"It seems that the Earth's core holds a deeper secret."

So began Kenneth Chang, science and technology editor for The New York Times.

Pointing out that the books of geology almost unanimously agree that the diagram of the Earth shows 4 precisely defined layers:

  • A thin outer shell of rock that we live on is called the crust.

  • And the mantle, where rocks flow as a highly viscous liquid that drives the movement of continents and the lifting of mountains.

  • and a liquid iron-nickel outer core that generates the planet's magnetic field.

  • and a solid inner core.

Zhang pointed to what two Australian scientists who analyzed the intersection of seismic waves from large earthquakes said, which is that there is a completely different layer in the center of the Earth.

"We have now confirmed the existence of the deeper inner core," said one of them - Hrvoj Tcalcic, professor of geophysics at the Australian National University in Canberra.

Dr. Tcalcic and researcher Tan Soon Pham estimate that the innermost inner core is about 800 miles across, with the entire inner core about 1,500 miles across.

Their findings were published last Tuesday in the journal Nature Communications.


Miyake Ishii and Adam Dezyonski, two Harvard seismologists, first proposed the idea of ​​a deeper inner core in 2002 based on the velocity characteristics of seismic waves passing through the inner core.

Scientists already knew that the speed of seismic waves traveling through this part of the Earth varies with direction.

The waves moved at maximum speed when moving from one pole to another along the Earth's axis, and were slowest when moving perpendicular to the axis.

Geophysicists believe that the difference in velocities - a few percent faster along the polar tracks - arises from the alignment of iron crystals in the inner core.

But in a small area in the center, the slowest waves were those traveling at an angle of 45 degrees to the axis instead of 90 degrees, the Harvard scientists said.

Zhang noted that the new research takes advantage of the fact that seismic waves also bounce back.

Thus a seismometer close to the epicenter could detect the reflection of the wave, which traveled through the Earth and bounced back, passing the innermost core twice.

These waves can also be reflected back and forth again, traveling through the innermost core four times.

He pointed to what Vernon Cormier, a professor of physics at the University of Connecticut who was not involved in the research, said that this may indicate some change in Earth's ancient past.

The inner core is fairly young, geologically speaking, Cormier said, with estimates ranging from 600 million to 1 billion years old.

This is just a small part of the planet's 4.5 billion year history.

He concluded with what other scientists said in January that the rotational speed of the inner core is changing.