We Now Know What Earth's Inner Core Is Made Of


Robin Andrews

Science & Policy Writer


The inner core, outer core, mantle, and crust of our world. Vadim Sadovski/Shutterstock

Just recently, scientists discovered a continent-sized liquid metal “dragon” making its way around the Earth’s outer core. Now, it seems as if the inner core is taking center stage, as researchers have finally found out what it’s completely made of.

Presenting their results at the recent annual gathering of the American Geophysical Union in San Francisco, the team from Tohoku University reaffirm that the solid ball of metal at our planet’s heart is indeed mostly comprised of iron, with a bunch of nickel thrown in too. However, based on a series of laboratory experiments, they are confident that there’s also a trace of silicon too.


“We believe that silicon is a major element – about 5% [of the Earth's inner core] by weight could be silicon dissolved into the iron-nickel alloys,” lead researcher Eiji Ohtani, a professor of petrology and geophysics at Tohoku University, told BBC News.

About 1.5 billion years ago, the Earth had an unfathomably hot core that was violently losing heat. Then, after having cooled sufficiently, part of it solidified and sunk beneath the ocean of the rest of it, taking much of the planet’s iron and nickel with it. Thus, the inner core and the outer core were born.

Based on our understanding of geochemical processes and seismic surveys, we’ve got a pretty good understanding of the primary components of each layer of our planet, including the inner core. It’s clear that in order to have the current balance of elements that Earth has further up, the core must be 85 percent iron and 10 percent nickel.

That has meant that 5 percent of it has remained up for grabs, so to speak, to anyone who can come up with a convincing enough theory. Some of the candidates put forward have been oxygen, silicon, and sulfur.


Silicon in its pure elemental form, a vital component of our electronic systems. Enricoros/Wikimedia Commons; Public Domain

This particular team of researchers used experimental devices to recreate the very same pressures and temperatures that can be found at Earth’s core. That’s about 5,400°C (9,800°F) – the same temperature as the surface of the Sun – and 3.6 million times more pressurized than Earth’s surface.

By adding silicon to core-like mixtures of iron and nickel, they found that they could recreate the same materials as hinted at by previous seismic surveys. More work is required, and other elements (notably oxygen) have not yet been ruled out, but it’s looking like silicon is the element they’re looking for.

The solid inner core is 2,440 kilometers (1,500 miles) across, about the size of Pluto. Its interaction with the turbulent outer core drives an enormous dynamo that gives our planet its life-shielding magnetic field. So the more we know about it, the better, and this paper has been rather splendid in this regard by potentially having solved a long-standing puzzle.


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  • magnetosphere,

  • earth,

  • solid,

  • iron,

  • experiments,

  • silicon,

  • composition,

  • inner core,

  • nickel