By traveling to the center of the Earth via seismic waves, scientists discovered a ring-like structure within the swirling pool of molten metal known as the outer core.
Research published in the journal Science Advances identified a doughnut-shaped region within the outer core, parallel to the equator.
A study co-author and Australian National University geophysicist Prof Hrvoje Tkalčić said because scientists could not reach the core with current technology, the team analyzed the shapes of seismic waves generated by large earthquakes as they traveled through it.
They found that the waves slowed down as they passed through a section near the ceiling, in front of the mantle. “By understanding the geometry of the waves’ paths and how they traverse the outer core’s volume, we reconstructed their travel times through the Earth,” said Tkalčić.
“We realized that seismic waves slow down in the zone mathematically called a torus.”
To most people, it looked like a doughnut, he said.
Understanding the outer core was important, he said, as it was critical to the survival of life on the surface. It was responsible for the magnetic field, who protected the earth from the constant bombardment of charged particles from the sun.
Current moving within the molten iron and nickel acted like a “giant dynamo” that generated and maintained the Earth’s magnetic field.
Tkalčić said scientists still do not know why Earth had this active dynamo, while many other planets did not: “It is fair to say that we understand the surfaces of other planets in more detail than our own planet inside.”
Earth’s interior — a solid center containing the inner core, enveloped by a liquid outer core and then the mantle — was just as large, he said.
Overall, the core was slightly larger than Mars. “We can think of it as a planet within our own planet,” Tkalčić said.
He added: “We don’t know the exact thickness of the doughnut, but we infer that it reaches several hundred kilometers below the core-mantle boundary.” The structure’s driving force indicates the presence of lighter chemical elements such as silicon, sulphur, oxygen, hydrogen or carbon.
“What makes this field really fascinating is that virtually everything we know is an inference based on the data we have on the surface,” he said.
A co-author, Dr Xiaolong Ma, said the discovery of a new structure within the outer core lifted a veil on the dynamics of the Earth’s magnetic field, yet there were “still mysteries about the Earth’s outer core that has yet to be resolved”.
