Earth
Heat

Isotope
Heat release W/kg isotope
Half-life years
Mean mantle concentration kg isotope/kg mantle
Heat release W/kg mantle
238U
94.6×10−6
4.47×109
30.8×10−9
2.91×10−12
235U
569×10−6
0.704×109
0.22×10−9
0.125×10−12
232Th
26.4×10−6
14.0×109
124×10−9
3.27×10−12
40K
29.2×10−6
1.25×109
36.9×10−9
1.08×10−12

Question: Which isotopes in the Earth are heat-producing?
Answer: The heat-producing isotopes in the Earth are potassium-40, uranium-238, and thorium-232.