Scientists recently discovered a massive reservoir of water, buried around 700 kilometers beneath the Earth’s surface. This hidden water could hold three times the amount of all the oceans combined. However, it’s trapped in deep mantle rocks and can’t be seen or accessed directly.
This finding suggests that some of Earth’s water may originate from inside the planet rather than just from comets or asteroids. This could explain why ocean levels have remained stable over millions of years, despite shifting continents and changing climates.
Understanding how water behaves deep in the mantle sheds light on Earth’s geology and the long-lasting oceans we have today.
The water is trapped in a rare mineral known as ringwoodite. This mineral absorbs water at the molecular level, acting like a sponge under the immense pressure in the mantle’s transition zone, which lies between 410 and 660 kilometers deep. Steven Jacobsen of Northwestern University, who led the research, explained that the team utilized about 2,000 seismographs across the U.S. to analyze seismic waves from over 500 earthquakes. They found that these waves travel slower in wet rock, revealing where water is stored. Jacobsen likened their technique to using earthquakes as a “planetary MRI.”
“We should be grateful for this deep reservoir,” Jacobsen remarked. “If it wasn’t there, the Earth would be mostly underwater, with only mountain tops emerging.”
This discovery also transforms our understanding of the water cycle. Water from the oceans sinks into the mantle at subduction zones, where minerals like ringwoodite absorb it. Over time, some of this water returns to the surface through volcanic activity, helping keep our oceans stable.
This deep water system is far larger than what we see in clouds and rivers. Jacobsen noted that it explains why liquid water has persisted on Earth for billions of years, unlike planets like Mars and the Moon, which have lost theirs.
Looking ahead, scientists aim to study other regions worldwide to see if water-rich ringwoodite is common or limited to specific areas. They also want to refine their understanding of how much water the transition zone holds and how quickly it cycles between the surface and the mantle. Recent research indicates that about 70% of Earth’s interior water may cycle over millions of years, playing a crucial role in plate tectonics and ocean stability.
Though this water is unreachable, its existence provides crucial insights into why our oceans have been stable for so long, allowing life to thrive on our planet.
For further reading on Earth’s water cycle and geology, check out this article from Science.
