It’s generally well known that the innermost part of Earth is mostly iron — about 85%. Nickel accounts for about 10%. That last 5% however, has remained a bit of a mystery.
A Japanese research team has been searching for that missing element for decades and now believes that the final 5% is most likely silicon, the BBC reported. The researchers presented their results at the fall meeting of the American Geophysical Union in San Francisco last month.
The Earth’s core, which is about 3,000 kilometers (roughly 1,800 miles) below its surface, is thought to have a radius of about 1,200 kilometers. Since it’s so deep, it’s impossible to directly test it to find out precisely what the core is made of. (For comparison, the world’s deepest mines reach a depth of only about 4 kilometers.)
Silicon has been a contender as the missing element in the core for a while. Researchers knew the missing element had to be a lighter one, and silicon had been suggested many times because of its properties such as bonding well to metals.
So instead of digging, the researchers from Tohoku University created a miniature Earth — crust, mantle, core and all — in the lab.
First, they created alloys of iron and nickel and mixed them with silicon. Then they subjected those to the pressures and temperatures that exist within the core, which is about 6,000 degrees Celsius.
These conditions matched the seismic data of the Earth’s core — information from the seismic waves that emanate from near the center of the Earth. This gave the team sufficient evidence to say silicon was probably the missing element.
“These difficult experiments are really exciting because they can provide a window into what Earth’s interior was like soon after it first formed, 4.5 billion years ago, when the core first started to separate from the rocky parts of Earth,” Simon Redfern, a professor of mineral physics at the University of Cambridge, told the BBC. “But other workers have recently suggested that oxygen might also be important in the core.”
Knowing exactly what’s down there could help scientists determine the conditions that helped form the Earth.