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Akilia Island is an island in southwestern Greenland, about 22 kilometers south of Nuuk (Godthåb), at . Akilia is the location of a rock formation that has been proposed to contain the oldest known sedimentary rocks on Earth,〔 McGregor, VR, Mason, B (1977 ''Petrogenesis and geochemistry of metabasaltic and metasedimentary enclaves in the Amîtsoq gneisses, West Greenland''. American Mineralogist, v. 62, p. 887-904〕〔Nutman AP, Mojzsis, SJ, Friend, CRL (1997) ''Recognition of ≥3850 Ma water-lain sediments in West Greenland and their significance for the early Archaean Earth''. Geochimica et Cosmochimica Acta, v. 61, p. 2475-2484. 〕 and perhaps the oldest evidence of life on Earth.〔Mojzsis, SJ, Arrhenius, G, McKeegan, KD, Harrison, TM, Nutman, AP, Friend, CRL (1996) ''Evidence for life on Earth before 3,800 million years ago''. Nature, v. 384, p. 55-59〕 ==Geology== The rocks in question are part of a metamorphosed supracrustal sequence located at the south-western tip of the island. The sequence has been dated as no younger than 3.85 billion years old - that is, in the Hadean eon - based on the age of an igneous band that cuts the rock.〔Manning, CE, Mojzsis, SJ, Harrison, TM (2006) ''Geology, age and origin of supracrustal rocks at Akilia, West Greenland''. American Journal of Science, v. 206, p. 303-366〕 The supracrustal sequence contains layers rich in iron and silica, which are variously interpreted as banded iron formation, chemical sediments from submarine hot springs, or hydrothermal vein deposits. Carbon in the rock, present as graphite, shows low levels of carbon-13,〔 which may suggest an origin as isotopically light organic matter derived from living organisms.〔Schidlowski, M (1988) ''A 3,850-Million-Year Isotopic Record of Life From Carbon in Sedimentary-Rocks''. Nature, v. 333, p. 313-318〕 However, this interpretation is complicated because of high-grade metamorphism that affected the Akilia rocks after their formation. The sedimentary origin, age and the carbon content of the rocks have been questioned.〔Myers, JS, Crowley, JL (2000) ''Vestiges of life in the oldest Greenland rocks? A review of early Archean geology in the Godthåbsfjord region, and reappraisal of field evidence for >3850 Ma life on Akilia''. Precambrian Research, v. 103, p. 101-124.〕〔 Fedo, CM, Whitehouse, MJ (2002) ''Metasomatic origin of quartz-pyroxene rock, Akilia, Greenland, and implications for Earth's earliest life''. Science, v. 296, p. 1448-1452〕〔Lepland, A, van Zuilen, M, Arrhenius, G, Whitehouse, M, Fedo, C (2005) ''Questioning the evidence for Earth's earliest life—Akilia revisited''. Geology, v. 33, p. 77-79〕 If the Akilia rocks do show evidence of life by 3.85 Ga, it would challenge models which suggest that Earth would not be hospitable to life at this time. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Akilia」の詳細全文を読む スポンサード リンク
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