page_title: Eoarchean
hierarchical_section_title: Eoarchean
caption_attribution_description: Greenlandite (fuchsite-quartz gneiss) (2.7 cm across at its widest) from the Precambrian of southwestern Greenland. Green = fuchsite; gray = quartz; a few small, scattered pyrite crystals (brassy gold-colored) are also visible. Attractive greenish-colored gneisses in southwestern Greenland that contain the minerals fuchsite (green) and quartz (gray) have been informally called greenlandite. Fuchsite is a chromian muscovite mica (K(Al,Cr)2AlSi3O10(OH,F)2 - potassium chromium hydroxy-fluoro-aluminosilicate); it is typically encountered in schistose rocks. Greenland greenlandite is part of a 3.8 billion year old, highly metamorphosed succession of rocks. These represent the oldest known supracrustal rocks on Earth (the oldest crustal Earth rocks include 4.03 billion year old Acasta Gneiss, 4.28 b.y. rocks from the eastern Hudson Bay area, and 4.45-4.55 b.y. rocks in the subsurface of Baffin Island, Canada). Locality: undisclosed locality in the Godthåbsfjord area or Nuuk area, southwestern Greenland. Age: Eoarchean boundary, 3.8 billion years.
context_page_description: The Eoarchean is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4 billion years ago to the start of the Paleoarchean Era 3600 Mya. The beginnings of life on Earth have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside this era. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar.
context_section_description: The Eoarchean ( /ˌiːoʊ.ɑːrˈkiːən/; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record for which the Earth has a solid crust. It spans 400 million years from the end of the Hadean Eon 4 billion years ago (4000 Mya) to the start of the Paleoarchean Era 3600 Mya.  The beginnings of life on Earth have been dated to this era and evidence of cyanobacteria date to 3500 Mya, just outside this era. At that time, the atmosphere was without oxygen and the pressure values ranged from 10 to 100 bar (around 10 to 100 present-time atmospheres).
caption: Eoarchaean (3.8 b.y.) Greenlandite  specimen (fuchsite-quartz gneiss), Nuup Kangerlua, Greenland.
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