A “new hidden world” discovered in Earth’s inner core

It's not just a mass of iron. A new study finds that our planet's solid core would actually vary from hard metal to semi-soft to liquid.

For more than half a century, the scientific community believed that Earth's inner core was a solid sphere of compressed iron alloy surrounded by a liquid exterior. New research, published in the journal Physics of the Earth and Planetary Interiors, has totally turned the tables: the core of our planet would vary from hard metal to semi-soft to liquid. Basically, according to the researchers, the hard core might actually be a little soft as well. "We are discovering a whole new hidden world," was the comment of Jessica Irving, a seismologist at the University of Bristol in England, who was not involved in the study, however.

Studies on the Earth's core

Although it has been known for half a century that the Earth's interior is not hollow, its core still remains unexplored directly because of its extremely high temperature and pressure. Geophysicists, to understand its composition and nature, rely on seismic waves generated by earthquakes.

By measuring these huge vibrations, scientists are able to reconstruct a picture of the planet's inner workings in a way "similar to a CT scan of a person," Irving explained. The waves are of two types: straight compression waves and wavy shear waves. Each wave can speed up, slow down or bounce back as it passes through the ground.

The discovery about the "new world" inside the Earth

The author of the research, Rhett Butler, a geophysicist at the Hawaii Institute of Geophysics and Planetology, said the discovery came about because of mismatched numbers. The scholar was looking at how seismic waves created by large earthquakes at five different locations travel through the Earth's core to the exact opposite side of the globe. But the math didn't add up: the shear waves from the earthquakes, which should have passed through a solid metal sphere, were instead deflected in some areas.

Butler knew the math of the seismic waves was correct, hence the hypothesis that the structure of the core might be different than previously described. Butler and his co-author found that the observed waves worked if, instead of being a solid ball, the core had pockets of liquid and "soft" semi-solid iron near its surface.

"We saw that not only is it not soft everywhere," he said, "but it has hard surfaces right up against molten or pasty iron. The research could potentially revolutionize our understanding of the Earth's magnetic field.

Other research has speculated instead that the Earth's core may be deforming. Our planet still has many mysteries to unravel, recently it was also discovered that the globe is slowing down its spin and becoming lighter.