Hadean
| Hadean | ||||||
|---|---|---|---|---|---|---|
| Chronology | ||||||
| ||||||
| Etymology | ||||||
| Synonym(s) | Priscoan Period Eon | |||||
| Stratigraphic unit | Eonothem | |||||
| First proposed by | Preston Cloud, 1972 | |||||
| Time span formality | Formal | |||||
| Lower boundary definition | (4567.30 ± 0.16) Ma[1] | |||||
| Lower GSSA ratified | October 5th, 2022[1] | |||||
| Upper boundary definition | Ten oldest U-Pb zircon ages | |||||
| Upper boundary GSSA | Along the Acasta River, Northwest Territories, Canada 65°10′26″N 115°33′14″W / 65.1738°N 115.5538°W | |||||
| Upper GSSA ratified | 2023[2] | |||||
The Hadean (
Hadean rocks are very rare, largely consisting of
Etymology
The eon's name "Hadean" comes from
The term was coined by American geologist Preston Cloud, originally to label the period before the earliest-known rocks on Earth.[7][8] W.B. Harland later coined an almost synonymous term, the Priscoan period, from priscus, the Latin word for 'ancient'.[9] Other, older texts refer to the eon as the Pre-Archean.[10][11]
Rock dating
In the last decades of the 20th century, geologists identified a few Hadean rocks from western Greenland, northwestern Canada, and Western Australia. In 2015, traces of carbon minerals interpreted as "remains of biotic life" were found in 4.1-billion-year-old rocks in Western Australia.[12][13]
The oldest dated
In many other areas,
Atmosphere
A sizable quantity of water would have been in the material that formed Earth.[16] Water molecules would have escaped Earth's gravity more easily when the planet was less massive during its formation. Photodissociation by short-wave ultraviolet in sunlight could split surface water molecules into oxygen and hydrogen, the former of which would be readily removed by the then-reducing atmosphere, while the latter (along with the similarly light helium) would be expected to continually leave the atmosphere (even to the present day) due to atmospheric escape.
Part of the ancient planet is theorized to have been disrupted by the
2 atmosphere with hydrogen and water vapor. The initial heavy atmosphere had a surface temperature of 230 °C (446 °F) and an atmospheric pressure of above 27 standard atmospheres.[18]
Oceans
Studies of zircons have found that liquid water may have existed between 4.0 and 4.4 billion years ago, very soon after the formation of Earth.[14][20] Liquid water oceans existed despite the high surface temperature, because at an atmospheric pressure of 27 atmospheres, water remains liquid even at those high temperatures.[18]
The most likely source of the water in the Hadean ocean was outgassing from the Earth's mantle.[21] Bombardment origin of a substantial amount of water is unlikely, due to the incompatibility of isotope fractions between the Earth and comets.[16]
Asteroid impacts during the Hadean and into the Archean would have periodically disrupted the ocean. The geological record from 3.2 Gya contains evidence of multiple impacts of objects up to 100 kilometres (62 mi) in diameter.[22] Each such impact would have boiled off up to 100 metres (330 ft) of a global ocean, and temporarily raised the atmospheric temperature to 500 °C (932 °F).[22] However, the frequency of meteorite impacts is still under study: the Earth may have gone through long periods when liquid oceans and life were possible.[20]
The liquid water would absorb the carbon dioxide in the early atmosphere, not enough by itself to substantially reduce the amount of CO
2.[18]
Plate tectonics
A 2008 study of zircons found that Australian Hadean rock contains minerals pointing to the existence of plate tectonics as early as 4 billion years ago (approximately 600 million years after Earth's formation).[23] However, some geologists suggest that the zircons could have been formed by meteorite impacts.[24] The direct evidence of Hadean geology from zircons is limited, because the zircons are largely gathered in one locality in Australia.[6][25] Geophysical models are underconstrained, but can paint a general picture of the state of Earth in the Hadean.[6][26]
Subduction due to plate tectonics would have removed carbonate from the early oceans, contributing to the removal of the CO
2-rich early atmosphere. Removal of this early atmosphere is evidence of Hadean plate tectonics.[31]
If plate tectonics occurred in the Hadean, it would have formed
Continents
The amount of exposed land in the Hadean is only loosely dependent on the amount of continental crust: it also depends on the ocean level.
