We know people have wanted to journey to the center of the Earth since at least 1864 when Jules Verne published Journey to the Center of the Earth. Likely it was a curiosity for at least a few years before that. But the practicality of digging your way to the planet’s center is not as easy as you might think. We went to the moon, but we haven’t gone to the Earth’s core, and that’s kind of impressive.
It’s 3,959 miles to the center of the Earth, though that obviously varies a bit depending on your starting point. It’s 3,963 miles at the equator and 3,949 miles at the north pole. Thank the rotation of the earth making it not exactly a perfect sphere for the variation.
As a concept, it’s not difficult to wrap your head around the idea of digging a hole to the center of the Earth. In modern times you can imagine that we might use a giant drilling machine. But digging mine shafts is a remarkably old human innovation. The ancient Egyptians were mining gold as far back as 4,000 years ago.
The Egyptians pioneered shaft-sinking technology. Later cultures like the Greeks, the Persians, and the Romans all borrowed these techniques from the Egyptians for their own mining. It was horribly unsafe work and mostly was forced upon criminals because nobody cared if they died in the process. It was only years later, when forced labor was harder to come by, that safety conditions improved.
Simpler mines are much, much older than what the Egyptians made. The oldest known mine dates back to 43,000 BC in Africa. Suffice it to say that humans have been digging holes in search of stuff for a very long time.
Despite the amount of time we have spent digging holes, digging exceptionally deep holes is a very different thing. The deeper you dig, the more dangerous it gets. There are a lot of reasons why digging to the center of the Earth is not something you can do by just taking a shovel into the yard. But modern technology is pretty amazing. So if someone wanted you right now, could they get to the center of the earth? And how close have we gotten already? Let’s take a look.
What’s in the Center?
The center of the Earth is a sphere of mostly iron that has a radius of 758 miles. It’s over 5,000 degrees Celsius and under immense pressure, which we’ll touch on later. Despite the fact the core is incredibly hot, it’s not liquid. Though iron melts at about 1,500 degrees C, the pressure in the center of the earth keeps it solid.
The core is under so much pressure and is crushed so densely that the atoms of iron cannot freely move about in a liquid state despite the temperature. Instead, they simply switch places back and forth with neighboring atoms in a very tight-knit little dance.
Some research suggests the core is not a solid or even plasma but a superionic substance that exists in a state between liquid and solid.
The various layers of the Earth, from the inner core to the outer core, to the mantle and crust, have been determined not through drilling but through seismology. The study of earthquakes has allowed scientists to determine what lies below us. We can analyze seismic waves and determine how they travel similar to watching light waves or listening to sound waves. They’ve been likened to using X-rays to see internal body structures. The study lets us know how much of the earth’s interior is solid, how much is liquid, how dense it must be, and so on.
As this technology improves we’ve come to learn that the interior of the earth is far more complex than those four basic layers we’ve all been taught about. The mantle, for instance, has numerous transitions within it. There are even mountain ranges in the mantle, with peaks that nearly dwarf Everest.
The Deepest We’ve Gone
As of 2024, the deepest humans have ever been able to drill into the Earth was at the Kola Superdeep Borehole. Drilled into the Kola Peninsula in the Russian Arctic, this hole blew away anything else we have attempted before. The project was started by the Soviet Union in 1970 and continued all the way to 1992.
The Kola Superdeep Borehole goes an astounding 40,230 feet into the earth. That works out to about 7.6 miles. Or 0.19% of the way to the center. That’s the best we’ve ever done.
You may have read about the Al Shaheen oil rig being deeper but it’s actually not. The oil rig hole extends 40,318 feet, but it’s not down, so Kola is still deeper. By a considerable margin, in fact. The Sakhalin well in Russia is similar, reaching a length of 40,604 feet but not straight down like Kola.
Part of the reason Kola was abandoned in 1992 was that the drilling team was dealing with temperatures around 180 Celsius or 356 Fahrenheit. They were expecting close to a hundred degrees cooler than that. At another hole in Germany, this one just 30,000 feet deep, the temperatures reached 500 F.
Other projects have been conducted elsewhere around the world. The US dug a gas well in Oklahoma that reached six miles before it ran into molten sulfur and had to shut down. Project Mohole in the 1960s tried to drill from beneath the ocean but ran out of money.
Is it Possible?
Sorry to bury the lede on this one, but essentially the answer is no. We can’t go to the center of the Earth. There are many issues when engaging in seriously deep drilling. One, which we already touched on, is heat. The deeper you go, the hotter it gets.
