Radioactive decay of uranium, thorium, and potassium is responsible for about one-half of the heat generating by Earth's internal area, a study published in Nature Geoscience has found.

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, msnbc.com reported. U.S. power consumption in 2005 averaged about 3.34 trillion watts.

The Earth has cooled since its formation, yet the decay of radiogenic isotopes...in the planet's interior provides a continuing heat source, the international team of American, Japanese, and Dutch researchers behind the project wrote, redorbit.com reported. Further, the current total heat flux from the Earth to space is approximately 44.2 terawatts but the relative contributions from residual primordial heat and radiogenic decay remain uncertain.

In other words, the Earth, which scientists estimate is more than 4.5 billion years old, is still has a lot of cooling off to do.

In all, the roughly 44 trillion watts of heat continually flow from the Earth's interior into space. The 44 terawatts works out to 44,000 billion watts, economictimes.indiatimes.com reported. That heat is hot enough to melt iron ore in the outer core, among other physical achievements.

Scientists in the Japan-based KamLAND (Kamioka Liquid-scintillator Antineutrino Detector) collaboration first showed that there was a way to measure the contribution directly.

Previous estimates of what scientists call radiogenic heat are roughly the same as the new figure, but they were based on the inferences of Earth's chemical composition derived from analyses of meteorites, news.sciencemag.org reported.

Japan Earth Japan