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Acoustic waves help determine the contents of the Earth’s core

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Posted November 26, 2015

We have been taught amazing facts about the core of the Earth in school. But how does science knows what is really so deep under our feet? They use seismic acoustic waves – the ones created by earthquakes. Measuring them allowed determining that 95% of the Earth’s core is liquid, but not what exactly is in that liquid. Currently scientists in Japan have conducted a number of experiments that allow to look into constitution of Earth‘s core.

During earthquakes acoustic waves travel through the Earth, which allowed scientists to figure out that 95% of the inner layers are liquid, but not what kind of liquids exactly. Image credit: riken.jp

During earthquakes acoustic waves travel through the Earth, which allowed scientists to figure out that 95% of the inner layers are liquid, but not what kind of liquids exactly. Image credit: riken.jp

Scientists now managed to measure the speed of sound in mixtures of liquid iron and carbon in extreme conditions, which helps determining approximate composition of Earth’s core. It is very important, as it gives scientists clues about how the earth was formed. It is known that this liquid core is mostly molten iron, but with density 10% too small to be just iron. To determine what other metals are lowering the density of the iron, scientists are now making a database that matches sound velocities with material composition and temperature.

This is far more difficult task than it may look, since temperature in the core range up to 5,400 °C and the pressures reach several million atmospheres. Because of how difficult these measurements are done, the database grew very slowly and scientists worked with solid metals mostly.

Now scientists managed to extend the catalogue to include the first liquid measurements taken at very high pressure. They used a diamond anvil cell technology, laser heating and a large inelastic scattering spectrometer. Surely, even with such impressive equipment they were not able to replicate conditions similar to those of the inner layers of the Earth, but they managed to extrapolate the results to be adequate.

Yoichi Nakajima, first author of the study, said: “the extrapolation gives us important insights, suggesting that at most only about 1.2% of the core, by weight, is carbon. Thus while there may be, and, in fact, probably is, some carbon in the core, there must also be some other light elements, such as silicon, oxygen, sulphur or hydrogen”. Scientists said that they will continue to do similar experiments with other materials to determine what other molten elements are deep beneath our feet.

Source: Riken

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