Most of us learned in school that the Earth has four layers in its internal structure: the crust, the mantle, the outer core, and the inner core. But recent research reveals that the inner core itself has layers, and that there is a fifth layer to this picture. The innermost inner core is thought to be a solid metallic ball around 400 miles across, according to seismologists from the Australian National University.
By studying the seismic waves that pass through the planet during events like earthquakes, seismologists can learn about the interior of the planet. For decades, scientists have debated whether the planet has a solid ball within the inner core, which is composed of an iron-nickel alloy. Now, the researchers say they have support for this idea from studying around 200 earthquakes, each of which created seismic waves that bounced off the core.
Dispatches From The Front 