What If You Fell Through the Centre of the Earth? | Unveiled

What If You Fell Through the Centre of the Earth?

Basophobia is the fear of falling. Most humans and animals have it to at least some degree. But we’re now about to take it to the extreme.

This is Unveiled, and today we’re answering the extraordinary question; what if you fell through the centre of the Earth?

It was Jules Verne who wrote the seminal sci-fi tale, “Journey to the Centre of the Earth”. In that story, the characters travel deep underground to discover a fantastical land crammed with weird, inexplicable creatures and subterranean climate systems. Suffice to say, however, if you really were to journey to the centre of our planet, you wouldn’t really encounter dinosaurs and monsters and underground societies… but that doesn’t mean the trip wouldn’t still be absurdly dangerous.

So, what does science teach us about the centre of our planet? Well, we know that beneath the Earth’s rocky crust and scorching mantle, there’s an outer and inner core. In real life, nobody has gotten even close to this far down, so we don’t have first-hand samples of what the environment is like. But we can very confidently say that it isn’t conducive to human beings hanging around there. The outer core is liquid metal; incredibly hot, and in some parts hotter than even the surface of the sun. The inner core is incredibly hot, too, but also incredibly dense. The pressure is about three-and-a-half million atmospheres down here… and, considering that a human without specialist equipment or vehicles can only withstand about two to four atmospheres, that’s a lot of pressure! The inner core also rotates at a very slightly quicker speed than the rest of the Earth, too… so there’s that to contend with, as well. But, if you were to fall through the centre of the Earth, that’s what you would be passing through.

There isn’t any hole on this planet that you could fall down where this would actually happen, mind you. The deepest hole we’ve ever dug is the Kola Superdeep Borehole, in Russia. It reaches more than 40,000 feet below the ground… but it’s also only nine inches wide. Sure, you could stumble across it and badly twist your ankle, but you’re not about to freefall to the bottom of the Kola Borehole anytime soon. And, even if you could get to the bottom of it, you’d still be a long, long way from the Earth’s centre. In fact, you wouldn’t have even broken out of Earth’s crust, yet. The Kola Borehole is 40,000 feet deep, but the Earth’s crust - its outermost layer - has a depth of about 120,000 feet. To get right to the centre of the Earth - to the middle of the inner core - you’re looking at twenty million feet (or about 4,000 miles).

Say there was an opening deep enough and wide enough to get you there, though… how long would it hypothetically take to go from top to bottom? Much depends on your terminal velocity. Under normal conditions, terminal velocity is when the amount of drag (usually air resistance) and the force exerted by gravity balances out, so that a falling object no longer accelerates; it doesn’t gain any more speed. There are plenty of variables at play here, but we know that skydivers in a flat, stomach-first position can hit a terminal velocity of around 120 miles per hour. We also know that speed skydivers (freefalling in a head-first position) can hit 300 miles per hour. All of which means that, in terms of speed only, if you fell to the centre of the Earth belly-first, and there was comparable air resistance to what there is above Earth’s surface, it would take you about thirty-three hours and twenty minutes to get there. If you fell head-first, it would only take thirteen hours and twenty minutes. In reality, those numbers would be seriously skewed because of changes with gravity… but more on that later!

And, of course, it’s not quite as simple as just digging a hole deep and wide enough and throwing yourself into it, anyway. In practice, you wouldn’t last a fraction of the time it would take you to get to the inner core. Or even to the outer core, or mantle. Heat and pressure are your chief concerns, as well as a lack of oxygen. Currently, standard oxygen tanks run out after about five hours, so you’d certainly need more than one. Carrying them could serve to increase your terminal velocity, thereby getting you there quicker, but even so, let’s assume that you’re doing this at a future time with better technology, and you have more than enough oxygen on you so that you don’t have to worry about it. That leaves only the intense temperatures and crippling pressure.

In general, the temperature steadily rises the further underground you travel and, while it differs from place to place, it can feel noticeably warmer at just a few feet below the surface. The pressure also generally rises, as you travel deeper and deeper (and more and more air is piled on top of you). Again, though, let’s say that you are at least a little bit prepared, and you’re decked out in a futuristic freefall uniform, which somehow keeps you cool and protected enough to survive. What temperatures would it be battling? The Mponeng Gold Mine in South Africa is the deepest working mine in the world, stretching two-and-a-half miles below the ground and requiring a one-hour trip for workers to reach the bottom from the top. And though the tunnels themselves are cooled to more bearable levels, the temperature of the rock at this depth is about sixty degrees Celsius. Hotter than the hottest temperature ever recorded above ground.

Go deeper, and the numbers get crazier. When the Earth’s crust meets the mantle, at between twenty and thirty miles down, temperatures range between two and four hundred degrees Celsius. Midway through the mantle, and we’re now talking nine-hundred miles below the surface of our planet. At the bottom of the mantle, 1,800 miles down and shortly before you transition into the outer core, it’s four thousand degrees. The pressure here is about 1.4 million atmospheres… and although you wouldn’t quite reach that level in a hole filled with air, without an incredibly advanced pressure suit your body will have long since been crushed and crumbled by the incredible mass now above you.

Once inside the outer core, you encounter temperatures exceeding 7,500 degrees, and a magnetic field that’s fifty times stronger than it is at the surface. Move into the inner core, and the temperatures actually drop a little, to a comparatively cool 5,500 degrees… but the pressure mounts up to that three-and-a-half million atmospheres we mentioned earlier, and you still have quite a distance left to travel! The radius of the inner core is just over 750 miles. That’s about 70 percent the radius of the moon… so, if you were still at terminal velocity, you’d still have between two and six hours left to travel. Except, you probably wouldn’t be travelling at that speed anymore, and that’s because of gravity.

Way down in the inner core, gravity doesn’t have quite the effect that it did on the surface. By now, most of the mass of the Earth is actually above you, so the force of gravity feels weaker, which means your terminal velocity will have slowed. For this reason, it’s incredibly difficult to predict just how long it would really take for you to fall through the Earth… but it could possibly take weeks. And, once you finally get to the centre, what then? Would you really just fall through it and out the other side? No… again because of gravity. You might temporarily fall past it, but before long gravity would kick in once more, and pull you back the other way. You’d then be caught in this backwards and forwards motion until you finally came to rest at the very heart of the planet; the innermost region of the inner core, where you’d feel as though you were weightless. It would be an unusual final resting place, to say the least!

In the real world, this isn’t a trip you’re ever likely to embark on. It’s physically unthinkable and practically impossible… so, your basophobia, your fear of falling, needn’t cause you to panic just yet. But, if there was a hole deep and wide enough, and there was a suitable oxygen supply, and an ultra-advanced pressure suit that was also impervious to huge temperature extremes… then it would be a journey we could at least begin to make. Anyone daring enough to venture so far into the dangerous depths of our planet would surely be lauded as a global hero and the ultimate adventurer. But, without also taking with them some kind of means by which to fly their way out the other side, they would also, finally, fall victim to gravity. And that’s what would happen if you fell through the centre of the Earth.