Article Posted on : - Mar 15, 2014

Earth's molten core. A NASA/JPL image

PARIS (AFP): A hundred and fifty years ago, in "Journey to the Centre of the Earth", French science-fiction forerunner Jules Verne pictured a vast sea that lay deep under our planet's surface.

Today, that strange and haunting image has found an unexpected echo in a scientific paper.

Writing in the journal Nature, scientists said they had found an elusive mineral pointing to the existence of a vast reservoir deep in Earth's mantle, 400-600 kilometres beneath our feet.

It may hold as much water as all the planet's oceans combined, they believe.

The evidence comes from a water-loving mineral called ringwoodite that came from the so-called transition zone sandwiched between the upper and lower layers of Earth's mantle, they said.

Analysis shows that a whopping 1.5 per cent of the rock comprises molecules of water.

The find backs once-contested theories that the transition zone, or at least significant parts of it, is water-rich, the investigators said.

"This sample really provides extremely strong confirmation that there are local wet spots deep in the Earth in this area," said Graham Pearson of Canada's University of Alberta, who led the research.

"That particular zone in the Earth, the transition zone, might have as much water as all the world's oceans put together."

Ringwoodite is named after Australian geologist Ted Ringwood, who theorised that a special mineral was bound to be created in the transition zone because of the ultra-high pressures and temperatures there.

A piece of this mineral has been a long-sought goal. It would resolve a long-running debate about whether the poorly-understood transition zone is bone-dry or water-rich.

But, until now, ringwoodite has only ever been found in meteorites. Geologists had simply been unable to delve deep enough to find any sample on Earth.