4700–4600 million years ago
The Chaotian is an unofficial eon or era on the Geologic time scale, first proposed in 2010. This proposed geological time period starts with the creation of Earth about 4.6 billion years ago (Gya) / 4600 million years ago (Mya) to the beginning of the Zirconian era 4,404 Mya. It is named after Chaos, the primeval void, in Greek mythology.
It is alternately set to be the earliest era within the Hadean eon, or its own eon preceding the Hadean. When first proposed, it was conceived of as a pre-Hadean eon which ended with a hypothetical collision of the proto-Earth, leading to the formation of the Moon. Later scholarship defined it as the first era of the Hadean eon. As of 2012[update], it is being considered as a proposed revision of the Precambrian time scale.
This geological era designation was proposed by scientists at the Ames Research Center in 2010 to formalize terminology in the earliest stages of Earth's history. This proposal divides the Chaotian into the Eochaotian (4.7–4.65 Gya) and Neochaotian (4,650–4,600 Mya) eras. The Eochaotian is proposed to be divided into the Nephelean (4.7–4.68 Gya) and Erebrean (4,680–4,650 Mya) periods, and the Neochaotian into the Hyperitian (4,650–4,620 Mya) and Titanomachean (4,620–4,600 Mya). As of May 2017[update], this has been adopted by the IUGS.
Age of the EarthEdit
However, the exact age of our solar system—and thus the age of the Earth—is still an ongoing question. Outgassing and differentiation of the earth in an iron-rich core and mantle may have been completed 4,450 Mya. The giant impact hypothesis' proposed collision with Theia, leading to the formation of the Moon, is estimated to have occurred 4,527 Mya. Calcium-aluminium-rich inclusions (CAI), the first condensate from the planetary orbit, were dated to 4,567.30 Mya (± 0.16 Mya) by the uranium-lead method. In 1979, dating of the Mundrabilla iron meteorite of Western Australia using the argon method determined an age of 4,570 Mya (± 60 Mya). Manganese-chromium dating of chondrules revealed an age of 4,571 Mya.
Due to the uncertainty of the lower limit of Earth's age, 4,600 Mya is used as the estimated lowest limit of geological time.
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