Water – the essence of life, and thankfully abundant on Earth. On the surface, that is. Everyone knows that below the Earth’s crust lies nothing but hot, molten rock. Well, think again. Scientists at Northwestern University and the University of New Mexico have found what could be oceans’ worth of water trapped in Earth’s mantle. The finding significantly alters our view of Earth’s composition.

“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 Northwestern geophysicist Steve 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.”

Of course, there’s a caveat – the water isn’t in the traditional liquid form we’re familiar with. Instead, it’s bound up in rock. The pressure is so great that the water literally splits and gets trapped at the molecular level. Scientists began to suspect the presence of water when they discovered a pocket of magma some 400 miles beneath North America, a finding typically indicates water is also nearby. They believe water gets siphoned below Earth’s crust via plate tectonics.

Though science has long suspected that there was water trapped below the surface, this is the first direct evidence that it exists in this level of the mantle, known as the transition zone. What this means, however, is as yet unknown.

“Whether or not this unique sample is representative of the Earth’s interior composition is not known, however,” Jacobsen said. “Now we have found evidence for extensive melting beneath North America at the same depths corresponding to the dehydration of ringwoodite, which is exactly what has been happening in my experiments.”