The high water content of the transition zone has far-reaching consequences (Representational Image)
Scientists have discovered a water reservoir three times the volume of all oceans below the Earth’s surface, according to an international study. Water was found between the transition zone of the Earth’s upper and lower mantle. Using techniques such as Raman spectroscopy and FTIR spectrometry, the research team analyzed a ratio diamond that formed 660 meters below the Earth’s surface, ANI reported.
The study has long confirmed that this is just a theory, namely that ocean water accompanies the subducting plates and thus enters the transition zone. This means that our planet’s water cycle includes the interior of the Earth.
“These mineral transformations greatly inhibit rock movements in the mantle,” explains Prof. Frank Brenker of the Geosciences Institute at Goethe University in Frankfurt. For example, mantle plumes—columns of hot rock rising from the deep mantle—sometimes stand directly below the transition zone. The movement of the mass in the opposite direction also comes to a standstill.
“End slabs often have a hard time breaking through the entire transition zone. So there’s a whole cemetery of such slabs in this region under Europe,” Brenker says.
However, until now it was unknown what the long-term effects of material “absorption” into the transition zone were on its geochemical composition and whether there was larger amounts of water there. Brenker explains: “Emitting plates also carry deep-sea sediments into the Earth’s interior. These sediments can hold large amounts of water and CO2. But until now it was unclear how much of it entered the transition zone in the more stable form aqueous minerals and carbonates — and therefore , it was also unclear whether large quantities of water were actually stored there.”
Current conditions will certainly be favorable to this. The dense minerals wadsleyite and ringwoodite (unlike olivine at lesser depths) can store large amounts of water—in fact, so large that the transition zone could theoretically absorb six times the amount of water in our oceans. “So we knew that the boundary layer has an enormous capacity to store water,” says Brenker. “However, we didn’t know if that was really the case.”
An international study involving a Frankfurt geoscientist has now provided the answer. The research team analyzed a diamond from Botswana, Africa. It was formed at a depth of 660 kilometers, at the interface between the transition zone and the lower mantle, where ringwoodite is the dominant mineral. Diamonds in this region are very rare, even among the super-deep origin rare diamonds, which make up only one percent of diamonds. Analyzes revealed that the stone contains numerous ringwoodite inclusions that exhibit high water content. Also, the research group was able to determine the chemical composition of the stone. It was nearly identical to that of almost any mantle rock found in basalts anywhere in the world. This showed that the diamond definitely came from a normal piece of Earth’s mantle. “In this study, we showed that the transition zone is not a dry sponge, but retains a significant amount of water,” says Brenker. “This also brings us one step closer to Jules Verne’s idea of an ocean inside the Earth.” The difference is that there is no ocean below, but watery rock that doesn’t feel wet or drip, according to Brenker.
