We show that antineutrino $\left({\overline{v}}_e\right)$ spectroscopy in upcoming detectors in Italy and Japan can be used to measure the separate global abundances of ${}^{238}\mathrm{U}$ and ${}^{232}\mathrm{Th}$, thus $\sim 90\%$ of the radiogenic heat in the Earth. Exploiting the unique advantage of their contrasting geological locations, they may also probe differences in U,Th areal densities in the continental and oceanic crusts and the mantle. Bearing directly on the interior of the whole Earth, such data can test, for the first time, the conceptual foundations of the geophysical structure, dynamics, and evolution of the present Earth.

• Received 15 August 1997

DOI:https://doi.org/10.1103/PhysRevLett.80.635