Around 1,800 miles beneath your feet lies a giant, blazing-hot ball of metal.
It's the innermost part of our planet, Earth's core. It has a profound impact on your life, though none of us can even glimpse this impossibly remote, hostile place. The core is about the size of Pluto, yet scientists found that distant world in our solar system nearly a century ago, before discovering proof of the core.
"That gives an idea of how remote it is, even though it's right under our feet," James Van Orman, a geochemist at Case Western Reserve University who researches the interior of planets, told Mashable.
Even so, geologists have learned a lot about this potent sphere, which is made of a solid metal inner core surrounded by a liquid metal outer core. But some things remain mysterious, in part because we can't, for many reasons, simply dig an unprecedented tunnel through Earth to get down there. (A geophysicist has proposed an ambitious scheme to send a melon-sized probe into the bowels of Earth, though delivering it to such depths would require manufacturing a strong earthquake with many tons of TNT).
Here's what we know about our core, what we don't, and why it plays a prominent role in all our lives.
Why Earth's core is incredibly hot
Earth's inner core is around 750 miles thick and made mostly of solid iron. (Research published in July 2023 suggests some liquid iron could still be trapped in the inner core, left there during Earth's formation.) It's quite an object. And it's hot.
It reaches some 9,800 degrees Fahrenheit (5,400 degrees Celsius), which is nearly the temperature of the sun's surface.
"It's amazingly hot," emphasized Oliver Tschauner, a research professor at the University of Nevada, Las Vegas, who studies the mineral chemistry of the deep Earth.
"It's amazingly hot."
Since we've never visited the core (in fact, we haven't even gotten through Earth's thinnest layer, the crust), you might wonder how geologists have a confident estimation of what the core is like. They know it's largely iron based on analysis of the behavior and speed of seismic waves from earthquakes that pass through the core. And they've determined the temperature by running experiments on iron and other elements to simulate how such metals behave deep inside Earth, surrounded by intense heat and pressure.
A primary reason the core is profoundly hot is because remnant heat from Earth's formation some 4.5 billion years ago is still there. Long ago, Earth formed inside a disk of hot spinning material that orbited our nascent sun. The chunks of scorching material that bonded together to form Earth contained bounties of heat which, after all this time, still hasn't escaped from the planet's depths. That's because it's extremely well insulated. Above the core is a hot layer of Earth called the mantle; it's a whopping 1,800 miles thick and has the consistency of caramel, keeping the heat in.
"The mantle is basically a thick jacket. It doesn't allow the core to cool very fast," explained Jie Li, a geophysicist at the University of Michigan.
Other factors, too, help keep the core torrid, such as the crystallization of Earth's solid inner core, a long-ago process that also released heat. It's crucial that the core is hot, because these temperatures help create the environment that maintains Earth's vital magnetic field. "Vital" might be an understatement.
How Earth's core sustains a life-protecting magnetic field
Poor Mars.
The Red Planet's once hot core cooled long ago, and without a heated core its magnetic field died, leaving the once water-rich world exposed to the relentless flow of particles from the sun, called the solar wind. The solar wind progressively stripped Mars of its thick atmosphere, leaving it the frigid, callous, irradiated desert we see today. Fortunately for us, Earth's core, as noted above, is hot and vigorous, which sustains our enormously protective magnetic field.
"The magnetic field is crucial for life on Earth," emphasized Li.
"The magnetic field is crucial for life on Earth."
The magnetic field loops out from the poles, trapping harmful solar energy a safe distance away so it can't strip away our atmosphere. This invaluable atmosphere keeps our planet insulated and wet, allowing life to thrive. And the fluid core is responsible for creating this invaluable shield. The outer core, you see, is largely made of molten iron and nickel — an ideal fluid to conduct electricity. As it swirls around and around it acts similar to an electric generator, creating electrical currents that naturally produce a big magnetic field.
Yet the magnetic field holds mysteries we can't yet solve. Earth's hot inner core, once it solidified, generated the immense heat necessary to drive magnetic-creating movement in the outer core. This sustains our magnetic field. But, importantly, geologists don't think this process started until some 3 billion years ago, leaving over a billion years unexplained. "What was driving the magnetic field before that?" Van Orman asked. "We don't know." What's more, there's bounties of proof preserved in rocks that Earth's magnetic field can shift around, and for reasons unknown, even flip.
Fortunately, we're safe. A dynamic magnetic field is normal.
"Earth’s magnetic field and the rotation of the Earth’s inner core are always changing, but scientists have not found strong reasons to believe that changes observed during the last approximately 190 years are a threat to the protective nature of the magnetic field," Mark Abolins, a geoscientist at Middle Tennessee State University, told Mashable. "In addition, scientists know that the Earth’s magnetic field undergoes big changes (reversals) every few hundred thousand years, and life on Earth has continued through numerous reversals during the billions of years that life has been around."
Life finds a way, even when the compass changes.
Can Earth's core stop spinning?
Like Earth, the core rotates. But you may have recently come across some irresponsible media coverage claiming that "Earth's core stopped spinning or rotating," or something similar. But that didn't happen. Not even close.
What did happen, then? Although it's an area of active scientific research, over the last few decades there's been research suggesting that Earth's core has sometimes slightly sped up or slowed down compared to Earth's spin. Recent research published in the major scientific journal Nature Geoscience suggested the core had stopped spinning faster than the Earth as a whole. But it's still spinning, and quite fast.
"It's not like it's going to stop spinning," emphasized Van Orman.
If it did, we'd all notice. And probably get flung into space:
This Tweet is currently unavailable. It might be loading or has been removed.
So, folks, our massive metal core is a pretty wild place. It won't cool down for eons and eons. It's certainly not going to stop spinning. It does change its behavior, for reasons that aren't fully understood. But, then again, don't we all?
This story has been updated with new research about the composition of Earth's inner core.
