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A Strange Brew in Middle Earth

By Kathy A SvitilAugust 1, 2003 5:00 AM


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Something odd is cooking in the center of Earth. heat from the core has sustained the geomagnetic field for 3.5 billion years, but standard calculations show the core should have long ago lost its primordial warmth. For three decades, V. Rama Murthy, a geochemist at the University of Minnesota, has argued that radioactive potassium at Earth's center keeps things toasty. The idea remains controversial (see Discover, August 2002), but now he says he has evidence to back it up.

Murthy and his colleagues combined potassium-rich silicate material, similar to the composition of the mantle, with iron and iron sulfide, thought to make up the bulk of the core. At corelike temperatures and pressures, potassium from this "mantle" entered and blended with the "core" material. The result indicates that large amounts of radioactive potassium could have migrated to the center when Earth formed. The decay of that potassium storehouse could account for the continued heat. Murthy plans further tests to determine how much potassium is in the core, how much thermal energy it provides, and whether other radioactive elements, such as uranium and thorium, are also stoking the fire.

One way to find out is to go there. David Stevenson, a Caltech geophysicist, recently grabbed headlines with a plan to blast a giant crack in the surface and pour thousands of tons of molten iron into the gap. In about a week, he says, a probe buried in the iron would sink to the core, where it could measure the temperature, pressure, and composition. Murthy isn't holding his breath. "It's an imaginative plan, but I'm not sure it's possible," he says.

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