Developments in Brief : Earth’s Core Hotter Than Once Thought

The temperature of the Earth’s core is several thousand degrees hotter than had been thought, geophysicists at Caltech and UC Berkeley reported this month in Science magazine.

By measuring the temperatures required to melt iron--the Earth’s core is known to be molten--at the high pressures present inside the Earth, they concluded that the core’s temperature is at least 12,000 degrees Fahrenheit. Previous estimates were no higher than 6,700 degrees.

The team, headed by Raymond Jeanloz of Berkeley and Thomas J. Ahrens of Caltech, achieved the high pressures with a 105-foot-long, 35-ton “gun” that fires a one-ounce plastic-and-tantalum bullet at speeds as high as 16,000 m.p.h.

When the bullet struck a thin film of iron deposited on an aluminum oxide block, it produced the necessary high pressure for a fraction of a second. The researchers measured the temperature of the iron with a radiometric instrument similar to the one used by astronomers to measure the temperature of stars.

The scientists also concluded that a layer outside the core acts like a pressure cooker, holding the heat in. Were it not for this layer, the Earth’s surface would be considerably hotter.