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Earth's atmosphere at this stage was somewhat comparable to today's atmosphere of Titan. [19] The Archean atmosphere is thought to have almost completely lacked free oxygen; oxygen levels were less than 0.001% of their present atmospheric level, [20] [21] with some analyses suggesting they were as low as 0.00001% of modern levels. [22]
It has long been hypothesized that life may have existed on Mars due to the similarity of environmental and tectonic conditions during the Archean time. [2] By knowing the environments in which early life evolved on Earth, and the rock types that preserve them, scientists can have a better understanding of where to look for life on Mars.
The first eon in Earth's history, the Hadean, begins with the Earth's formation and is followed by the Archean eon at 3.8 Ga. [2]: 145 The oldest rocks found on Earth date to about 4.0 Ga, and the oldest detrital zircon crystals in rocks to about 4.4 Ga, [34] [35] [36] soon after the formation of the Earth's crust and the Earth
The Neoarchean (/ ˌ n iː oʊ. ɑːr ˈ k iː ə n / NEE-oh-ar-KEE-ən; 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 Earth.
The Precambrian is an informal unit of geologic time, [3] subdivided into three eons (Hadean, Archean, Proterozoic) of the geologic time scale. It spans from the formation of Earth about 4.6 billion years ago to the beginning of the Cambrian Period, about 538.8 million years ago , when hard-shelled creatures first appeared in abundance.
ɑːr ˈ k iː ə n / EE-oh-ar-KEE-ən; also spelled Eoarchaean) is the first era of the Archean Eon of the geologic record. It spans 431 million years, from the end of the Hadean Eon 4031 Mya to the start of the Paleoarchean Era 3600 Mya. Some estimates place the beginnings of life on Earth in this era, while others [2] place it earlier.
The Mesoarchean (/ ˌ m iː z oʊ. ɑːr ˈ k iː ə n, ˌ m ɛ z oʊ-/ MEE-zoh-ar-KEE-ən, MEZ-oh-, 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 Isua Greenstone Belt is an Archean greenstone belt in southwestern Greenland, aged between 3.7 and 3.8 billion years. [2] The belt contains variably metamorphosed mafic volcanic and sedimentary rocks, and is the largest exposure of Eoarchaean supracrustal rocks on Earth. [3]