008, another rock formation was discovered in the
Nuvvuagittuq Greenstone Belt
The Nuvvuagittuq Greenstone Belt (NGB; Inuktitut: ) is a sequence of metamorphosed mafic to ultramafic Volcanic rock, volcanic and associated sedimentary rocks (a greenstone belt) located on the eastern shore of Hudson Bay, 40 km southeast of ...
in northern
Québec, Canada
Quebec ( ; )According to the Government of Canada, Canadian government, ''Québec'' (with the acute accent) is the official name in Canadian French and ''Quebec'' (without the accent) is the province's official name in Canadian English is ...
which has been dated to be . These formations are presently under intense investigation.
Atmosphere
3,850 million years old Greenland
apatite
Apatite is a group of phosphate minerals, usually hydroxyapatite, fluorapatite and chlorapatite, with high concentrations of OH−, F− and Cl− ions, respectively, in the crystal. The formula of the admixture of the three most common e ...
shows evidence of
Carbon-12 enrichment. This has sparked a debate whether there might have been photosynthetic life before 3.8 billion years.
Proposed subdivisions
*Eoarchean Era — 4031–3600 Mya
**Acastan Period — 4031–3810 Mya
**Isuan Period — 3810–3600 Mya
See also
*
Precambrian Supereon (4600-539 Mya)
**
Hadean Eon (4600-4000 Mya)
**
Archean
The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth
Earth ...
Eon (4000-2500 Mya)
***
Paleoarchean
The Paleoarchean (), also spelled Palaeoarchaean (formerly known as early Archean), is a Geologic time scale#Terminology, geologic era within the Archean, Archaean Eon. The name derives from Greek "Palaios" ''ancient''. It spans the period of time ...
Era (3600-3200 Mya)
***
Mesoarchean
The Mesoarchean (, also spelled Mesoarchaean) is a geologic era in the Archean Eon, spanning , which contains the first evidence of modern-style plate subduction and expansion of microbial life. The era is defined chronometrically and is not r ...
Era (3200-2800 Mya)
***
Neoarchean
The Neoarchean (; also spelled Neoarchaean) is the last geologic era in the Archean eon that spans from 2800 to 2500 million years ago—the period being defined chronometrically and not referencing a specific level in a rock section on Ear ...
Era (2800-2500 Mya)
**
Proterozoic Eon (2500-539 Mya)
References
Further reading
*
External links
*
Taxonconcept.stratigraphy.ne: A short fact sheet on the Eoarchean
{{Geological history, c
*01
Geological eras
Precambrian geochronology