Every now and then – anywhere from hundreds of thousands of years to millions – the north and south magnetic poles actually swap places. During this reversal, the magnetic weakens, leaving the Earth without protection. (Photo : Nasa/Getty Images)

Though it is out of reach, much of the Earth's core have been classified: 85 percent is made of iron and another 10 percent is made of nickel. It's only that mysterious last five percent that had scientists stumped for so many years.

Well, now they finally figured it out: silicon.

According to a report from Phys Org, a group of researchers from different institutes in Japan cracked the puzzle of the mysterious element making up the core of the planet. They presented their findings at a recent meeting of the American Geophysical Union.

The team was able to reach their findings by actually creating virtual Earth models in laboratories and exposing these to real-life conditions including heat and pressure. This is the best way to observe the core because it's too deep to reach via digging and probes at 3,000 kilometers under the surface.

After subjecting the models to heat and pressure, scientists target it with seismic waves and compare these to seismic waves they also send to the Earth's actual core. Silicon has already been considered, but the team from Japan tested their iron, nickel and silicon core and discovered that seismic analysis had their model matching the real core, indicating they may have figured out the missing element.

Lead researcher Eiji Ohtani of Tohoku University told BBC News that more studies are necessary to confirm silicon, and the team do not rule out other elements in the mix. Still, the accomplishment is a significant one.

"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, professor of mineral physics at the University of Cambridge, explained.