Unveiling the colossal subterranean ocean hidden deep within Earth's mantle

Earth service reminds us that scientists have speculated for a long time about the existence of a massive ocean hidden beneath the surface, situated between the upper mantle and lower mantle in the so-called transition zone, at depths from roughly 250 to 405 miles. It also highlights that geophysicist Steve Jacobsen of Northwestern University and seismologist Brandon Schmandt of the University of New Mexico were the first to present direct evidence of such a structure in the scientific journal "Science" in 2014.

Researchers say the vast underground ocean extends beneath the US surface at about 405 miles. They confirmed this using numerous seismographs deployed across the USA in 2000. These devices detected and analyzed seismic waves generated by over 500 earthquakes. As the waves moved deeper into the planet in the so-called transition zone, they accelerated, indicating the presence of a vast water reservoir.

Experts, however, emphasize that the underground ocean is somewhat different in form than its name might suggest. It is neither a liquid nor ice. As explained by the Earth Service, it is instead trapped within the molecular structure of minerals in the Earth's mantle, concealed by a mineral known as ringwoodite, a form of olivine. Ringwoodite, known for its intensely blue colour, contains about 2.5 to 3 per cent water by weight.

This discovery offers a new insight into the Earth's water cycle. It may also significantly impact the theory explaining the presence of water on our planet. It suggests that water comes from asteroids or comets that struck Earth around 4.2 to 3.8 billion years ago during the Great Bombardment. However, Jacobsen's and Schmandt's findings propose instead that water may have originated from within our planet and gradually seeped out from the Earth's core.