<Tr> <Th> Isotope </Th> <Th> Heat release W / kg isotope </Th> <Th> Half - life years </Th> <Th> Mean mantle concentration kg isotope / kg mantle </Th> <Th> Heat release W / kg mantle </Th> </Tr> <Tr> <Td> U </Td> <Td> 6995946000000000000 ♠ 94.6 × 10 </Td> <Td> 7009447000000000000 ♠ 4.47 × 10 </Td> <Td> 6992308000000000000 ♠ 30.8 × 10 </Td> <Td> 6988291000000000000 ♠ 2.91 × 10 </Td> </Tr> <Tr> <Td> U </Td> <Td> 6996569000000000000 ♠ 569 × 10 </Td> <Td> 7008704000000000000 ♠ 0.704 × 10 </Td> <Td> 6990220000000000000 ♠ 0.22 × 10 </Td> <Td> 6987125000000000000 ♠ 0.125 × 10 </Td> </Tr> <Tr> <Td> Th </Td> <Td> 6995263999999999999 ♠ 26.4 × 10 </Td> <Td> 7010140000000000000 ♠ 14.0 × 10 </Td> <Td> 6993124000000000000 ♠ 124 × 10 </Td> <Td> 6988327000000000000 ♠ 3.27 × 10 </Td> </Tr>

What power source uses the earth's internal heat