Title: Implications of Neutrino Geophysics to the Earth Sciences

Abstract: Neutrino geophysics has the potential to provide hard constraints on questions relating to the formulation, evolution, and long-term habitability of planets. For the immediate future, the unwieldy logistics of neutrino detection mandates asking simple questions and taking advantage of what is already known about the Earth. With regard to antineutrinos generated by U and Th decay, it is productive to partition the earth into continental crust, mantle (including the oceanic crust), and the core (which is expected to have no U or Th). The continents are complexly heterogeneous and much more radioactive that the mantle. Their effect on the computed mantle radioactivity can be lessened by having the antineutrino detector in the middle of an ocean basin or by having two detectors different distances from a continental margin. The amount of radioactive heat production of some continental locations, like South Africa, is known from studies of rocks (called xenoliths) brought up by diamond pipes that give temperature and hence heat flow as a function of depth. Radioactive heat production balances the difference between surface and mantle heat flow as these stable regions are near steady state. Once antineutrino studies yield the U and Th concentration in the mantle, arguments by geochemists traditionally used to constrain them can be turned around. The cooling rate of the Earth's interior (a topic dating back to Lord Kelvin) controls the duration of active tectonics on our planet. Knowing average U and Th concentrations calibrates models of mantle melting beneath midoceanic ridges and cosmochemical models of the Earth's accretion from the solar nebula. In more detail, several antineutrino detectors would tell if the mantle was laterally heterogeneous with a thick layer of dregs in the lower 1000 km. Potassium detectors would tell if there is a significant hidden reservoir of this element in the deep mantle or core. X-raying the Earth with neutrinos provides valuable information when combined with seismic data. The studies take advantage of the fact that neutrinos move in known straight lines while the paths of seismic waves are not known precisely. The absolute depth to the Earth's core is a potential application.