Heat productivities

isotope heat productivity, A

(calories per gram per year)

U-235 4.29

U-238 0.71

natural uranium 0.73

Th-232 0.20

K-40 0.22

natural potassium 27(10⁻⁶)

Rb-87 130(10⁻⁶)

natural rubidium 36(10⁻⁶)

major rock province

U

ppm abundances

Th

ppm

K

% heat productivity, A (in 10⁻¹³ calories per cubic centimetre per second)

oceanic crust 0.42 1.68 0.69 0.71

continental shield crust (old) 1.00 4.00 1.63 1.67

continental upper crust (young) 1.32 5.28 2.15 2.20