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Researchers have unearthed the elusive 'sixth ocean' on Earth, yet it doesn't lie on the planet's surface.
While there are traditionally recognized as five oceans on Earth—the Atlantic, Pacific, Indian, Arctic, and Southern Oceans—a consortium of international scientists has uncovered substantial evidence of a significant water reservoir between the upper and lower mantle layers of the Earth.
According to an international study, scientists have uncovered a reservoir containing water with a volume three times larger than all the oceans on Earth combined. However, instead of existing on the planet's surface, this water has been found within the transition zone between the upper and lower mantle layers of the Earth.
WHERE IS THE 'SIXTH OCEAN'?
Evidence suggests that water resides in the transition zone (TZ), the boundary separating the Earth's upper and lower mantle layers. This zone extends from 410 to 660 kilometers deep, where immense pressure, reaching up to 23,000 bars, causes olivine minerals to undergo a structural transformation, turning olive-green in color.
Research has confirmed what was long theorized, that ocean water accompanies rock slabs and thus enters the transition zone. This means our planet's water cycle encompasses the interior of the Earth.
Professor Frank Brenker from the Geological Sciences Institute at Goethe University in Frankfurt, Germany, explains: 'These mineral transformations greatly impede rock movement within the mantle. For instance, mantle plumes—upwellings of abnormally hot rock within the mantle—sometimes halt just below the transition zone. The movement of material in the opposite direction is also stalled. Subducting slabs (a crucial component of subduction zones) often struggle to break through the entire transition region. Hence, there's even a graveyard of such slabs in this region beneath Europe'.
However, the long-term effects of 'sucking' material into the transition zone on its geochemical composition and whether a larger water volume exists there remain unknown.
Professor Brenker elaborates: 'Subducting slabs also carry deep-sea sediments into the Earth's interior. These sediments can harbor significant amounts of water and large CO2 reservoirs. Yet, it's still unclear how much goes into a more stable form within the transition zone, such as hydrated minerals and carbonates—and thus whether a large water volume is actually stored there'.
Current conditions certainly favor that. Dense minerals like wadsleyite and ringwoodite can (unlike olivine at shallower depths) store large amounts of water—indeed, to the extent that theoretically the transition zone could absorb six times the water volume in all our oceans combined.
'So, we know the transition zone (TZ) has the potential to store a very large amount of water. However, we don't know whether it actually does so or not' - Professor Brenker stated.
A DISTINCT OCEAN WITHIN THE EARTH
Evidence of the 'sixth ocean' was found during the analysis of a rare precious diamond formed 660 km beneath the Earth's surface.
Following the study of a rare diamond found in Botswana, Africa—formed at a depth of 660 km, amidst the transition zone (TZ) and the Earth's lower mantle, where ringwoodite is prevalent—scientists discovered a significant amount of impure ringwoodite, high in water content, encrusting the diamond.
Diamonds from this region are exceedingly rare, even among ultra-deep-sourced rare diamonds, comprising only 1% of diamonds. Furthermore, the research team has been able to identify the chemical composition of the rare diamond. It closely resembles every shard of mantle rock found within basaltic rock anywhere in the world. This indicates the diamond undoubtedly originates from the Earth's mantle.
'The impurities within the 1.5 cm diamond were large enough to allow for precise chemical composition determination. In this study, we've demonstrated that the transition zone is not a dry oceanic slab but harbors a significant amount of water. This also brings us closer to the idea of French writer Jules Verne's [author of the famous works 'Journey to the Center of the Earth' (1864), 'Twenty Thousand Leagues Under the Sea' (1870)] concept of an ocean within the Earth. The difference being there's no liquid water ocean beneath, but rather water-logged rock' - Professor Brenker shared.
The research team explains that the high water content of the transition zone has profound implications for the dynamics within the Earth and if ruptured, it could lead to large-scale mass movements in the mantle.
A study by a German-Italian-American research group, published in the journal Nature, states that the internal structure and dynamics of the Earth are shaped by the 660 km boundary between the transition zone of the upper and lower mantle.
Source: NDTV, IndiaToday
