To better understand the sources of the Earth's heat, scientists studied antineutrinos, elementary particles that, like their neutrino counterparts, only rarely interact with normal matter. Using the Kamioka Liquid-scintillator Antineutrino Detector (KamLAND) located under a mountain in Japan, they analyzed geoneutrinos — ones emitted by decaying radioactive materials within the Earth — over the course of more than seven years.
The specific amount of energy an antineutrino packs on the rare occasions one does collide with normal matter can tell scientists about what material emitted it in the first place — for instance, radioactive material from within the Earth, as opposed to in nuclear reactors. If one also knows how rarely such an antineutrino interacts with normal matter, one can then estimate how many antineutrinos are being emitted and how much energy they are carrying in total.
The researchers found the decay of radioactive isotopes uranium-238 and thorium-232 together contributed 20 trillion watts to the amount of heat Earth radiates into space, about six times as much power as the United States consumes. U.S. power consumption in 2005 averaged about 3.34 trillion watts.
As huge as this value is, it only represents about half of the total heat leaving the planet. The researchers suggest the remainder of the heat comes from the cooling of the Earth since its birth.
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