Earth may have formed with oceans in its interior

WASHINGTON: Earth may have formed with oceans in its interior and has been continuously supplying water to the surface via plate tectonics, a new study suggests.

The study also indicates that the same amount of water that currently fills the Pacific Ocean could be buried deep inside the planet right now.

The study by The Ohio State University may help answer a longstanding question: Did our planet make its own water through geologic processes, or did water come to us via icy comets from the far reaches of the solar system?

The answer is likely "both," the researchers said. At the American Geophysical Union (AGU) meeting in Washington, DC, yesterday, researchers reported the discovery of a previously unknown geochemical pathway by which the Earth can sequester water in its interior for billions of years and still release small amounts to the surface via plate tectonics, feeding our oceans from within.

Wendy Panero, associate professor of earth sciences at Ohio State, and doctoral student Jeff Pigott pursued the hypothesis that Earth was formed with entire oceans of water in its interior, and has been continuously supplying water to the surface via plate tectonics ever since.

Central to the study is the idea that rocks that appear dry to the human eye can contain water in the form of hydrogen atoms trapped inside natural voids and crystal defects.

Oxygen is plentiful in minerals, so when a mineral contains some hydrogen, certain chemical reactions can free the hydrogen to bond with the oxygen and make water.

Stray atoms of hydrogen could make up only a tiny fraction of mantle rock. Given that the mantle is more than 80 per cent of the planet's total volume, however, those stray atoms add up to a lot of potential water.

In a lab at Ohio State, the researchers compress different minerals that are common to the mantle and subject them to high pressures and temperatures using a diamond anvil cell - a device that squeezes a tiny sample of material between two diamonds and heats it with a laser - to simulate conditions in the deep Earth.

They examine how the minerals' crystal structures change as they are compressed, and use that information to gauge the minerals' relative capacities for storing hydrogen.

Then, they extend their experimental results using computer calculations to uncover the geochemical processes that would enable these minerals to rise through the mantle to the surface - a necessary condition for water to escape into the oceans.

A recent research found that ringwoodite, a form of olivine, contains enough hydrogen to make it a good candidate for deep-earth water storage.

So Panero and Pigott focused their study on the depth where ringwoodite is found - a place 523-804 km below the surface that researchers call the 'transition zone' -- as the most likely region that can hold a planet's worth of water.

From there, the same convection of mantle rock that produces plate tectonics could carry the water to the surface.