Earth's internal heat budget
Earth's internal heat budget is fundamental to the
Earth's internal heat travels along
Despite its geological significance, Earth's interior heat contributes only 0.03% of
Global data on heat-flow density are collected and compiled by the International Heat Flow Commission of the International Association of Seismology and Physics of the Earth's Interior.[9]
Heat and early estimate of Earth's age
Based on calculations of Earth's cooling rate, which assumed constant conductivity in the Earth's interior, in 1862
Global internal heat flow
Estimates of the total heat flow from Earth's interior to surface span a range of 43 to 49 terawatts (TW) (a terawatt is 1012 watts).[13] One recent estimate is 47 TW,[1] equivalent to an average heat flux of 91.6 mW/m2, and is based on more than 38,000 measurements. The respective mean heat flows of continental and oceanic crust are 70.9 and 105.4 mW/m2.[1]
While the total internal Earth heat flow to the surface is well constrained, the relative contribution of the two main sources of Earth's heat, radiogenic and primordial heat, are highly uncertain because their direct measurement is difficult. Chemical and physical models give estimated ranges of 15–41 TW and 12–30 TW for
The
Earth heat transport occurs by
Sources of heat
Radiogenic heat
The
For the Earth's core,
Isotope | Heat release W/kg isotope |
Half-life years |
Mean mantle concentration kg isotope/kg mantle |
Heat release W/kg mantle |
---|---|---|---|---|
232Th | 26.4×10−6 | 14.0×109 | 124×10−9 | 3.27×10−12 |
238U | 94.6×10−6 | 4.47×109 | 30.8×10−9 | 2.91×10−12 |
40K | 29.2×10−6 | 1.25×109 | 36.9×10−9 | 1.08×10−12 |
235U | 569×10−6 | 0.704×109 | 0.22×10−9 | 0.125×10−12 |
Geoneutrino detectors can detect the decay of 238U and 232Th and thus allow estimation of their contribution to the present radiogenic heat budget, while 235U and 40K are not thus detectable. Regardless, 40K is estimated to contribute 4 TW of heating.[22] However, due to the short half-lives the decay of 235U and 40K contributed a large fraction of radiogenic heat flux to the early Earth, which was also much hotter than at present.[14] Initial results from measuring the geoneutrino products of radioactive decay from within the Earth, a proxy for radiogenic heat, yielded a new estimate of half of the total Earth internal heat source being radiogenic,[22] and this is consistent with previous estimates.[21]
Primordial heat
Primordial heat is the heat lost by the Earth as it continues to cool from its original formation, and this is in contrast to its still actively-produced radiogenic heat. The Earth core's heat flow—heat leaving the core and flowing into the overlying mantle—is thought to be due to primordial heat, and is estimated at 5–15 TW.[23] Estimates of mantle primordial heat loss range between 7 and 15 TW, which is calculated as the remainder of heat after removal of core heat flow and bulk-Earth radiogenic heat production from the observed surface heat flow.[13]
The early formation of the Earth's dense core could have caused superheating and rapid heat loss, and the heat loss rate would slow once the mantle solidified.[23] Heat flow from the core is necessary for maintaining the convecting outer core and the geodynamo and Earth's magnetic field; therefore primordial heat from the core enabled Earth's atmosphere and thus helped retain Earth's liquid water.[21]
Heat flow and tectonic plates
Controversy over the exact nature of mantle convection makes the linked evolution of Earth's heat budget and the dynamics and structure of the mantle difficult to unravel.[21] There is evidence that the processes of plate tectonics were not active in the Earth before 3.2 billion years ago, and that early Earth's internal heat loss could have been dominated by advection via heat-pipe volcanism.[24] Terrestrial bodies with lower heat flows, such as the Moon and Mars, conduct their internal heat through a single lithospheric plate, and higher heat flows, such as on Jupiter's moon Io, result in advective heat transport via enhanced volcanism, while the active plate tectonics of Earth occur with an intermediate heat flow and a convecting mantle.[24]
See also
- Geothermal energy
- Geothermal gradient
- Planetary differentiation
- Thermal history of the Earth
- Anthropogenic heat
External links
Media related to Earth's internal heat budget at Wikimedia Commons
References
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- ^ ISBN 978-0-521-66624-4.
- ^ Buffett, B. A. (2007). Taking Earth's temperature. Science, 315(5820), 1801–1802.
- ^ Morgan Bettex (25 March 2010). "Explained: Dynamo Theory". MIT News.
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- ^ Lowrie, W. (2007). Fundamentals of geophysics. Cambridge: CUP, 2nd ed.
- ^ www.ihfc-iugg.org IHFC: International Heat Flow Commission – Homepage. Retrieved 18/09/2019.
- ^ Thomson, William. (1864). On the secular cooling of the earth, read 28 April 1862. Transactions of the Royal Society of Edinburgh, 23, 157–170.
- ^ ISBN 978-0-08-055247-7.
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- ^ a b c Dye, S. T. (2012). Geoneutrinos and the radioactive power of the Earth. Reviews of Geophysics, 50(3). doi:10.1029/2012RG000400
- ^ a b Arevalo Jr, R., McDonough, W. F., & Luong, M. (2009). The K/U ratio of the silicate Earth: Insights into mantle composition, structure and thermal evolution. Earth and Planetary Science Letters, 278(3), 361–369.
- ^ Jaupart, C., & Mareschal, J. C. (2007). Heat flow and thermal structure of the lithosphere. Treatise on Geophysics, 6, 217–251.
- ^ Korenaga, J. (2003). Energetics of mantle convection and the fate of fossil heat. Geophysical Research Letters, 30(8), 1437.
- ^ "How much of the heat dissipated into space by Earth is due to radioactive decay of its elements? About half is due to this "radiogenic heat"". Stanford University. 2015. Archived from the original on 25 June 2017.
- ^ a b Korenaga, J. (2011). Earth's heat budget: Clairvoyant geoneutrinos. Nature Geoscience, 4(9), 581–582.
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- ^ a b c d Korenaga, J. (2008). Urey ratio and the structure and evolution of Earth's mantle. Reviews of Geophysics, 46(2).
- ^ a b Gando, A., Dwyer, D. A., McKeown, R. D., & Zhang, C. (2011). Partial radiogenic heat model for Earth revealed by geoneutrino measurements. Nature Geoscience, 4(9), 647–651.
- ^ a b Lay, T., Hernlund, J., & Buffett, B. A. (2008). Core–mantle boundary heat flow. Nature Geoscience, 1(1), 25–32.
- ^ a b c Moore, W. B., & Webb, A. A. G. (2013). Heat-pipe Earth. Nature, 501(7468), 501–505.
- ^ Pease, V., Percival, J., Smithies, H., Stevens, G., & Van Kranendonk, M. (2008). When did plate tectonics begin? Evidence from the orogenic record. When did plate tectonics begin on planet Earth, 199–208.
- ^ Stern, R. J. (2008). Modern-style plate tectonics began in Neoproterozoic time: An alternative interpretation of Earth’s tectonic history. When did plate tectonics begin on planet Earth, 265–280.