CANBERRA, Australia — The Earth appears to be more like a “Jawbreaker” candy than scientists have previously thought, a new study reveals. Researchers in Australia say they have evidence for a 400-mile-wide core within the known core of the planet. Until now, scientists believed Earth’s structure consisted of four distinct layers: the crust, the mantle, the outer core, and the inner core.
The new findings by seismologists from The Australian National University (ANU) are confirming the existence of a fifth layer!
“The existence of an internal metallic ball within the inner core, the innermost inner core, was hypothesized about 20 years ago. We now provide another line of evidence to prove the hypothesis,” says Dr. Thanh-Son Phạm from the ANU Research School of Earth Sciences in a university release.
Data captured from seismic waves caused by earthquakes are shedding new light on the deepest parts of Earth’s inner core. By measuring the different speeds at which these waves penetrate and pass through the Earth’s inner core, the researchers believe they’ve documented evidence of a distinct layer inside Earth known as the innermost inner core – a solid “metallic ball” that sits within the center of the inner core.
Scientists are tracking earthquake waves moving through the planet
“The inferred transversely isotropic inner-core model contains a ~650-km (400 mile) thick innermost ball with P-wave speeds ~4% slower at ~50° from the Earth’s rotation axis,” the researchers write in the journal Nature Communications.
P-waves are a measure of the velocity of sound waves through Earth materials with distance versus time. The ANU researchers say studying the deep interior of Earth’s inner core can tell us more about our planet’s past and evolution.
“This inner core is like a time capsule of Earth’s evolutionary history – it’s a fossilized record that serves as a gateway into the events of our planet’s past. Events that happened on Earth hundreds of millions to billions of years ago,” says Professor Hrvoje Tkalčić, also from ANU.
The researchers analyzed seismic waves that travel directly through the Earth’s center and “spit out” at the opposite side of the globe from where the earthquake occurred — also known as the antipode. The waves then travel back to the source of the quake. The ANU scientists describe this process as similar to a ping pong ball bouncing back and forth.
“By developing a technique to boost the signals recorded by densely populated seismograph networks, we observed, for the first time, seismic waves that bounce back -and forth up to five times along the Earth’s diameter. Previous studies have documented only a single antipodal bounce,” Dr. Phạm says. “The findings are exciting because they provide a new way to probe the Earth’s inner core and its centermost region.”
One of the earthquakes the scientists studied originated in Alaska. The seismic waves triggered by this quake “bounced off” somewhere in the south Atlantic Ocean, before travelling back to Alaska.
What’s shifting the speed of seismic waves?
The researchers studied the anisotropy of the iron-nickel alloy that comprises the inside of the Earth’s inner core. Anisotropy describes how seismic waves speed up or slow down through the material of the Earth’s inner core depending on the direction in which they travel. It could be caused by different arrangements of iron atoms at high temperatures and pressures or preferred alignment of growing crystals.
The team found the bouncing seismic waves repeatedly probed spots near the Earth’s center from different angles. By analyzing the variation of travel times of seismic waves for different earthquakes, the scientists infer the crystallized structure within the inner core’s innermost region is likely different to the outer layer. They say it might explain why the waves speed up or slow down depending on their angle of entry as they penetrate the innermost inner core.
According to the ANU team, the findings suggest there could have been a major global event at some point during Earth’s evolutionary timeline that led to a “significant” change in the crystal structure or texture of the Earth’s inner core.
“There are still many unanswered questions about the Earth’s innermost inner core, which could hold the secrets to piecing together the mystery of our planet’s formation,” Prof. Tkalčić concludes.
The researchers analyzed data from about 200 magnitude-6 and above earthquakes from the last decade during their study.
South West News Service writer Dean Murray contributed to this report.