| 1 | A | B | C | D | E |
| --- | --- | --- | --- | --- | --- |
| 2 | Earth - Heat |  |  |  |  |
| 3 | Isotope | Heat release W/kg isotope | Half-life years | Mean mantle concentration kg isotope/kg mantle | Heat release W/kg mantle |
| 4 | 238U | 94.6×10−6 | 4.47×109 | 30.8×10−9 | 2.91×10−12 |
| 5 | 235U | 569×10−6 | 0.704×109 | 0.22×10−9 | 0.125×10−12 |
| 6 | 232Th | 26.4×10−6 | 14.0×109 | 124×10−9 | 3.27×10−12 |
| 7 | 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.