Professor’s gem leads to an underground ocean of discovery

A University of Alberta professor’s research into a mineral found in a worthless brown diamond sparked an ocean of interest from the scientific community last March, and it has now helped prove a long-standing theory about the existence of water beneath the Earth.

Scientists have long wondered about the amount of water that lies beneath the Earth, and U of A Canada Excellence Research Chair Graham Pearson’s discovery of the first sample of the mineral ringwoodite within an unassuming gem offered a missing piece of the puzzle. Now, in a study released June 13 in Science magazine, scientists have confirmed the existence of a massive water reservoir 7,000 kilometres beneath the Earth’s surface containing three times the volume of the oceans.

Study co-author Steven Jacobsen, from Northwestern University in Illinois, said Pearson’s discovery that ringwoodite is composed of 1.5 per cent water was a “message in a bottle” for researchers. It proved water exists 400 to 700 kilometres below the Earth’s surface.

“Many people in the (scientific) community assumed there would be water down there, but this is based largely upon laboratory experiments,” Jacobsen said. “But what has been missing is real observational data from seismology. Real evidence in the real Earth that what we do in the lab actually happens in the Earth.”

Pearson’s diamond offered some of that “real evidence” researchers needed. The diamond containing the ringwoodite was discovered by luck in 2008, when Pearson and his team were doing research in Brazil. The ringwoodite, a compressed form of the common mineral peridot, had been trapped in the gem for millions of years.

Pearson’s study, alongside laboratory research, helped Jacobsen and his peers confirm that the water found inside the ringwoodite is also found much farther down inside the Earth’s mantle, or the layer of rock between the planet’s surface and core. In using 2,000 seismometers to study waves caused by earthquakes as well as studying dehydration melting — a type of rock melting that happens within the Earth at lower pressure — scientists learned that water slows at the Earth’s mantle.

“What it’s telling us is that the water cycle actually extends deeper, much deeper, into the Earth than we thought before,” Jacobsen said.

Some researchers believe water accumulated when comets struck the Earth, but this study suggests ocean water could have risen from the Earth’s mantle — offering a new theory on where our oceans’ water came from, and on the complexity of the Earth’s water cycle.

It’s a big discovery stemming from a dull diamond worth only $10, but offers an invaluable glimpse into the Earth’s composition.