Origin of water on Earth

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Water covers about 75% of the Earth's surface

The origin of water on Earth, or the reason that there is clearly more liquid water on the Earth than on the other rocky planets of the Solar System, is not completely understood. There exist numerous more or less mutually compatible hypotheses as to how water may have accumulated on the Earth's surface over the past 4.6 billion years in sufficient quantity to form oceans.

Possible reasons[edit]

Planetary cooling[edit]


Extraplanetary sources[edit]


Planetesimals heated by the decay of aluminium. This could cause water to rise to the surface.[2] Recent studies suggest that water with similar deuterium-to-hydrogen ratio was already available at the time of the Earth's formation, as evidenced in ancient "eucrites" meteorites originating from the asteroid Vesta.[3]

That the Earth's water originated purely from comets is implausible, as a result of measurements of the isotope ratios of hydrogen in the four comets Halley, Hyakutake, Hale-Bopp, and 67P/Churyumov–Gerasimenko by researchers such as David Jewitt, as according to this research the ratio of deuterium to protium (D/H ratio) of the comets is approximately double that of oceanic water. What is however unclear is whether these comets are representative of those from the Kuiper Belt. According to Alessandro Morbidelli [4] the largest part of today's water comes from protoplanets formed in the outer asteroid belt that plunged towards the Earth, as indicated by the D/H proportions in carbon-rich chondrites. The water in carbon-rich chondrites point to a similar D/H ratio as oceanic water. Nevertheless, mechanisms have been proposed[5] to suggest that the D/H-ratio of oceanic water may have increased significantly throughout Earth's history. Such a proposal is consistent with the possibility that a significant amount of the water on Earth was already present during the planet's early evolution.


Hydrate minerals[edit]

Gradual leakage of water stored in hydrate minerals of the Earth's rocks.[citation needed]

Volcanic activity[edit]

Water may also have come from volcanism: water vapor originating in volcanic eruptions condensing and forming rain.[8]

Water in the development of the Earth[edit]

A sizeable quantity of water would have been in the material which formed the Earth.[9][10] Water molecules would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen and helium are expected to leak from the atmosphere continually, but the lack of denser noble gases in the modern atmosphere suggests that something disastrous happened to the early atmosphere.


Study of zircons has found that liquid water must have existed as long ago as 4.4 Ga, very soon after the formation of the Earth.[13][14][15] This requires the presence of an atmosphere. The Cool Early Earth theory covers a range from about 4.4 Ga to 4.0 Ga.

In fact, recent studies of zircons (in the fall of 2008) found in Australian Hadean rock hold minerals that point to the existence of plate tectonics as early as 4 billion years ago. If this holds true, the previous beliefs about the Hadean period are far from correct. That is, rather than a hot, molten surface and atmosphere full of carbon dioxide, the Earth's surface would be very much like it is today. The action of plate tectonics traps vast amounts of carbon dioxide, thereby eliminating the greenhouse effects and leading to a much cooler surface temperature and the formation of solid rock, and possibly even life.[16]

Role of organisms[edit]

Some terrestrial water may have had a bio-chemical origin, during the Great Oxygenation Event, via redox reactions and photosynthesis.[17]

In the early 1930s, Cornelis Van Niel discovered that sulfide-dependent chemoautotrophic bacteria (purple sulfur bacteria) fix carbon and synthesize water as a byproduct of a photosynthetic pathway using hydrogen sulfide and carbon dioxide:[18]

CO2 + 2H2S → CH2O + H2O + 2S

Few organisms utilize this method of photosynthesis today, making their water contribution negligible. But on the hydrogen sulfide-rich and oxygen-poor early planet, a small but significant portion of the earth's water may have been synthesized biochemically through this pathway.[citation needed]

See also[edit]


  • Jörn Müller, Harald Lesch (2003): Woher kommt das Wasser der Erde? - Urgaswolke oder Meteoriten. Chemie in unserer Zeit 37(4), pg. 242 – 246, ISSN 0009-2851
  • Parts of this article were translated from the original article from the German Wikipedia, on 4/3/06


  1. ^ http://www.sciencemag.org/content/347/6220/1261952
  2. ^ http://phys.org/news/2014-02-earth.html#jCp
  3. ^ http://www.sciencemag.org/content/346/6209/623
  4. ^ Alessandro Morbidelli et al. Meteoritics & Planetary Science 35, 2000, S. 1309–1329
  5. ^ H. Genda, M. Ikoma, Origin of the Ocean on the Earth: Early Evolution of Water D/H in a Hydrogen-rich Atmosphere. Accessible at http://arxiv.org/abs/0709.2025
  6. ^ Cowen, Ron (9 May 2013). "Common source for Earth and Moon water". Nature. doi:10.1038/nature.2013.12963. 
  7. ^ "Herschel discovers water vapour around dwarf planet Ceres". European Space Agency. Retrieved 10 February 2014. 
  8. ^ http://live.huffingtonpost.com/r/highlight/scientists-discover-where-earths-water-originated/564ba93d99ec6d09c3000126?source=gravityRR&cps=gravity_5060_-7528146454370360511
  9. ^ Drake, Michael J. (April 2005). "Origin of water in the terrestrial planets". Meteoritics & Planetary Science (John Wiley & Sons) 40 (4): 519–527. Bibcode:2005M&PS...40..519D. doi:10.1111/j.1945-5100.2005.tb00960.x. 
  10. ^ Drake, Michael J.; et al. (August 2005). "Origin of water in the terrestrial planets". Asteroids, Comets, and Meteors (IAU S229). 229th Symposium of the International Astronomical Union 1 (4). Búzios, Rio de Janeiro, Brazil: Cambridge University Press. pp. 381–394. Bibcode:2006IAUS..229..381D. doi:10.1017/S1743921305006861. ISBN 978-0521852005. 
  11. ^ "Solar System Exploration: Science & Technology: Science Features: View Feature". Solarsystem.nasa.gov. 2004-04-26. Retrieved 2009-08-20. 
  12. ^ N. H. Sleep; K. Zahnle & P. S. Neuhoff. "Inaugural Article: Initiation of clement surface conditions on the earliest Earth - Sleep et al. 98 (7): 3666 - Proceedings of the National Academy of Sciences". Pnas.org. Retrieved 2009-08-20. 
  13. ^ "ANU - Research School of Earth Sciences - ANU College of Science - Harrison". Ses.anu.edu.au. Retrieved 2009-08-20. 
  14. ^ "ANU - OVC - MEDIA - MEDIA RELEASES - 2005 - NOVEMBER - 181105HARRISONCONTINENTS". Info.anu.edu.au. Retrieved 2009-08-20. 
  15. ^ "A Cool Early Earth". Geology.wisc.edu. Retrieved 2009-08-20. 
  16. ^ Chang, Kenneth (2008-12-02). "A New Picture of the Early Earth". The New York Times. Retrieved 2010-05-20. 
  17. ^ "The oxygenation of the atmosphere and oceans" (PDF), Philosophical Transactions of The Royal Society: Biological Sciences, 29 June 2006 
  18. ^ van Niel, C.B. (1931). "Photosynthesis of bacteria". Arch. Mikrobiol. 3 (1). 

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