Theres a small problem with Earths magnetic field: It should not have existed, as Earths rock record indicates it has, for the past 3.5 billion years. Motions in the Earths molten iron core generate convection currents--similar to boiling water--which produce the field. Many sources of heat drive these currents, but the known sources seem inadequate to maintain the field this long. In 1971 University of Minnesota geology and geophysics professor Rama Murthy theorized that radioactive potassium in the core could supply additional heat, but researchers investigating that claim have been unable to obtain reliable experimental data. In a paper to be published Thursday (May 8) in Nature, Murthy presents experimental evidence for his idea and shows why other researchers have been unable to corroborate it.
The work helps explain how Earth has maintained its magnetic field, which shields the planet from harmful cosmic rays and the constant stream of charged particles from the sun known as the solar wind.
"Earth is losing energy from its surface at a rate of about 44 trillion watts," Murthy said. "About 75 percent is heat from the mantle [the middle layer, composed of rock], and 20 to 25 percent is heat from the core. Measurements of cooling at the core-mantle boundary show too much loss for a core to maintain heat and a magnetic field for 3.5 billion years." But if radioactive elements such as potassium, and perhaps uranium and thorium, also exist in the core, the heat from their radioactivity could keep the core hot enough to move and maintain the magnetic field, he said.
Deane Morrison | EurekAlert!
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