Excerpted from Volcanoes Are Hot: Oliver’s Great Big Universe #2 by Jorge Cham. September 2024. Published with permission by Amulet Books, an imprint of ABRAMS.
Earth is a lot like a boba tea drink.
You know those boba tea drinks they sell in some shops where they shake it, but when they give it to you all the different things in it have floated to a different spot in the cup? The ice floats to the top, then the bits of fruit float under that, and the boba balls all fall to the bottom?
Well, the same thing happened to Earth. Back when it was a big ball of lava billions of years ago, all the different things in it floated to a different level. The lighter rocks floated to the top, the heavier rocks floated just below that, and all the metal stuff sank to the bottom.
Earth is round, sort of, so when the heavy stuff sank, it went to the center of Earth, and when the lighter stuff floated, it went to the outer part of Earth.
That makes the inside of Earth look like what happens when you cut an avocado or a hard-boiled egg in half, and you can see all the layers.
I told my aunt someone should make an avocado and egg boba tea drink, and she said that definitely wouldn’t help my bathroom situation.
My aunt says if you tried to dig a hole to the other side of Earth, this is what would happen: First, you’d dig through loose stuff, like dirt or sand. It might be a little, or it might be as much as a whole football field of it (about 0.1 kilometers).
Then you’d hit the first layer of rock.
The dirt and the layer of rock are called the crust. That’s because it’s . . . crusty. It’s mostly made of rock that’s extra brittle, or crumbly. It’s 5 to 70 kilometers thick, which sounds like a lot, but it’s pretty thin compared to the whole Earth. It’s about as thick as an eggshell is to its egg.
Then the second layer you have to dig through is called the mantle. This one is made of heavier rocks, and it’s pretty thick. You’d have to dig through 2,800 kilometers to get through it.
The mantle is where lava comes from. That’s where it gets formed as magma, before it shoots up through the cracks in the crust. If you’re ever digging through the mantle, you better hope you don’t accidentally dig into some magma.
Then after the mantle is Earth’s core. This is a big ball in the middle of the planet that’s mostly made of a metal called iron. The first 2,200 kilometers of it is called the outer core, and it’s oozy and melted, which means you can’t dig through it. And in the center is a solid metal ball called the inner core, which is 2,450 kilometers wide.
So if you tried to dig to the other side of the world, it would take you a long time, you might hit some magma, and you’d have to swim through liquid metal and cut through solid iron.
Not only that, my aunt said it’s SUPER HOT inside Earth. It’s still kind of hot from when Earth was a big ball of lava, AND there’s a lot of radioactive stuff inside Earth, which heats up the rock and metal.
The surface of Earth is nice and cool because we’re close to space, which is really cold. But inside the mantle, the temperature is 3,500°C, and the core is 6,000°C. That’s pretty hot if you think about the fact that the surface of the sun is also about 6,000°C.
There’s also a lot of pressure inside Earth. That’s from all the rock and metal trying to squish together because of gravity’s pull. If you were to dig down that deep, you’d get squished into a pulp pretty quick.
Speaking of pressure, I still had to go to the bathroom.
Jorge Cham is the bestselling, Emmy Award–nominated creator of . . . many things: from the hit PBS show Elinor Wonders Why to the hit nonfiction book for adults called We Have No Idea, along with the hit podcast Daniel & Jorge Explain the Universe and the popular webcomic PHD Comics. He is, without a doubt, an expert on explaining things about the world in interesting and fun ways. He obtained his PhD in robotics from Stanford University and was an instructor and research associate at Caltech from 2003 to 2005. He is originally from Panama.