Earth's heat

Most comes from radioactivity

Picture of a lava fountain during an eruption of Kilauea, Hawaii Lava fountain during an eruption of Kilauea, Hawaii.
Picture of the eruption of Mt. Pinatubo, 1991.
Volcanic eruptions often look like the detonation of a nuclear weapon. And it's nuclear decay within the earth that supplies much of the energy for such blasts (eruption of Mt. Pinatubo, 1991)

Picture of steam over the summit of Manam Volcano.
Earth's heat escaping. Steam over the summit of Manam Volcano.

More than half of the Earth's heat comes from the radioactive decay of materials within it, says a recent international study. The new research presents some of the most precise measurements of the Earth's radioactivity to date obtained bY observing the activity of subatomic particles — particularly uranium, thorium and potassium. The study appears in the Journal Nature Geoscience in an article entitled "Partial radiogenic heat model for Earth revealed by geoneutrino measurements."

"It is a high enough precision measurement that we can make a good estimate of the total amount of heat being produced by these fissions going on in naturally occurring uranium and thorium," said Glenn Horton-Smith, a coauthor of the study and an associate professor of physics at Kansas State University.

The measurements were made using the KamLAND neutrino detector in Japan. KamLAND, short for Kamioka Liquid-Scintillator Antineutrino Detector, is an experiment at the Kamioka Observatory, an underground neutrino observatory in Toyama, Japan. Neutrinos are neutral elementary particles that come from nuclear reactions or radioactive decay. Because of their small size, large detectors are needed to capture and measure them.

By gathering measurements of radioactive decay, the KamLAND researchers were able to observe geoneutrinos, or neutrinos from a geological source. They gathered data from 2002 to 2009.

Previous research has shown that Earth's heat output is about 44 terawatts, or 44 trillion watts. The KamLAND researchers found more than half of that — 29 terawatts — comes from radioactive decay of uranium, thorium and other materials, meaning that about 50 percent of the earth's heat comes from geoneutrinos.

The researchers estimate that the rest of the earth's heat comes from primordial sources left over when the earth formed and from other sources of heat. Earth's heat is the cause behind plate movement, magnetic fields, volcanoes and sea-floor spreading.

Picture of a lava dome fountain during the 1969 Mauna Ulu eruption of Kilauea Volcano, Hawai`i Lava dome fountain during the 1969 Mauna Ulu eruption of Kilauea Volcano, Hawai`i.