The World Is a Little Off-Center

I’m not going to write about the NIH cuts, devasting though they will be (to researchers, universities, and all of America). I’m not even going to touch on healthcare, or even technology per se, as I usually do. Instead, I want to write about some really cool Science, emphasis on the capital “S.”

Earth’s inner core, it seems, is not always the same shape.

The inner core was previously considered to be solid. (USC Graphic/Edward Sotelo)

Now, in case you forget your high school geology, we live on the Earth’s surface, which rests on the crust, followed by the mantle (which accounts for 84% of the earth), and then, some three thousand miles down, is the core. Think about that carefully: three thousand miles down. By comparison, Mt. Everest is less than 30,000 feet high. The deepest point in the ocean is 36,000 feet down. The deepest hole we’ve ever bored into the earth is 40,000 feet.  Three thousand miles is a looong way down. So, no, we’re never going to get to the core (despite what movies you might have seen). We may get to Mars or even the stars, but not the core.

And it’s big. It’s about 70% of the size of the moon. As one expert put it, “it’s like a planet within a planet.” It is about a third of the Earth’s mass, since it is primarily made of metals (mostly iron and nickel). It’s incredibly hot, close to 10,000 degrees Fahrenheit at its surface, which is about the temperature of the surface of the sun. There’s the inner core, which is basically solid, and the outer core, which is molten. The inner core is only solid, despite the temperature, due to the high pressure it is under.

Now researchers from USC are telling us that the inner core is not quite as solid as we’d thought; it changes shape. John Vidale, Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences and principal investigator of the study, says: “What we ended up discovering is evidence that the near surface of Earth’s inner core undergoes structural change.”

Scientists studying the core had previously found that the core didn’t spin at the same speed or even in the same direction as the rest of the earth, both of which are mind-blowing in themselves. (It’s that spinning, by the way, that generates the magnetic fields which prevents life on earth from being scorched by radiation.) Pretty cool stuff, but the researchers now state: “Previous research has proposed that the inner core has undergone either rotational or shape changes through time, but not both simultaneously.”

If you’re wondering how we can possibly know anything about the core, researchers analyze seismic waves, using them kind of like a form of radar. In this case, USC researchers analyzed what are called “earthquake pairs” – earthquakes that happen in the same place and at about the same magnitude but at different times. “But as I was analyzing multiple decades’ worth of seismograms, one dataset of seismic waves curiously stood out from the rest,” Professor Vidale said. “Later on, I’d realize I was staring at evidence the inner core is not solid.”

“Basically, the wiggles are different,” Dr. Vidale told The New York Times.

“This is kind of the first time we’ve seen the evidence for this kind of motion,” he told The Washington Post. “The surface of the inner core is moving around in ways we hadn’t detected and still don’t understand very well.”

The hypothesis is that, though it may be solid, the edge of the inner core isn’t solid enough to withstand the gravitation pressures from the outer core and the mantle. “Even though that inner core part is really solid, [this boundary] is really soft,” Guanning Pang, a co-author and geophysicist at Cornell University, explained to WaPo. “Maybe as soft as jelly.”

They call these changes “viscous deformation.” Dr. Vidale told Live Science: "We sort of expect that the motion could be on the order of hundreds of meters, maybe a kilometer or two, and we don't know how broad. It could be hundreds of kilometers across."

Wow.

No everyone is convinced. “The offered interpretation is sound,” Hrvoje Tkalcic, a professor of geophysics at the Australian National University who was not involved with the research, told The New York Times, “although it is not the only possible explanation, as the authors acknowledge.” Dr. Vidale acknowledged that the paper is not the final word: “We’re pretty sure we were right, but this isn’t a bulletproof paper. How sure? I sort of put it at 90 percent.”

Bruce Buffett, a geoscientist at the University of California, Berkeley, who was not involved in the work, told Live Science: "Maybe everyone's a little bit right."

That’s how science words; theories are only as good as the next set of facts.

"We'll need to keep accumulating the data and keep searching for the inner core behaviors," Xiaodong Song, a geophysicist at Peking University who coauthored important earlier work on the inner core, told Live Science. "I won't be surprised by future surprises about the inner core behaviors as we keep searching." Dr. Tkalcic believes we should build “seismological infrastructure in remote areas of the planet, including the ocean floor” to help accumulate such data.

In case you’re wondering, the results don’t offer any immediate practical benefits.  The researchers think they may help improve our understanding of Earth’s thermal and magnetic fields, but we’re a long way off from being able to do anything with that understanding. Again, that’s how science works. History suggests that this kind of knowledge will end up being useful someday.

I think it’s great. A part of the Earth that is crucial to our existence yet can’t be directly experienced can be indirectly measured, detecting what are relatively minuscule variations. We still don’t fully understand it, but we understand it better today than we did yesterday.

Gotta love scientists!