Eoarchaean (3.8 b.y.) Greenlandite specimen (fuchsite-quartz gneiss),Nuup Kangerlua, Greenland.Garnetparagneiss, Nuvvuagittuq Greenstone Belt, Canada. 4.28 Ga old: the oldest known Earth rock of which direct samples are available.
The Eoarchean Era was formerly officially unnamed and informally referred to as the first part of theEarly Archean Eon (which is now an obsolete name) alongside thePaleoarchean Era.
The Eoarchaean's lower boundary or starting point of 4.031Gya (4031million years ago) is officially recognized by the International Commission on Stratigraphy.[6]
The name comes from twoGreek words:eos (dawn) andArchaios (ancient). The firstsupercontinent candidateVaalbara appeared around the end of this period at about3,600 million years ago.
The beginning of the Eoarchean is characterized by heavyasteroid bombardment within theInner Solar System: theLate Heavy Bombardment. The largest Eoarchean rock formation is theIsua Greenstone Belt on the south-west coast ofGreenland, which dates from 3.8 billion years. TheAcasta Gneiss within theCanadian 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 theNuvvuagittuq Greenstone Belt in northernQuébec, Canada, which has been dated to be4,280 million years ago.[7] These formations are presently under intense investigation.[clarification needed][8] Oxygen isotope ratios show that thehydrological cycle had begun by the early Eoarchaean and possibly earlier.[9] Carbonate precipitation (caused by heating of seawater by hydrothermal vents) acted as an important sink regulating the concentration ofcarbon dioxide in the atmosphere during this era.[10]
3,850 million years oldapatite from Greenland shows evidence ofCarbon-12 enrichment. This has sparked a debate whether there might have been photosynthetic life before 3.8 billion years ago.[11][needs update?]
^Mulkidjanian, A. Y. (2011). "Energetics of the First Life". In Egel, R.; Lankenau, D.-H.; Mulkidjanian, A. Y. (eds.).Origins of Life: The Primal Self-Organization. Heidelberg: Springer Verlag. pp. 3–33.ISBN978-3-642-21625-1.
^David, J.; Godin, L.; Stevenson, R. K.; O'Neil, J.; Francis, D. (2009). "U-Pb ages (3.8–2.7 Ga) and Nd isotope data from the newly identified Eoarchean Nuvvuagittuq supracrustal belt, Superior Craton, Canada".Geological Society of America Bulletin.121 (1–2):150–163.doi:10.1130/B26369.1.
^Van Kranendonk, Martin J. (2012). "16: A Chronostratigraphic Division of the Precambrian: Possibilities and Challenges". In Gradstein, Felix M.; Ogg, James G.; Schmitz, Mark D.; Ogg, Gabi M. (eds.).The geologic time scale 2012 (1st ed.). Amsterdam: Elsevier. pp. 359–365.ISBN978-0-44-459425-9.
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