The Earth's interior radiates approximately 46 terawatts (TW, 1012 J s-1) of heat (total combined production of nuclear power today is about 1 TW of energy). The Earth's thermal energy comes from the cooling of the planet, minor contributions from tidal friction and inner core growth, and significantly from the decay of radioactive elements. The exact proportional contribution of these heat supplies is unknown. Plate tectonics is the primary manifestation of heat transport within the Earth today. Large tectonic plates are produced at mid-ocean ridges and transported across the surface of the globe to deep ocean trenches, where they plunge into the Earth's interior sending cold slabs into the interior and cooling the planet. In order to better understand the dynamic processes that occur both within the solid Earth as well as on the planet's surface, we must develop a comprehensive model of Earth composition and structure that is internally consistent with observations from the fields of geology, geochemistry, geophysics and particle physics. The abundance and distribution of naturally-occurring radioactive elements is integral to the understanding of Earth dynamics, as radiogenic heat provides a key source of energy that serves to drive mantle convection, plate tectonics and the evolution of the entire planet.
The primary objectives of the proposed research are to: (1) understand the nature and three-dimensional distribution of naturally-occurring radioactive elements in the Earth, particularly potassium, thorium and uranium, which produce >99% of all radiogenic heat in the Earth; (2) develop an internally consistent model of the Earth, including the thermal constitution and evolution of the planet; and, (3) build Earth models that can be tested against data from newly developed antineutrino detectors. (Antineutrinos are neutral nuclear particles produce during beta-decay of radioactive elements.) The proposed work plan involves dynamic modeling to determine the geometry, distribution and chemical composition of the Earth's major reservoirs, namely the continental crust, mantle and metallic core. Model results will be interpreted in conjunction with antineutrino data in order to develop a comprehensive, three-dimensional model of Earth composition and structure.
for the advancement of neutrino geosciences. This nascent field of study uses the measured flux of antineutrinos from the decay products of uranium and thorium within the earth to address fundamental questions in geology regarding the quantity and distribution of heat-production in our planet. A significant outcome of this project is cross disciplinary development, resulting in geologists learning neutrino physics and particle physicists learning geology. Evidence of this learning is manifest in geologists publishing in physics journals (W.F. McDonough et al. 2012, The many uses of electron antineutrinos, Physics Today 65, 46; O. Sramek et al. 2012, Geoneutrinos, Advances in High Energy Physics 2012, 235686) and particle physicists publishing in geology journals (S.T. Dye 2010, Geo-neutrinos and silicate earth enrichment of uranium and thorium, Earth and Planetary Science Letters 297, 1; S.T. Dye 2012 Geo-neutrinos and the radioactive power of the earth, Reviews of Geophysics 50, RG3007). A major outcome of intellectual merit that resulted from this project is the dissemination of the idea of Ved Lekic and Edwin Kite to use geo-neutrinos to explore the uranium and thorium content of seismically resolved structures in the deep mantle. Under the direction of project PIs (Dye, McDonough, Zhong), O. Sramek completed the analysis and published the results (O. Sramek et al. 2013, Geophysical and geochemical constraints on geoneutrino fluxes from Earth’s mantle, Earth and Planetary Science Letters 361, 356). A major outcome of broader impact that resulted from this project is the Nature News article by Alexandra Witze on 2 April 2013 (Detectors zero in on Earth's heat, geoneutrinos paint picture of deep mantle processes), reporting on results presented at Neutrino Geosciences 2013 at Takayama, Japan. The article quotes project PIs Dye and McDonough, who attended and helped organize the workshop.
