Earth’s many layers are hidden from view. But what if we could drill through the center of the planet to the other side? What extreme forces and temperatures would we encounter deep within the planet?

Even though drilling through Earth remains science fiction, scientists have some ideas about what might occur based on experience from other drilling projects. Earth’s diameter is 12,756 kilometers, so drilling all the way through the planet would require a gargantuan drill and decades of work.

The first layer to drill through is the crust, which is about 100 km thick, according to the U.S. Geological Survey. The atmospheric pressure would increase as the drill traveled farther underground. Every 3 meters of rock is equal to about 1 atmospheric pressure, the pressure at sea level, Doug Wilson, a research geophysicist at the University of California, Santa Barbara, told Live Science. “That adds up really quick when you’re talking about a large number of kilometers,” he said.

The deepest human-made hole today is the Kola Superdeep Borehole in Russia, which is 12.2 km deep. At its bottom, the pressure is 4,000 times that at sea level. It took scientists nearly 20 years to reach this depth, according to World Atlas. And that’s still over 80 km away from the next layer, the mantle, according to Earth layer data from the USGS. The mantle is a 2,800 km layer of dark, dense rock that drives plate tectonics.

The hole made in the quest to drill through the planet would cave in unless we continuously pumped drilling fluid into the hole. In deep-sea and oil-well drilling, that fluid is a mix of mud that includes heavy minerals, like barium. The weight of the fluid balances the pressure inside the hole with the pressure of the surrounding rock and prevents the hole from collapsing, Wilson explained.

Once through the mantle, the drill would finally reach Earth’s core at about 2,896 km down. The outer core is made mostly of liquid iron and nickel and is extremely hot, with temperatures ranging from 4,000 to 5,000 C, according to the California Academy of Sciences. Drilling through this hot, molten iron-nickel alloy would be especially difficult.

“That would cause a whole range of issues,” Damon Teagle, a professor of geochemistry at the University of Southampton in the U.K., told Live Science. The fiery outer core would be like drilling through a liquid, and it would likely melt the drill unless cold water was pumped down.