Earth’s Inner Core Might Be Squishy
Researchers have been aware for a few years that our inner core may not be the simple, solid ball of metal that we believed it to be.
Seismic waves have illuminated that the core doesn’t appear to be truly solid after all, and there are a few competing theories as to why.
In a new study, a team proposes that the inner core is in fact solid, but that the conditions of its location may cause atoms to become hyperactive and make it kind of squishy.
It maybe shouldn’t be so surprising that we discover new facts about the core of our planet fairly frequently. It seems like we really should know pretty much everything about Earth by now, but considering that we can’t get down there first-hand (and even if we could, it’s way too hot and high-pressure), studying our core can be as difficult as studying far-away exoplanets. Anything hard to get at is hard to understand.
But we may have a new tidbit of understanding. Recently, a group of scientists published a study in Proceedings of the National Academy of Sciences claiming that our supposedly solid core is actually kind of squishy. But contrary to what you might think at first, it doesn’t seem to be a composition thing—it’s an atomic thing. Basically, the “solid” stuff our core is made of isn’t actually that solid of a solid.
Here’s the idea. The inner core of our world is mostly made of iron under incredible amounts of heat and pressure. At a molecular level, you can picture iron as a series of individual atoms all held together by bonds in neat, orderly patterns. Usually, that pattern looks like a series of cubes, each with an additional atom at its center. But under the intense conditions at the center of our world, that lattice rearranges itself to instead look like a series of hexagons—kind of like a honeycomb.
While they couldn’t sample the core directly, the researchers wanted to get an up-close look at that interestingly shaped lattice and the conditions that caused it. So, they subjected a piece of iron to a strong and significant impact, replicating the conditions and their effects as best as possible. They input all of the information from that impact into a computer and used an AI to extrapolate it out into a more easily study-able, 30,000-atom “supercell.”
Upon inspecting that “supercell” under the simulated conditions of the Earth’s core, the researchers found that the atoms at the corners of the honeycomb cells were incredibly hyperactive, and would frequently swap places with one another. While this wasn’t enough to shift state or fully destabilize the solid iron, it turns out that it is enough to make the iron kind of squishy.
“Seismologists have found that the center of the Earth, called the inner core, is surprisingly soft, kind of like how butter is soft in your kitchen,” Youjun Zhang, one of the lead authors on the study, said in a press release. “The big discovery that we’ve found is that solid iron becomes surprisingly soft deep inside the Earth because its atoms can move much more than we ever imagined. This increased movement makes the inner core less rigid, weaker against shear forces.”
This all comes as the latest entry in what has become a line of explanations attempting to explain why our core is so inconsistent when we measure it. We study the core of our planet through seismic waves, and whatever those waves tell us is all we have to go on.
In recent years, researchers have become aware that the way that seismic waves are responding to the core is different from how they would respond if it were totally solid. Some researchers have interpreted this as evidence of a separate, solid “inner inner” core, and some have come to believe that the inner core isn’t as solid as we thought at all. But this new squishy-iron idea is a new one altogether.
Only time will tell which theory—or theories—comes out on top. Right now, researchers on the topic are working to confirm initial findings. Maybe someday (and it’s a big maybe) we will be able to truly conquer the elements and directly study what’s down there ourselves. That would give us an answer once and for all.
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