AYESHA RASCOE, HOST:
What happens when you go past Earth's crust to the ooey-gooey center? Well, it's actually not ooey-gooey at all. It's a solid core. And a new study from scientists in China says the core has actually slowed its rotation. It's just the latest attempt to describe what's going on at the very center of the planet, a part of the world, it turns out, we don't know a whole lot about. John Vidale teaches Earth sciences at the University of Southern California and has been studying the Earth's core. Professor Vidale, thanks so much for joining us.
JOHN VIDALE: Oh, my pleasure.
RASCOE: I guess to start off with, key to this Chinese study and many of the recent studies of the core is that it spins independently of the Earth's other layers. So how does it do that? And how recently did scientists figure that out?
VIDALE: Well, it happens because the Earth actually is kind of gooey. The core has an inner core that's solid, but it also has an outer core that's basically liquid iron. So there's nothing holding that solid inner core in place. And they noticed back in the 1990s that the inner core was changing over time. And our interpretation is that it's spinning slightly independently of the Earth above it.
RASCOE: What methods do we use to observe it? And how do we know what the core is made of?
VIDALE: Well, we know what it's made of by having a rough idea how the planet formed. You know, it formed very hot back when the solar system first started and melted. And when you take what's out in space and do that to it, the iron kind of sinks to the middle. And then we can sense it by a lot of ways but mainly seismic waves and the gravity field.
RASCOE: Is there debate over, like, whether the Earth's core is moving at all? Or is that mostly settled?
VIDALE: We don't agree about much of anything. We agree it could move. And there's sort of four different trains of thought at the moment. You know, three of them involve the Earth's core rotating various ways, and the fourth thinks it's just changes in the surface of the inner core. You know, for the motion, some people think it swings back and forth every 70 years. Another theory has it wiggling every six years. That's my favorite. There's a third theory that says it had a burst of activity around the year 2000 that lasted a year or two, and it turned half a degree. And the fourth group thinks it's not turning at all.
RASCOE: And you said your favorite is - did you say six years?
VIDALE: Yeah. The idea of a six-year oscillation is that the Earth's core spins a little bit faster for three years and then a little bit slower for three years. And that pattern repeats. And it's because the Earth's inner core is pinned by the gravity of the mantle around it. It moves about a half a degree each way. So that's just five miles or so, a very small oscillation back and forth in a rotational sense.
RASCOE: What would be the benefit, then, of knowing what's going on with the core, since it's so far away from us?
VIDALE: I mean, one idea is that if we understand the Earth's core better - and, you know, we don't understand it very well - we could more knowledgeably figure out the rest of the planets in the solar system and how their cores and magnetic fields work. So that's kind of, you know, fundamental research. And, you know, it is possible there are things we don't know that we should know about.
RASCOE: That's John Vidale, professor of Earth sciences at the University of Southern California. Professor Vidale, thank you so much for joining us today.
VIDALE: My pleasure. Transcript provided by NPR, Copyright NPR.
