Estimate the yearly heat production due to the Earth’s present ⁴⁰K content, assuming B^- decay is the dominant mode of radioactive decay (Q= 1.32 MeV/atom decayed). How does this compare with the global heat loss due to seafloor spreading, of ~10²⁰ cal/yr? 1 eV = 3.8 x 10^‑20 cal; mean bulk earth K content = 170 ppm; B^-   decay constant = 4.9 x 10^‑10 Y^‑1; mean ⁴⁰K abundance 0.012% of ³⁹K.