What If the Earth Was Hollow? | Unveiled

What if the Earth was Hollow?

Thanks to modern science, we’re pretty sure about what goes on down beneath the surface of Earth. And the cross section of our planet is an instantly recognisable image. But, one particular sci-fi storyline has always fuelled the imagination, too… because what would it be like if, at the centre of our world, there was actually nothing?

This is Unveiled, and today we’re answering the extraordinary question; what if the Earth was hollow?

Although we only ever see its surface, Earth has lots going on under the hood. We live on our planet’s crust, which is split into two types: continental, which is mostly land, and oceanic, which is mostly at the bottom of the sea. Below the crust is the mantle, the biggest of Earth’s various layers and filled to the brim with red hot rock. When this breaks upwards through the surface, as it often does, we get dramatic, volcanic eruptions, and the creation of new crust when it cools. Finally, at the very heart of the planet is the Earth’s core, split outer and inner. We believe the inner core is made of a solid iron-nickel alloy – but we’ve never been down there to check.

We’ve now known for hundreds of years that the Earth is structured like this - made of rock, molten rock and metal all the way through - but notions of a subterranean world have always intrigued people. In Greek mythology, for example, various volcanoes and caves were viewed as entrances to the Underworld. And the “Inferno” section of Dante’s “Divine Comedy” sees Dante descend through Earth into the Christian version of Hell. The centre of the Earth hasn’t always been painted as a land of the dead, though. Some Native American tribes tell stories of life, about their ancestors coming up out of caves to populate the surface. Either way, the mostly inaccessible, underground world has been on our minds for a long time!

But mythology isn’t the same as holding a legitimate belief in a genuinely Hollow Earth. Back in the late seventeenth and early eighteenth centuries, this was something which even top scientists subscribed to - with suggestions that there could be an entire other world beneath us. Perhaps most notably, Hollow Earth Theory was touted by the astronomer Edmond Halley - as in Halley’s Comet. He suggested that there were numerous inner layers to Earth, separated by multiple, distinct atmospheres, before a hot, inner core at the centre (the only part of his idea which still holds up today). Meanwhile, another famous and influential physicist working in the early nineteenth century, Sir John Leslie, reportedly believed that Earth contained two inner suns to illuminate the world below. The Hollow Earth idea was taken to its most extreme and exciting by the science-fiction writer Jules Verne, who penned the 1864 novel “Journey to the Centre of the Earth”, where characters travel to an underground world full of prehistoric flora and fauna. Finally, probably the most bizarre theory of all is the Concave Earth Theory… It alleges that not only is Earth hollow, but that we’re the ones living in the hollow part of it, and that the centre of the universe is the core. Suffice to say, there’s nothing in science to support any of that!

But if the planet really was hollow, would strange creatures and dinosaurs and unique atmospheres all really exist inside it? As a hypothetical, alternate world, it throws up all sorts of possibilities! Burrowing dinosaurs are a relatively recent discovery for palaeontologists, but it’s now thought that some prehistoric creatures may have dug into the Earth’s crust in a bid to escape their extinction sixty-six million years ago. These particular dinosaurs didn’t survive and were killed off with most of the rest of everything else, but if the earth were hollow, then they’d at least have been burrowing to a different place, with a chance of survival. Indeed, if there really was a hidden environment beneath our feet, then by now lots of animals and plants would’ve evolved to access it; to make use of both the surface of this planet, and beneath the surface. Thanks to the probably warmer climate inside of a planet, perhaps there’d finally be a place for the infamous reptilian humanoids of various conspiracy theories, too. Failing that, if the Earth’s hollowness was a recent discovery rather than an always-known-thing, regular humans would no doubt be running shuttle pods to and from this literal Middle Earth, to utilise it as best we can.

Breaking into the centre of the Earth would be no mean feat, though. We know this because of real-world efforts to drill down into the real-world Earth (the one that definitely isn’t hollow). We’ve been drilling into our planet for centuries now, mostly to extract fossil fuels - although, caving (otherwise known as spelunking) is also a recreational pursuit, and humans have travelled to incredibly deep points. The deepest cave discovered so far, the Veryovkina Cave in Georgia, reaches 1.37 miles beneath the surface. That’s more than 7,200 feet down… and it’s still almost a certainty that the Veryovkina Cave is not the deepest cave on Earth. Humans aren’t really built for spelunking, though, unlike the tiny arthropods that live naturally at these depths. We simply can’t squeeze through all the cracks to see how deep a cave truly is. And those 1.37 miles in Georgia are really nothing compared to the actual diameter of the planet, which is more than 7,900 miles through the middle.

That said, the deepest hole humans have ever drilled is significantly deeper than the Veryovkina cave. The Kola Superdeep Borehole in Russia extends more than 7.5 miles down, which is deeper than Challenger Deep at the bottom of the Marianas Trench, the deepest point in the ocean. It took more than twenty years to drill the Kola Borehole, but unlike many of the other “deepest holes on Earth” it’s not an oil well… and was actually created solely as a scientific exercise to drill as deep as possible. To descend to the bottom of it, you would need miles upon miles of rope or cable… only it would still be impossible because the Kola Borehole is only nine inches wide. Clearly then, if Earth actually was hollow, then there’d be no natural passage through to the centre, and we’ve yet to find a way to artificially reach any truly significant depth.

Of course, in reality, there’s no need for us to drill too far… not unless we want to tap magma. In “Journey to the Centre of the Earth”, the characters actually descend through a volcano to get to where they need to go… but suffice to say this wouldn’t quite be possible in the real world. If the Hollow Earth still had a beyond boiling molten mantle, any passage through it would need to be made of a material like solid diamond, with a melting point which might withstand the many thousands of degrees Fahrenheit - with it estimated that the temperature of the Earth’s interior, on the boundary between the mantle and the outer core, is more than 6,500 degrees.

Really, though, if the Earth truly were hollow, there probably wouldn’t be these temperatures to even worry about. The structure of this planet would just be completely different, without magma, or convection currents, or plate tectonics. Without a rotating core to keep everything else going. Rather than a hollow Earth meaning more life in a Jules Verne-style, subterranean second world… it would actually turn this planet into a cold, brittle and uninhabitable wasteland. There’d be no magnetosphere, so no atmosphere, so no life. In fact, unless something else with a huge mass could be found in the middle of it, a hollow planet isn’t really feasible at all… its casing would likely just be crushed by gravity, before reforming into a much smaller, denser body. And the prospects of even the deepest burrowing dinosaurs surviving that are definitely zero.

Exciting as the idea is, it’ll only ever be a science fiction dream and not an everyday reality. Because that’s what would happen if the Earth was actually hollow.