Secrets of inner Earth revealed by tiny diamond

Now one of the world’s premier tourist destinations, Hawaii was a hotspot long before sun-starved travellers began booking all-inclusive Maui vacations.

Over the course of millions of years, molten rock has been spewing out of holes in the middle of the Pacific Plate forming the Hawaiian Island chain.

Scientists attempting to explain the volcanic hotspot phenomenon seen in Hawaii – along with other processes related to plate tectonics – have only been able to hypothesize that it is powered by vast pockets of water deep beneath the surface of the Earth.

But Dr. Graham Pearson at the University of Alberta says he and a team of international researchers have uncovered “solid proof” that confirms the existence of large volumes of water in the area between Earth’s upper and lower mantle known as the transition zone.

The evidence has come in the form of a diamond containing a microscopic sample of a mineral known as ringwoodite. It was brought to the Earth’s surface by volcanic activity and collected in a river in Mato Grosso, Brazil.

Ringwoodite, never before collected from a terrestrial source (it has been observed in meteorite samples), contains a significant amount of water – about 1.5 percent of its weight – and is presumed to be found in large quantities in the transition zone, indicating the presence of immense amounts of water, between about 410 and 660 kilometres, beneath the Earth’s surface.

It’s a discovery that Pearson says is the most important of his career because it may help answer some of the most fundamental questions we have about how the Earth’s inner processes are powered.

“Water is what makes Earth a unique planet in the solar system,” says Pearson, “[It] is probably one of the reasons plate tectonics exists on Earth and doesn’t exist in an ongoing form on other planets.”

Pearson says the confirmation of his hypothesis provided by the ringwoodite sample explains why we see volcanic activity in seemingly unexpected places.

“Classical plate tectonics explain why you get all of these volcanoes around the Ring of Fire… but it doesn’t explain why you get volcanoes in the middle of plates that are well away from subductions zones,” he says.

He adds that hot spots like the one under Hawaii may be powered by increased melting caused by the wet pockets in the transition zone which lower the melting point of the surrounding rock – a process that could only be discussed theoretically before the Pearson team’s discovery of the water-rich ringwoodite sample.

Still Some Proving to Do

Not all scientists familiar with the discovery are so quick to deem the sample of ringwoodite  proof that oceans exist hundreds of kilometers beneath our feet.

Dr. Giorgio Ranalli, an earth science professor at Carleton University, says that while the finding is encouraging, the microscopic size of the ringwoodite sample only allows scientists to make more educated assumptions about the composition of the inner earth.

“Since the depth range between 410 and 660 kilometers is essentially made by [ringwoodite], if all of the ringwoodite in that range contained one percent water, it would be equivalent to an ocean,” Ranalli says, pointing out that Pearson and his team are relying heavily on extrapolation to come to the conclusion that there are substantial water deposits in the transition zone.

The diamond collected by Pearson’s team contains a microscopic sample of ringwoodite – the first ever recovered from a terrestrial source.

But while Ranalli is holding off on dubbing the discovery an impermeable piece of evidence, he is quick to point out why the finding is significant.

“We already knew from x-rays that ringwoodite has the structure that could contain water,” he says of the knowledge that pre-dated Pearson’s discovery.

“Now we know that it does.”

A Call to Governments

Aside from its implications for the way we understand plate tectonics, Pearson hopes his discovery – one which he describes as accidental – will serve a greater purpose in terms of opening government’s eyes to the importance of scientific research, even if there is not obvious end-goal for it in mind.

“Often you find things that you weren’t originally looking for,” Pearson says. “It’s a good example of why politicians should fund blue skies research.”

“It’s how a lot of fundamental breakthroughs occur,” he states.

“It’s not by funding applied research where you think you know what the application is because if you think you know what the application is you’re stifling innovation.”