Researchers from Northwestern University and the University of New Mexico say they’ve discovered proof of multiple oceans worth of water deep beneath the United States. The researchers say deep pockets of magma located about 400 miles beneath North America are a tell-tale sign of hidden water, although you probably wouldn’t recognize it even if you could see that far underground. Keep reading to find out why.

Northwestern University, underground water, water reservoir, hidden water supply, ancient oceans, hidden oceans, ringwoodite, history of the ocean, Steve Jacobsen

For years scientists have theorized that there is a massive amount of water hiding in the Earth’s mantle–the layer below the crust and above the outer molten core. This new study led by Steve Jacobsen and his colleagues offers the first direct evidence that these theories are correct.

“Using a network of 2,000 seismometers placed across the entire US, they were able to “listen” to the speed of the waves made by earthquakes as they moved through the varying depths of the Earth’s crust,” explains Gizmodo.

Related: The Next California Earthquake Could Be Caused by Human-Made Drought

This technique allowed them to “hear” the difference between water and rock. They discovered a rock called ringwoodite that’s capable of soaking up water like a sponge when subjected to tremendous pressure, and it’s probably a key factor in the creation of magma.

“Geological processes on the Earth’s surface, such as earthquakes or erupting volcanoes, are an expression of what is going on inside the Earth, out of our sight,” said Jacobsen. “I think we are finally seeing evidence for a whole-Earth water cycle, which may help explain the vast amount of liquid water on the surface of our habitable planet. Scientists have been looking for this missing deep water for decades.”

Via Gizmodo, PhysOrg, and Discovery

Water underground via Ringwoodite photo via Steve Jacobsen/Northwestern University