Scientists from The Australian National University (ANU) have uncovered a doughnut-shaped zone located thousands of kilometers beneath the Earth’s surface within its liquid core, shedding light on the workings of our planet’s magnetic field.
This newly identified structure exists only in low-latitude areas and runs parallel to the equator. According to seismologists at ANU, it has previously gone unnoticed.
The Earth contains two core layers: a solid inner core and a liquid outer core. The mantle surrounds the core. The newly found doughnut-shaped area lies at the top of the outer core, right where the liquid core interfaces with the mantle.
Professor Hrvoje Tkalčić, a co-author of the study and geophysicist at ANU, noted that the seismic waves within this newly discovered area travel at a slower speed compared to those in the rest of the outer core.
“This region is aligned with the equatorial plane, restricted to low latitudes, and it has a doughnut shape,” he explained.
“We can’t determine its exact thickness, but we estimate it extends several hundred kilometers below the core-mantle boundary.”
Instead of employing conventional seismic wave observation methods that focus on signals from earthquakes in the first hour, ANU scientists examined the similarities in waveforms many hours post-earthquake, leading to this unique finding.
“By analyzing the paths of these waves and how they navigate through the outer core, we were able to reconstruct their travel times, clearly showing that this newly identified region exhibits lower seismic speeds,” Professor Tkalčić stated.
“The unusual structure remained unnoticed until this point because earlier studies obtained data with limited coverage of the outer core by only observing waves typically within the first hour following major earthquakes.”
“We achieved improved volumetric coverage since we studied the reverberating waves for several hours after significant earthquakes.”
Dr. Xiaolong Ma, another co-author of the study, mentioned that this discovery helps unravel some enigmas relating to the dynamics of Earth’s magnetic field.
“Many aspects of the outer core’s behavior still pose questions, necessitating a collaborative approach from fields like seismology, mineral physics, geomagnetism, and geodynamics,” Dr. Ma remarked.
The outer core primarily consists of liquid iron and nickel. The intense movement of this electrically conductive liquid generates the Earth’s magnetic field, which encircles our planet, safeguarding all living organisms from harmful solar winds and radiation.
Researchers believe that gaining a deeper understanding of the outer core’s composition, including lighter chemical elements, is essential for grasping the magnetic field and forecasting potential shifts or reductions in its strength.
“Our results are noteworthy as the low speed of seismic waves within the liquid core suggests a high concentration of lighter chemical elements in these areas, which contribute to their slower speeds. These light elements, combined with temperature variations, aid in stirring the liquid in the outer core,” Professor Tkalčić elaborated.
“The magnetic field is crucial for sustaining life on Earth’s surface.”
“The dynamics of Earth’s magnetic field is a subject of great interest in the scientific community, so our findings may encourage further investigation into magnetic fields both on Earth and other celestial bodies.”
The research has been published in Science Advances.
