Earth's core is definitely solid, study finds

The Earth's core is definitively solid, according to new research by a team of scientists in Australia.

The research team managed to detect shear waves, or J waves, inside Earth's core. Shear waves can only travel through solid material.

"We found the inner core is indeed solid, but we also found that it's softer than previously thought," Hrvoje Tkalčić, an assistant professor of earth sciences at Australia National University, said in a news release.

The discovery, published Friday in the journal Science, could help scientists better understand Earth's beginnings.

"It turns out -- if our results are correct -- the inner core shares some similar elastic properties with gold and platinum," Tkalčić said. "The inner core is like a time capsule, if we understand it we'll understand how the planet was formed, and how it evolves."

Scientists first hypothesized Earth's core was solid in the 1930s. Ever since, seismologists have been trying to measure J waves passing through Earth's center. Unfortunately, the waves are tiny. Direct measurement is impossible.

Researchers at ANU finally developed a successful workaround. They dubbed the technique the correlation wavefield method. The method relies on a comparison of seismic signals measured by two separate receivers in the wake of an earthquake.

"We're throwing away the first three hours of the seismogram and what we're looking at is between three and 10 hours after a large earthquake happens," Tkalčic said. "We want to get rid of the big signals."

Scientists organized a vast network of seismometer pairs, linking each pair with an earthquake. The network allowed scientists to field dozens of correlations. Researchers cross-correlated the results, identifying similarities among the similarities.

"From those similarities we construct a global correlogram -- a sort of fingerprint of the earth," Tkalčic said.

The correlogram revealed the presence of J waves deep inside Earth, and scientists think more revelations are on the way.

"For instance we don't know yet what the exact temperature of the inner core is, what the age of the inner core is, or how quickly it solidifies, but with these new advances in global seismology, we are slowly getting there," Tkalčic said. "The understanding of the Earth's inner core has direct consequences for the generation and maintenance of the geomagnetic field, and without that geomagnetic field there would be no life on the Earth's surface."

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