from Wikipedia, the free encyclopedia
Aeonothem Arathem system Age
( mya )
later later later


Duration: 300 Ma

Duration: 400 Ma

Duration: 400 Ma

Duration: 400 Ma

formerly: Hadaikum

The Eoarchean is a geological age ( era ) in the aeon of the Archean . It represents the earliest of four eras within the Archaic, the second eon of earth's history. The Eoarchaic (from ancient Greek Ἠώς, Ēōs for 'dawn') follows the first eon of earth's history, the Hadaic , in about 4000 million years BP which the planet earth was formed . The Eoarchean ends around 3600 million years BP with the transition to the Paleoarchean .

Redefinition of the Precambrian

In the course of the redefinition of the Precambrian , the Eoarchean is to be dropped, and the Paleoarchean will take its place. Its beginning, which is defined by the Acasta gneiss , the oldest known rock in the history of the earth, is to be brought forward by 30 million years to 4030 million years BP. The end of the Paleoarchean is then set at 3490 million years BP by a GSSP at the base of the Dresser Formation , which marks the first appearance of stromatolites . The paleoarchean contains two periods , the 4030-3810 million a BP lasting Acastum and the 3810-3490 million a BP lasting Isuum . The boundary between the Acastum and the Isuum is chronometrically defined by the appearance of the first supracrustal rocks of the Isua greenstone belt .


It is characteristic of the Eoarchean that the earth has a solid crust for the first time in this age , which, however, still constantly breaks in many places and is permeated by glowing lava flows. At the beginning of the Eoarchic there is a period of very severe asteroid impacts in the inner solar system , the Late Heavy Bombardment .

The Eoarchean is the earliest phase of our planet from which rock formations have been preserved. The largest is the Isua gneiss on the southwest coast of Greenland, around 3800 million years old. Since the discovery of the Acasta gneiss in 1989 in the northwestern Canadian shield , which were later dated to 4030 million years BP , these have been considered to be the oldest preserved rocks. In 2008, however, rocks were discovered in the Nuvvuagittuq greenstone belt in northern Québec , Canada , which were dated to approximately 4280 mya. They are still the subject of current research.

It is now considered certain that oceans already existed in the Eoarchean. The earth's atmosphere of the era was completely different from ours today and was presumably a reducing one .


An outstanding development of the eoarchic is the formation of the earliest forms or pre-forms of organic life in the form of prokaryotes (simple single cells without a nucleus). Certain carbon isotopes found in the oldest known rock formations from Greenland (see above) have been assigned an organic origin. The earliest stromatolites were also created in the Eoarchean - or possibly only in the following age, the Paleoarchean.


  • Mary Fowler, Cindy Ebinger, Chris Hawkesworth (Eds.): The Early Earth: Physical, Chemical and Biological Development (=  Geological Society Special Publication . No. 199 ). The Geological Society, London 2002, ISBN 1-86239-109-2 (English, limited preview in Google Book Search).

Web links

  • Douglas Page: The Isua Rocks. 2000 (English).;

Individual evidence

  1. ^ Felix M. Gradstein et al .: On the Geologic Time Scale . In: Newsletters on Stratigraphy . tape 45 , no. 2 , April 2012, p. 171–188 , doi : 10.1127 / 0078-0421 / 2012/0020 (English, freely available online through researchgate.net ).
  2. Jonathan O'Neil, Richard W. Carlson, Don Francis, Ross K. Stevenson: Neodymium-142 Evidence for Hadean Mafic Crust . In: Science . tape 321 , no. 5897 , September 26, 2008, p. 1828–1831 , doi : 10.1126 / science.1161925 (English, freely available online through researchgate.net ).
  3. Jean David, Laurent Godin, Ross Stevenson, Jonathan O'Neil, Don Francis: U-Pb ages (3.8-2.7 Ga) and Nd isotope data from the newly identified Eoarchean Nuvvuagittuq supracrustal belt, Superior Craton, Canada . In: Geological Society of America Bulletin . tape 121 , no. 1-2 , January 2009, ISSN  0016-7606 , p. 150–163 , doi : 10.1130 / B26369.1 (English, freely available online through researchgate.net ).
  4. Tsuyoshi Iizuka, Tsuyoshi Komiya, Yuichiro Ueno, Ikuo Katayama, Yosuke Uehara, Shigenori Maruyama, Takafumi Hirata, Simon P. Johnson, Daniel J. Dunkley: Geology and zircon geochronology of the Acasta Gneiss Complex, northwestern Canada: New constraints on its tectonotherern history . In: Precambrian Research . tape 153 , no. 3–4 , March 1, 2007, pp. 179–208 , doi : 10.1016 / j.precamres.2006.11.017 (English, freely available online through researchgate.net ).