The ocean is a big bathtub full of 326 million cubic miles (1.3 billion cubic kilometers) of water, and somebody has unplugged the drain.

Every day, hundreds of millions of gallons of water stream from the bottom of the ocean into Earth’s mantle as part of a very wet recycling program that scientists call the deep water cycle. It works like this: First, water soaked up in the crust and minerals at the bottom of the sea both get shoved into Earth’s interior at the undersea boundaries where tectonic plates collide. Some of that water stays trapped (some studies estimate that two to four oceans’ worth of water are sloshing through the mantle), but large amounts of that water get spewed back to the surface via underwater volcanoes and hydrothermal vents.

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