Jules Verne Was Right: There’s Three Times More Water in Earth’s Depths Than in All the Oceans Combined

In Journey to the Center of the Earth, French writer Jules Verne took us to a lost world beneath our feet, where his protagonists discovered a gigantic inland sea. While the reality is less literal, Verne wasn’t far off the mark. More water lies hundreds of miles below Earth’s surface than in the oceans. However, you can’t sail on it because it’s not liquid.

A rumor about earthquakes. For decades, geologists have wondered why Earth has so much water on its surface. One hypothesis pointed to a “deep water cycle,” a system that traps water inside the planet and slowly releases it.

In 2014, confirmation came when researchers led by geophysicist Steve Jacobsen and seismologist Brandon Schmandt provided the first compelling evidence. Using the USArray—a network of more than 2,000 seismometers spread across the U.S.—the researchers listened to the echoes of earthquakes to map the planet’s interior. They discovered something 410 miles deep.

An underground mineral sponge. Their research revealed huge pockets of magma at depths where they shouldn’t exist. Most molten rock forms much closer to Earth’s surface. The only plausible explanation is a phenomenon known as dehydration melting.

This is where a mineral called ringwoodite comes into play. Intense blue, ringwoodite acts like a sponge, absorbing and retaining enormous amounts of water—not as liquid, ice or vapor, but as a fourth form integrated into its crystalline structure by extremely high pressure and temperatures exceeding 2,012 degrees Fahrenheit.

The Earth’s mantle releases a lot of water. When this “water-soaked” ringwoodite moves into the lower mantle due to tectonic activity, the rock encounters extreme pressure, which causes it to release water. The mineral gets squeezed and releases H₂O. This reaction causes surrounding rock to partially melt. That’s the magma Schmandt and Jacobsen detected.

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How much water are we talking about? The calculations are staggering. If only 1% of the rock’s weight in the transition zone were water, its total volume would be nearly three times greater than all of Earth’s oceans combined—a hidden ocean in the heart of the planet.

The missing proof. While the seismic evidence in 2014 was solid, physical proof was lacking—a direct sample from that wet environment. That proof spectacularly arrived in 2022 inside a diamond mine in Botswana.

Diamonds are time capsules formed under extreme pressure and temperature. Sometimes, they trap tiny fragments of surrounding minerals on their journey to the surface. A team led by gemologist Tingting Gu analyzed this diamond’s imperfections and discovered inclusions of ringwoodite in contact with other minerals, such as ferropericlase and, crucially, hydrated minerals that form in water.

A hydrated underworld. The Botswana diamond confirmed that ringwoodite from Earth’s depths contains water. However, the presence of a variety of hydrated minerals proved this wasn’t a small, localized pocket of water that simply encountered the diamond. There’s a gigantic reservoir of water down there.

Water seeps inward from the surface through the subduction of tectonic plates. It’s stored in minerals such as ringwoodite and eventually released through volcanic activity. This “deep water cycle” influences volcanoes and earthquakes and reveals the ultimate destination of the water Earth swallows. You only had to read Verne to imagine it.

Image | Bhautik Patel (Unsplash)

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