The New York Times reports:

The inner core of the Earth appears to hold an innermost secret.

Geology textbooks almost inevitably include a cutaway diagram of the Earth showing four neatly delineated 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.

Analyzing the crisscrossing of seismic waves from large earthquakes, two Australian scientists say there is a distinctly different layer at the very center of the Earth. “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.

Dr. Tkalcic and Thanh-Son Pham, a postdoctoral researcher, estimate that the innermost inner core is about 800 miles wide; the entire inner core is about 1,500 miles wide. Their findings were published on Tuesday in the journal Nature Communications.

While the cutaway diagram appears to depict clear-cut divisions, knowledge about the deep interior of Earth is unavoidably fuzzy. It is nearly 4,000 miles to the center of Earth, and it is impossible to drill more than a few miles into the crust. Most of what is known about what lies beneath comes from seismic waves — the vibrations of earthquakes traveling through and around the planet. Think of them as a giant sonogram of Earth. [Continue reading…]