For centuries, humans believed Earth's oceans were confined to the surface—until now. A groundbreaking discovery has revealed a hidden ocean, buried deep within the Earth's mantle, 700 kilometres below the surface. The question haunting scientists today: Could this reservoir, three times larger than all of Earth's surface oceans combined, redefine our understanding of the planet's water cycle?
The massive ocean, however, isn’t what you might expect. No waves crash here, no fish swim. Instead, this 'ocean' is trapped in the crystal structure of a rare blue rock called ringwoodite. This rock, found in the Earth’s mantle, holds vast amounts of water—not in liquid form, but in a crystalline lock. The implications of this discovery are staggering: could Earth’s water have been hiding beneath our feet all along?
The research team, led by Steven Jacobsen from Northwestern University, used innovative techniques to uncover this mystery. More than 2,000 seismographs stationed across the U.S. were deployed to track seismic waves generated by over 500 earthquakes. The scientists noticed that waves slowed down significantly at certain depths, signalling the presence of water-rich rocks. These seismic techniques allowed them to “see” below the Earth's surface in ways never before imagined.
By measuring the velocity of seismic waves at different depths, the team inferred the presence of water trapped in the mantle. This seismic "X-ray" of the Earth led to the astonishing realisation that a hidden ocean has been lurking below, waiting to be discovered.
The discovery also raises profound questions about the origins of Earth’s water. Until now, the prevailing theory suggested that water arrived via comet impacts. However, this new finding suggests that water may have seeped from Earth's interior over millions of years. It flips the traditional narrative upside down, presenting a new view of Earth’s deep-water cycle.
This hidden reservoir may be the key to understanding the long-term stability of Earth’s surface oceans. Scientists now speculate that this underground ocean could play a critical role in cycling water between Earth’s interior and its surface. More research is planned, with global studies aiming to uncover if similar water-rich pockets exist in other regions. The potential global implications could change how we view water distribution on our planet.