Possible life
Abundant Hadean-like
See also
- Chaotian (geology) – Proposed era of the Hadean eon
- Faint young Sun paradox – Paradox concerning water on early Earth
- Formation and evolution of the Solar System
- Hadean zircon – Oldest-surviving crustal material from the Earth's earliest geological time period
- History of Earth – Development of planet Earth from its formation to the present day – the first sections describe the formation of Earth
- Oldest dated rocks – Includes rocks over 4 billion years old from the Hadean Eon
- Precambrian – History of Earth 4600–539 million years ago
- Timeline of natural history
References
- ^ a b c Cohen, Kim (October 2022). "New edition of the Chart - 2022-10". International Commission on Stratigraphy. Retrieved 16 January 2023.
2022/10 - Hadean: GSSA instated as ratified by IUGS (5-10-2022). The GSSA is 4,567.30 ± 0.16 Ma.
- ^ "Global Boundary Stratotype Section and Point". International Commission of Stratigraphy. Retrieved 29 October 2023.
- S2CID 130092094. Retrieved 2022-10-02.
- ^ "Age of the Earth". U.S. Geological Survey. 1997. Archived from the original on 23 December 2005. Retrieved 2022-10-03.
- S2CID 229513433.
- ^ PMID 34833018.
- .
- ISBN 9780521786737.
- ^ "Priscoan". Oxford Living dictionaries. Archived from the original on 2018-11-29.
- ISBN 0-471-01488-5.
- .
- ^ Borenstein, Seth (19 October 2015). "Hints of life on what was thought to be desolate early Earth". Excite. Yonkers, NY: Mindspark Interactive Network. Associated Press. Retrieved 2015-10-20.
- PMID 26483481.
- ^ S2CID 4319774.
- .
- ^ .
- ^ Taylor, G. Jeffrey. "Origin of the Earth and Moon". Solar System Exploration. NASA. Archived from the original on March 8, 2015.
- ^ PMID 11259665.
- .
- ^ PMID 16196254. Archived from the originalon 2013-06-16. Retrieved 2006-08-22.
- ISBN 9780081029091.
- ^ doi:10.1130/G36665.1.
- ^ Chang, Kenneth (December 2, 2008). "A New Picture of the Early Earth". The New York Times.
- ^ Kenny, GG; Whitehouse, MJ; Kamber, BS; et al. (April 12, 2016). "Differentiated impact melt sheets may be a potential source of Hadean detrital zircon". Retrieved March 6, 2017.
- ^ S2CID 128932829.
- S2CID 2958757.
- S2CID 233441822.
- S2CID 206643793.
- S2CID 228993361.
- S2CID 43547982.
- S2CID 6902632.
- ^ PMID 32671213.
- .
- S2CID 206538532.
- S2CID 13666395.
- PMID 34068713.
- S2CID 232206926.
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- doi:10.1130/G25031A.1;.)
{{cite journal}}: CS1 maint: ignored DOI errors (link - PMID 30400350.
- ^ PMID 36932102.
- PMID 27012512.
Further reading
- Hopkins, Michelle; Harrison, T. Mark; Manning, Craig E. (2008). "Low heat flow inferred from >4 Gyr zircons suggests Hadean plate boundary interactions". S2CID 4417456.
- Wyche, S.; Nelson, D. R.; Riganti, A. (2004). "4350–3130 Ma detrital zircons in the Southern Cross Granite–Greenstone Terrane, Western Australia: implications for the early evolution of the Yilgarn Craton". Australian Journal of Earth Sciences. 51 (1): 31–45. .
- Carley, Tamara L.; et al. (2014). "Iceland is not a magmatic analog for the Hadean: Evidence from the zircon record". Earth and Planetary Science Letters. 405 (1): 85–97. .
- Marchi, S.; et al. (2014). "Widespread mixing and burial of Earth's Hadean crust by asteroid impacts". Nature. 511 (7511): 578–582. S2CID 205239647.
External links
