Origin of water on Earth
From Wikipedia, the free encyclopedia
The origin of water on Earth, or the reason that there is clearly
more water on the Earth than on the other planets of the Solar System
, has not been clarified. There are several acknowledged theories as to
how the world's oceans were formed over the past 4.6 billion years.
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[edit]Origins
Some of the most likely contributory factors to the origin of the Earth's oceans are as follows:
- The cooling down of the primordial world to the point where the outgassed volatile components
- were held in an atmosphere of sufficient pressure for the stabilization and retention of liquid water.
- Comets, trans-Neptunian objects or water-rich meteorites (protoplanets) from the outer reaches
- of the main asteroid belt colliding with the Earth may have brought water to the world's oceans
- . Measurements of the ratio of the hydrogen isotopes deuterium and protium point to asteroids,
- since similar percentage impurities in carbon-rich chondrites were found in oceanic water,
- whereas previous measurement of the isotopes' concentrations in comets and trans-Neptunian
- objects correspond only slightly to water on the Earth.
- Biochemically through mineralization and photosynthesis.[citation needed]
- Gradual leakage of water stored in hydrous minerals of the Earth's rocks.
- Photolysis: radiation can break down chemical bonds on the surface.
[edit]Water in the development of the Earth
See also: Planetary differentiation
A sizeable quantity of water would have been in the material which formed the Earth.[1][2] Water molecules
would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen
and helium are expected to continually leak from the atmosphere, but the lack of denser noble gases in the
modern atmosphere suggests that something disastrous happened to the early atmosphere.
would have escaped Earth's gravity more easily when it was less massive during its formation. Hydrogen
and helium are expected to continually leak from the atmosphere, but the lack of denser noble gases in the
modern atmosphere suggests that something disastrous happened to the early atmosphere.
Part of the young planet is theorized to have been disrupted by the impact which created the Moon, which
should have caused melting of one or two large areas. Present composition does not match complete
melting and it is hard to completely melt and mix huge rock masses.[3] However, a fair fraction of
material should have been vaporized by this impact, creating a rock-vapor atmosphere around the
young planet. The rock-vapor would have condensed within two thousand years, leaving behind hot
volatiles which probably resulted in a heavy carbon dioxide atmosphere with hydrogen and water vapor
. Liquid water oceans existed despite the surface temperature of 230°C because of the atmospheric
pressure of the heavy CO2 atmosphere. As cooling continued,subduction and dissolving in ocean water
removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles
appeared.[4]
should have caused melting of one or two large areas. Present composition does not match complete
melting and it is hard to completely melt and mix huge rock masses.[3] However, a fair fraction of
material should have been vaporized by this impact, creating a rock-vapor atmosphere around the
young planet. The rock-vapor would have condensed within two thousand years, leaving behind hot
volatiles which probably resulted in a heavy carbon dioxide atmosphere with hydrogen and water vapor
. Liquid water oceans existed despite the surface temperature of 230°C because of the atmospheric
pressure of the heavy CO2 atmosphere. As cooling continued,subduction and dissolving in ocean water
removed most CO2 from the atmosphere but levels oscillated wildly as new surface and mantle cycles
appeared.[4]
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.[5][6][7] This requires the presence of an atmosphere. The Cool Early Earth
theory covers a range from about 4.4 Ga to 4.0 Ga.
the formation of the Earth.[5][6][7] 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.[8]
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.[8]
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