A recent study reveals a new, distinct fifth layer of Earth deep inside the core, which could help us understand its magnetic field.
For years, we have been taught that the Earth has four layers: a thin outer shell of rock that we live on known as the crust; the mantle, where rocks flow like an extremely viscous liquid, driving the movement of continents and the lifting of mountains; a liquid outer core of iron and nickel that generates the planet’s magnetic field; and a solid inner core.
Now, scientists have revealed a new, distinct layer within our planet’s inner core, which could help in our understanding of the evolution of Earth’s magnetic field, reports the Washington Post.
In a study published this week in Nature Communications, a pair of seismologists at the Australian National University documented new evidence of a 400-mile-thick solid metallic ball at the center of Earth’s inner core.
“We have now confirmed the existence of the innermost inner core,” said one of the scientists, Hrvoje Tkalcić, a professor of geophysics at the Australian National University in Canberra.
“Clearly, the innermost inner core has something different from the outer layer,” said Thanh-Son Pham, lead author of the study. “We think that the way the atoms are [packed] in these two regions are slightly different.”
So how did the two scientists figure out there was another, solid core? The seismologists analyzed the crisscrossing of seismic waves from large earthquakes, and it took some time.
Scientists study the inner core to better understand Earth’s magnetic field, which protects us from harmful radiation in space and helps make life possible on our home planet.
To be fair, Two Harvard seismologists, Miaki Ishii and Adam Dziewonski, first proposed the idea of the innermost inner core in a study published in 2002 in the journal PNAS. based on peculiarities in the speed of seismic waves passing through the inner core.
Scientists already knew that the speed of seismic waves traveling through this part of the Earth varied depending on the direction. The waves traveled fastest when going from pole to pole along the Earth’s axis and slowest when traveling perpendicular to the axis.
But in a small region at the center, the slowest waves were those traveling at a 45-degree angle to the axis instead of 90 degrees, the Harvard seismologists said. So being that the data at that time was too s-parse, the theory of the new central core didn’t amount to much.
The inner core was discovered by Danish seismologist Inge Lehmann in 1936. Since that discovery, seismologist5s have learned the Inner core makes up less than 1 percent of Earth’s volume (Earth’s center is located about 4,000 miles below the surface).
We don’t have the instruments to actually get direct measurements, but scientists measure shock waves triggered by earthquakes to get indirect readings. When a large earthquake strikes, the resulting shock waves, or seismic waves, can bounce back and forth from one side of the Earth to the other like a ping-pong ball.
In the new study, the scientists took advantage of the fact that seismic waves also bounce back. Thus a seismometer close to the epicenter could detect the reflection of the wave that traveled through the Earth and bounced back, passing through the innermost inner core twice.
In recent years, with the multitude of seismographs deployed, especially in the U.S., combining signals from multiple instruments enabled the detection of the faint reflections resulting from earthquakes with a magnitude of 6 or larger, reports the New York Times.
“We processed 200 events and found that 16 of them had these bouncing waves,” Dr. Tkalcic said.
“The breakthrough in this study is that we find a new way to sample the very center of the Earth’s inner core,” Pham said. The team, he said, has even more evidence to prove the “innermost inner core actually exists.”
