Scientists Discover Earth's Fiery Core is as Hot as the Surface of the Sun

It turns out that our planet's core is a lot hotter than we ever expected. Researchers have discovered that the temperature of the Earth's center is about 1,000 degrees hotter than previously thought, making the fiery core as hot as the surface of the Sun.

The Earth's core is made of a sphere of liquid iron at temperatures above 4,000 degrees and pressures of more than 1.3 million atmospheres. Under these conditions, iron is as liquid as the water in our oceans. Yet it's only at the very center of the Earth, where pressure and temperature rise even higher, that the liquid iron becomes solid.

In order to further examine this solid core, researchers analyzed earthquake-triggered seismic waves that passed through the Earth. These told them how pressure in the Earth increases with depth, but did not tell them information on temperature. In order to further investigate temperature, which has an important influence on the movement of material within the liquid core and the solid mantle, scientists turned to the laboratory.

The researchers looked at the melting point of iron at different pressures using a diamond anvil cell to compress speck-sized samples to pressures of several million atmospheres. They then employed powerful laser beams to heat these specks to 4,000 or even 5,000 degrees Celsius.

"In practice, many experimental challenges have to be met as the iron sample has to be insulated thermally and also must not be allowed to chemically react with its environment." said Agnes Dewaele from CEA in a news release. "Even if a sample reaches the extreme temperatures and pressures at the center of the Earth, it will only do so for a matter of seconds. In this short timeframe it is extremely difficult to determine whether it has started to melt or is still solid."

In order to get around that issue, the researchers used X-rays to probe a sample and deduce whether it was solid, liquid or partly molten within. The new technique that they employed could make the determination in as little as a second--a short enough time to keep temperature and pressure constant while avoiding any chemical reactions.

So what did they find? The researchers discovered that starting at 2,400 degrees, recrystallization effects appear on the surface of the iron samples, leading to dynamic changes of the solid iron's crystalline structure. This meant that above those temperatures, the core was solid rather than molten. By examining the states of iron, they were also able to estimate that the Earth's core is about 6,000 C, give or take 500 C--about as hot as the surface of the Sun.

"We are, of course, very satisfied that our experiment validated today's best theories on heat transfer from the Earth's core and the generation of the Earth's magnetic field," said Dewaele in a news release. "I am hopeful that in the not-so-distant future, we can reproduce in our laboratories, and investigate with synchrotron X-rays every state of matter inside Earth."

The findings are published in the journal Science.