Even Jules Verne did not foresee this one. Deep down at the very bottom of the Atlantic Ocean, geochemist Andrea Koschinsky has found something truly extraordinary: "It's water," she says, "but not as we know it."
At over 3 kilometres beneath the surface, sitting atop what could be a huge bubble of magma, it's the hottest water ever found on Earth. The fluid is in a "supercritical" state that has never before been seen in nature.
The fluid spews out of two black smokers called Two Boats and Sisters Peak.
Koschinsky, from Jacobs University in Bremen, Germany, says it is somewhere between a gas and a liquid. She thinks it could offer a first glimpse at how essential minerals and nutrients like gold, copper and iron are leached out of the entrails of the Earth and released into the oceans.
Liquids boil and evaporate as temperature and pressure rise. But push both factors beyond a critical point and something odd happens: the gas and liquid phase merge into one supercritical fluid. For water, this fluid is denser than vapour, but lighter than liquid water.