Picture a vast cavern, hundreds of miles inside the Earth, where an immense subterranean ocean laps at shores that have never seen the light of day. OR, picture a whole bunch of rock that looks pretty much like rock, but incorporates about 1-2% water within its crystalline structure. Those are two different visions of recent research suggesting the presence of a surprising amount of water in the transition zone between the upper and lower mantles of the Earth’s innards.
The latter vision is the one held by the groups of research scientists involved, building on a convergence of evidence from seismic soundings and geochemical analysis of a rare mineral called ringwoodite, a minute sample of which (of deep terrestrial rather than the usual meteoric origin) was recently recovered in Brazil. Their conclusions converge in turn on research published in 2007 on the Beijing Anomaly, a huge zone of water-rich rock underlying parts of Asia, locking in roughly the equivalent of the Arctic Ocean. The research is, er, groundbreaking, with exciting implications for the finer understanding of plate tectonics and the terrestrial water cycle. But the reporting of it has led to some predictable misunderstandings.
The popular-science press articles on the research speak of subterranean “oceans” – note the quote marks, plus clear statements within the body of the text that “ocean” is not meant to be taken literally. Nevertheless, certain quarters of the pseudoscientific fringe have promptly transformed these into oceans, sans the quote marks: real, rolling oceans, with lots of room for other speculations as well. Headline: Evidence Proves There’s an Ocean Deep Inside the Earth, Maybe Life. Headline: Hollow Earth Evidence? Massive Ocean Discovered Inside Our Planet. Yes, just as the creationists adopted the Beijing Anomaly as Noah’s “fountains of the deep”, the Hollow Earth bunch have adopted this research as copper-bottomed evidence for their particular passion.
The Hollow Earth is a peculiar inversion of the alien hypothesis—instead of outer space, it postulates an inner space, the Earth as a hollow 
shell with us on the outer surface, somebody else on the inner surface, and usually a teeny sun hanging in the centre. Of course, the concept of an underworld is an old and honourable one in folklore and myth, from origin narratives involving ancestors emerging from caves to dwell under the sun, to various ideas about the afterlife and the abodes of supernatural beings. In the 19th century, however, the Hollow Earth Hypothesis took on a quasi-scientific veneer, while also spawning a whole genre of science fiction. Indeed, it is often hard to distinguish between the avowed fiction and the “facts” that Hollow Earth aficionados regard as gospel truth, and the two have clearly cross-pollinated each other from the beginning. In the 20th century and to the present, an element of conspiracy theory was added: the authorities know perfectly well the Earth is both hollow and inhabited, but as usual are hiding the facts from the public.
Visions of what lies and/or lives inside the Hollow Earth are strikingly diverse, everything from lost-world survivals of dinosaurs and cavemen, up to hyper-advanced civilizations with aircraft in the form of airborne crockery—flying saucers, that is. In fact, there is an entertaining overlap between Hollow Earthers and other patches of the lunatic fringe, incorporating references to Atlantis, UFOs, and the lost super-civilization. Theosophy and its siblings place some of their Ascended Masters in the subterranean world, in which case it would seem more proper to call them Descended Masters. Hitler is supposed to have sent an expedition to the Antarctic to search for one of the polar gateways, though spoilsport historians think he only wanted a whaling station. Admiral Byrd is supposed to have overflown the entrance at the north pole and observed wondrous things, though he was inconveniently in Antarctica at the time. To the tragicomic Richard Shaver, the inhabitants of the underworld were the Dero—short for Detrimental Robots, though they were some form of flesh and blood—cannibalistic, sadistic, and prone to kidnapping and torturing humans from the world above, notably himself.
At any rate, true believers in the Hollow Earth, like the Creationists, appear quick to seize on scientific evidence that can somehow be misconstrued into support for their claims. In this case, the word ocean was all it took.
