Thermal history of the Earth
The thermal history of the Earth is the study of the cooling history of Earth's interior. It is a sub-field of geophysics. Thermal histories are also computed for the internal cooling of other planetary and stellar bodies. The study of the thermal evolution of Earth's interior is uncertain and controversial in all aspects, from the interpretation of petrologic observations used to infer the temperature of the interior, to the fluid dynamics responsible for heat loss, to material properties that determine the efficiency of heat transport.
Observations that can be used to infer the temperature of Earth's interior range from the oldest rocks on Earth to modern seismic images of the inner core size. Ancient volcanic rocks can be associated with a depth and temperature of melting through their geochemical composition. Using this technique and some geological inferences about the conditions under which the rock is preserved, the temperature of the mantle can be inferred. The mantle itself is fully convective, so that the temperature in the mantle is basically constant with depth outside the top and bottom thermal boundary layers. This is not quite true because the temperature in any convective body under pressure must increase along an adiabat, but the adiabatic temperature gradient is usually much smaller than the temperature jumps at the boundaries. Therefore, the mantle is usually associate with a single or potential temperature that refers to the mid-mantle temperature extrapolated along the adiabat to the surface. The potential temperature of the mantle is estimated to be about 1350 C today. There is an analogous potential temperature of the core but since there are no samples from the core its present-day temperature relies on extrapolating the temperature along an adiabat from the inner core boundary, where the iron solidus is somewhat constrained.
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The simplest mathematical formulation of the thermal history of Earth's interior involves the time evolution of the mid-mantle and mid-core temperatures. To derive these equations one must first write the energy balance for the mantle and the core separately. They are,
for the mantle, and
for the core. is the surface heat flow [W] at the surface of the Earth (and mantle), is the secular cooling heat from the mantle, and , , and are the mass, specific heat, and temperature of the mantle. is the radiogenic heat production in the mantle and is the heat flow from the core mantle boundary. is the secular cooling heat from the core, and and are the latent and gravitational heat flow from the inner core boundary due to the solidification of iron.
Solving for and gives,
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The thermal catastrophe of the Earth can be demonstrated by solving the above equations for the evolution of the mantle with . The catastrophe is defined as when the mean mantle temperature exceeds the mantle solidus so that the entire mantle melts. Using the geochemically preferred Urey ratio of and the geodynamically preferred cooling exponent of the mantle temperature reaches the mantle solidus (i.e. a catastrophe) in 1-2 Ga. This result is clearly unacceptable because geologic evidence for a solid mantle exists as far back as 4 Ga (and possibly further). Hence, the thermal catastrophe problem is the foremost paradox in the thermal history of the Earth.
- Boehler, Reinhard (1996). "MELTING TEMPERATURE OF THE EARTH'S MANTLE AND CORE: Earth's Thermal Structure". Annual Review of Earth and Planetary Sciences 24 (1): 15–40. Bibcode:1996AREPS..24...15B. doi:10.1146/annurev.earth.24.1.15.
- Davies, Geoffrey F. (2001). Dynamic earth : plates, plumes and mantle convection (Repr. ed.). Cambridge: Cambridge University Press. ISBN 9780521599337.
- Fowler, C.M.R. (2006). "7. Heat". The solid earth : an introduction to global geophysics (2nd ed.). Cambridge, UK: Cambridge University Press. pp. 269–325. ISBN 9780521893077.
- Jacobs, J.A. (1992). "4. The thermal history of the Earth". Deep interior of the earth (1st ed.). London: Chapman & Hall. ISBN 9780412365706.
- McKenzie, Dan; Weiss, Nigel (1975). "Speculations on the Thermal and Tectonic History of the Earth". Geophysical Journal of the Royal Astronomical Society 42 (1): 131–174. doi:10.1111/j.1365-246X.1975.tb05855.x.
- Pollack, Henry N.; Hurter, Suzanne J.; Johnson, Jeffrey R. (1993). "Heat flow from the Earth's interior: Analysis of the global data set". Reviews of Geophysics 31 (3): 267. Bibcode:1993RvGeo..31..267P. doi:10.1029/93RG01249.
- Sharpe, H. N.; Peltier, W. R. (1978). "Parameterized mantle convection and the Earth's thermal history". Geophysical Research Letters 5 (9): 737–740. Bibcode:1978GeoRL...5..737S. doi:10.1029/GL005i009p00737.
- Williams, Quentin (6 October 1997). "Why is the earth's core so hot? And how do scientists measure its temperature?". Ask the experts. Scientific American. Retrieved 6 April 2013.