An Experimental Journey to the Center of the Earth Yields Clues to Make-up of Planet’s Core

January 10, 2017 | Maggie Romuld

Photo credit: NASA/Goddard Space Flight Center/Reto Stöckli

Japanese scientists believe Silicon should be added to the list of major elements in the Earth’s core. 

Scientists have long believed—and largely agreed—that the Earth’s core is made up primarily of iron (85 percent), with 10 percent nickel and some lighter elements, such as carbon, oxygen, silicon, or sulfur mixed in.

There has been considerable debate, however, about the amount and chemistry of the lighter elements.  Scientists from Tohoku University, in Japan, now believe they have unearthed one of the mystery elements. Their experiments suggest the most likely candidate is silicon.

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It’s not possible to study the interior of the planet directly, so scientists create experiments where they can compare known seismic properties of the Earth’s core with the seismic signature of iron-rich light element alloys.

To investigate the unaccounted-for five percent of the core, lead researcher Eiji Ohtani and his team created alloys of iron and nickel and mixed them with silicon. After subjecting them to the pressure and temperature conditions that exist in the inner core, they found that their mixture matched what had been calculated for the Earth's interior.

Professor Ohtani told BBC News: "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." He also added that more work was needed to confirm the presence of silicon, and that their results did not rule out the presence of other elements.

Other scientists have suggested that oxygen may be a key component of the Earth’s interior. In 2014, PhysOrg reported that “Researchers offer 'proof' that oxygen is the only light element in the Earth's core.” A team of researchers from France, Switzerland, and the U.K., used seismic data, lab experiment results, and theoretical calculations to offer proof that oxygen is present in the Earth's interior.

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In a paper published in Proceedings of the National Academy of Sciences, the team described how their calculations suggested that oxygen makes up 3.7 percent of the outer core. They found no oxygen-free composition that fit the seismological data, and said their results indicated that oxygen is always required in the outer core. In addition, their testing indicated that the outer core is also made up of 1.9 percent silicon, and that there is no carbon or sulfur.

It is clear that much more research is needed on this topic, but the science is intriguing. And though the results are far from definitive, they do add to our understanding of the formation of the Earth and its deep past.

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