Core Dynamics

I freely admit that I don’t spend a lot of time thinking about the Earth’s core. Living as I do on the thin outer crust of our planetary home, my focus is on the surface I inhabit and the atmosphere beyond, not on what’s happening miles below my feet.

That’s too bad, because the Earth’s inner core seems to be an interesting, and apparently somewhat quixotic, place. (It’s also the subject of some pretty cool science book-type graphics, like the one above.)

We don’t really know a lot about the Earth’s inner core, because of course no one has visited it. Based on a 1930s study of seismic waves and later confirming data, scientists believe that the inner core is a solid ball of iron and nickel. That solid core is covered by a sheath of liquid iron and other elements, and the interaction between the solid center and its liquid shell creates our planet’s magnetic field. But here’s the weird part: Because the solid inner core is separated from the rest of Earth by that liquid coating, the inner core can spin at its own pace, like a ball bearing covered by a thick layer of hot oil–without regard for what the rest of the planet is doing.

Some scientists have believed for years that the inner core rotates at a faster rate than the rest of the planet (called super-rotation), but there is a lively, ongoing debate about that. The debate has been spurred by some recent findings that the super-rotation has stopped, and that the core might now be spinning at a pace slower than the rest of the planet. If the pace of inner core spin has in fact changed, no one knows exactly why, or what causes the core rotation to slow down or speed up. Only the curious physical forces influencing that inner planet of solid metal and its interaction with its superheated liquid iron coating know for sure.

And there’s another cool element to all of this: the preferred scientific method for studying the inner core is . . . earthquakes. When earthquakes occur, seismic waves pass through the planet and, the data acquired about their variations in speed and direction can equip scientists to draw inferences about what’s happening deep inside our planet. One article described the seismic waves as serving like a kind of geological x-ray. So you can be sure that, the next time an earthquake rattles the cupboards out in California or outer Mongolia, some scientists will be eagerly monitoring the seismic waves that result, looking for more clues about Earth’s quixotic inner core.