Journey to the Center of the Earth Finds an Unfathomably Hot Core

There are some 16 million lightning storms in the world every year, according to the U.S. National Weather Service, and the average peak power output of a a single lightning stroke is about one trillion watts – or one terawatt. That’s pretty impressive, until you compare it to the heat at the core of our planet, which scientists recently have estimated to be some 44 terawatts (44 trillion watts), flowing continually from Earth’s interior into space.

The Earth’s core heat is what spreads our sea floors and moves the continents. It also melts iron in the outer core and creates the planet’s magnetic field. But where does it come from?

Using 20,000 boreholes across the globe, researchers from the Department of Energy’s California-based Lawrence Berkeley National Laboratory (Berkeley Lab) in collaboration with Japan’s KamLAND team are trying to determine exactly what causes our planet to produce such high temperatures.

According to their latest findings, published in Nature Geoscience, radioactive decay of uranium, thorium, and potassium in Earth’s crust and mantle is a principal source and, in 2005, the KamLAND research team, based in Japan, first showed that there was a way to measure the contribution directly. The trick was to catch what KamLAND dubbed geoneutrinos – or more specifically, geo-antineutrinos – emitted when radioactive isotopes decay.

“As a detector of geoneutrinos, KamLAND has distinct advantages,” commented Stuart Freedman of the Berkeley Lab’s Nuclear Science Division and a professor in the Department of Physics at the University of California at Berkeley, who leads U.S. participation.

Freedman compares looking for geo-antineutrinos to “looking for a spy in a crowd of people on the street. You can’t pick out one spy, but if there’s a second spy following the first one around, the signal is still small but it’s easy to spot.”

However, the scientists admit that they still have a long way to go. One thing that’s at least 97-percent certain is that radioactive decay supplies only about half the Earth’s heat. Other sources – primordial heat left over from the planet’s formation, and possibly others as well – must account for the rest.

Better models are likely to result when many more geoneutrino detectors are located in different places around the globe, including mid-ocean islands, where the crust is thin and local concentrations of radioactivity (not to mention, nuclear reactors) are at a minimum.

Said Freedman, “This is what’s called an inverse problem, where you have a lot of information but also a lot of complicated inputs and variables. Sorting those out to arrive at the best explanation among many requires multiple sources of data.”

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