Drilling equipment is built to handle the heat from friction, but if you have friction heat plus what you’re drilling is already up to 350 F or hotter, then you’re making the problem worse. Drilling equipment starts to break or melt. Especially when temperatures rise more than expected. Also, the rock has to deal with the heat. If the friction and pressure start to melt the rock, it becomes goopy and harder to drill into. This doesn’t even count for the outer core of the Earth which actually is molten iron and nickel.
The center of the Earth is believed to be about 5,200 C or 9,300 F. If drills can’t manage to get down to a fraction of the depth without the heat disabling them, nothing we have created so far could ever withstand drilling to that depth and temperature.
As concerning as heat on par with the surface of the sun is pressure. Pressure at the center of the earth would be 3.5 million times what we experience on the surface. Again, no functional tool we have ever developed could hope to survive drilling into something like that. The buildup of this pressure also contributes to the holes collapsing on themselves and needs to constantly be balanced by pumping in fluid to balance it as well as temperatures.
Instability plagued both the German KTB borehole and Kola. Ideally, the drill needs to be perfectly vertical to reduce torque, but this is incredibly hard to do. The deeper the drills go, the more unstable they can become and the more likely they are to break. Kola got stuck in a rock and couldn’t proceed any deeper which is what stopped the drill from continuing.
By the time the KTB borehole was finished, the team had to pull back and start again several times after difficulty maintaining the borehole caused it to break down. Equipment broke and could not be retrieved so the drill had to be pulled back enough to try drilling down again. They ended up using a 6.5” drill bit when they could finally drill no more.
Both KTB and Kola also suffered funding losses. These were multi-million dollar projects. Kola had the unfortunate issue of being a Soviet project, meaning the end of the Soviet Union put a real monkey in that wrench. But KTB also could not secure funding to continue the work, it’s just too cost-prohibitive.
The German government had spent $338 million by the time it was done. Kola was believed to have cost about $100 million. Adjust for inflation that’s about $253 million today.
One last concern is time. It took 15 years to drill the KTB borehole. It took 22 years to drill Kola. If Kola could continue at the same pace all the way to the center it would take just shy of 11,000 years.
What Would Theoretically Happen?
Okay, so we just stomped all over the idea of getting to the center of the earth. But we’re not really drilling down there, we’re just talking about it, right? So what would happen if you could get there in theory?
Obviously, you’re going to have to deal with the things we’ve already discussed that have stopped progress so far – incredible heat and incredible pressure. But let’s pretend we have a nice, wide, stable hole all the way to the center. Jump in!
At about one kilometer, or 0.6 miles deep in this hole, the temperature will be over 45 C or 113 F, so you’re going to start suffering heat stroke. It’s only going to get worse from here and you’re 0.02% of the way there. You’ll hit boiling temperatures before two miles deep, so you’re going to want to bring a fan or some bottled water to stay cool.
At 30 miles deep you’d run into a magma problem. Yes, you’re already dead from the heat, but now you’re going to be totally reduced to soot. But let’s ignore that and keep going.
On the more fun side of things, if you can travel in a vacuum, after free-falling for a while you’d be hitting speeds of nearly 17,400 miles per hour. So it’s going to be a short trip! If you’re not in a vacuum, then you’re stuck at terminal velocity and, by the time you hit the center, gravity would even out and you’d be trapped in that sphere of 5,000-degree iron.
At 3.6 million atmospheres of pressure, you can’t really exist anymore. Free divers can train themselves to handle 10 atmospheres of pressure in the water, but they do run the risk of permanent injury or death. Some people have managed to get to 30 atmospheres.
The Titan submersible which famously suffered a tragic accident and imploded on the way to the wreckage of the Titanic experienced up to 400 atmospheres. Needless to say, 3.6 million is almost impossible to comprehend.
If you’re in a hole or tube and it has air in it, all the air above you is pushing down creating air pressure unlike anything on the surface. Within 50 kilometers or 30 miles, you’d reach air pressure equal to the ocean floor.
Another issue is that you’re traveling faster than the hole you’re falling down. The earth is spinning, and that means the walls of your tunnel are going to smack into you until you are beaten to a pulp. Man, this hole can’t stop killing you, can it?
So, really, no matter how theoretical you get with it there’s no easy way to escape the myriad of horribly painful things that would happen to you if you tried to go to the center of the Earth. Maybe it’s a good thing we can’t get there. Unless, of course, laser drilling proves feasible someday.