Earth's core hotter than thought, hot as sun's surface

PARIS, April 26 (UPI) -- New measurements suggest the Earth's inner core is far hotter than previously thought, at 10,800 degrees F as hot as the sun's surface, French scientists say.

The Earth's core is solid, a crystalline form of iron, but the temperature at which that crystal can form has long been debated.

New experiments used X-rays to measure tiny samples of iron at extraordinary pressures in laboratories to analyze how the iron crystals form and melt.

The first such measurements in the early 1990s of iron's "melting curves" -- from which the temperature of Earth's core can be estimated -- suggested a core temperature of about 9,000 degrees Fahrenheit.

Scientists at the French research agency CEA used the European Synchrotron Radiation Facility, the source of some of the world's most intense X-rays, to re-analyze the measurements.

"It was just the beginning of these kinds of measurements so they made a first estimate ... to constrain the temperature inside the Earth," CEA researcher Agnes Dewaele said of the earlier experiments.

"Other people made other measurements and calculations with computers and nothing was in agreement. It was not good for our field that we didn't agree with each other," she told BBC News.

"We have to give answers to geophysicists, seismologists, geodynamicists -- they need some data to feed their computer models."

The researchers' new experiments yielded an estimated core temperature of about 10,800 degrees F, give or take 1,000 degrees, or about the same as the temperature of the sun's surface.

More importantly, Dewaele said, "now everything agrees."