Earth's core may be coated in a layer of crystals created by water leaking from the surface: study

• Water leaking into the Earth may be wrapping the core in crystals, a study has suggested.
• The study may help explain a weird area in the outer core that has long puzzled scientists.
• One expert said the theory needs more evidence to be widely accepted. 

Water leaking from the surface of the Earth could be changing the outer rim of our planet's core and wrapping it in a layer of crystals, according to a study.

The experimental research could help crack the mystery of an elusive part of our planet known as the "E-prime layer," an area in the Earth's outer core that has long baffled scientists.

The research could also challenge the idea that the Earth's molten iron core is almost hermetically sealed, study author Dan Shim, a professor of Earth and Space exploration at Arizona State University, said in a press release.

"For years, it has been believed that material exchange between Earth's core and mantle is small. Yet, our recent high-pressure experiments reveal a different story," said Shim.

The finding "points to a far more dynamic core-mantle interaction, suggesting substantial material exchange," he said.

Another expert, however, said more evidence is needed to support this theory.

We still don't know everything about our planet's insides

The Earth's core is only about 1,800 miles under our feet, but it's more inaccessible than Mars.

Intense pressures and high temperatures mean we can't go down there to see what's going on for ourselves.

One way experts peer under our feet is by looking at how seismic waves are deflected by structures inside the Earth. And some of that data doesn't stack up with what we know about our planet.

One of these mysteries is a zone on the outer rim of our Earth's iron core where seismic waves unexpectedly slow down.

The zone, which measures between a few dozen to a few hundred miles in width, has tentatively been suggested to be a layer in its own right and was named E-prime.

Water-logged minerals could spawn crystals around the core's rim

Scientists haven't found a good explanation for that data yet, and that's important — understanding the Earth's core doesn't only help us decipher how our planet was formed and continues to evolve, but it could also shed clues on fluctuations in the Earth's magnetic field.

With their study, published in the peer-reviewed journal Nature Geosciences on November 13, Shim and his colleagues have put forward a new theory to explain the formation of the E-prime layer: that water leaking from the surface can reach the outside of the core and change its chemical composition.

This water wouldn't seep into the Earth as a liquid. Instead, it would be carried by minerals that contain a lot of hydrogen and oxygen inside their chemical structure — these are called "hydrous" minerals.

To support their hypothesis, the scientists simulated the high-pressure conditions of the outer core in the lab. They found that subjecting iron-silica alloys — which are thought to make up the core — to the hydrous mineral in these conditions generates hydrogen-rich and silica-poor elements, which would explain the bizarre seismic data around the E-prime layer.

Meanwhile, the scientists believe the reaction would also spark silicate crystals. These would migrate toward the mantle, creating a dense layer of silica wrapping the core, per the press release.

"We found that when water reaches the core-mantle boundary, it reacts with silicon in the core, forming silica," said Shim in the press release.

The idea is a tall order — scientists tend to think the core gets very little material from the mantle.

If proven to be true, it could also rewrite what we know about how water moves around the insides of the Earth, and would have "profound implications for the geochemical cycles that connect the surface-water cycle with the deep metallic core," the scientists said in the press release.

Jon Wade, Associate Professor of Planetary Materials at Oxford University, told Business Insider in an email the theory "requires further supporting evidence" to garner widespread approval, he said.

There is some evidence that hydrous minerals can be sucked into the Earth — a 2014 study even suggested that there could be a reservoir of water-rich minerals three times bigger than the surface oceans stored about 400 miles under the Earth's crust.

But it's not clear whether that process would bring water all the way to the core, and if it did, whether enough water would make it that far inside the Earth to trigger a reaction on a scale that could explain the E prime layer, said Wade.

"Even if there is a fair amount of water transported to the deep Earth, there are lots of places (3000km of mantle) to 'lose' water to before it makes it the core-mantle boundary," he said. 

"So, could it happen?  Yes, maybe. Does it? Don't know, probably a very minor amount at best," he added.

For him, a "more likely route" would be that hydrogen was encased in the core by a reaction with the core materials, but at the point of the Earth's formation, for instance.

"Other mechanisms may be at play that achieve the same result. It's all kind of speculative but interesting to think about!" he said.

Shim agreed that it's not clear how much water can reach the E-prime layer, but said even a small amount of water could trigger enough chemical reaction to create crystals.

He added that his calculations show that he can explain the E-prime layer "reasonably well" with a range of water transportation scenarios.