One of the recurring tropes of science fiction is the discovery of hidden underground human societies or untouched ecosystems full of bizarre, otherworldly creatures. Now that we have explored nearly every corner of the Earth and have satellites peering down on us from above, deep underground environments represent some of the last frontiers on Earth. While a few recent developments have come close to making the discovery of these hidden mysteries a reality, the technological requirements of getting humans deep into the Earth keep much subterranean exploration just out of our reach. However, a recent study published in the geology journal Lithos has revealed that the Earth might in fact be home to massive underground oceans likely containing unknown forms of life.
According to the published study, a diamond found deep within a Brazilian diamond mine contains a flaw in the form of a specific iron-based mineral that can only be formed through interactions with liquid water:
[...] we report the first direct evidence for water-bearing fluids in the uppermost lower mantle from natural ferropericlase crystal contained within a diamond from São Luíz, Brazil. The ferropericlase exhibits exsolution of magnesioferrite, which places the origin of this assemblage in the uppermost part of the lower mantle.
According to lead researcher Steve Jacobsen of Northwestern University, the presence of the flaw indicates that the Earth likely contains underground oceans as deep as 1000 kilometers (~600 miles) below the surface, which if confirmed could revolutionize our understanding of plate tectonics:
This is the deepest evidence for water recycling on the planet. The big take-home message is that the water cycle on Earth is bigger than we ever thought, extending into the deep mantle. Water clearly has a role in plate tectonics, and we didn’t know before how deep these effects could reach. It has implications for the origin of water on the planet.
Some sources have already speculated that these underground oceans might be home to completely new "alien" forms of life unlike anything we’ve seen on the surface. Earlier this year, one of the deepest water samples ever collected revealed previously unknown types of microbes which can thrive in some of the harshest environments known on Earth.
While discovering new forms of life elsewhere in the universe would be incredible, there are still many untouched places on Earth which are easier to reach and could show us just what life is capable of.