Nature & Environment
Scientists Uncover Secrets of Earth's Lower Mantle: New Mineral Composition Discovered
Catherine Griffin
First Posted: May 23, 2014 08:41 AM EDT
Our planet consists of multiple layers of solid rock and molten magma, and understanding these layers is crucial to learning more about the processes that shape our Earth. Now, scientists have discovered that the composition of Earth's lower mantle may be significantly different than previously thought, which could help inform future research about how our planet works.
The lower mantle makes up about 55 percent of the planet by volume. Extending from 670 to 2,900 km in depth, it's defined by the so-called transition zone at its top and the core-mantle boundary at its bottom. Massive forces are at work in this layer. In fact, pressures in the lower mantle start at 237,000 times atmospheric pressure and reach 1.3 million times atmospheric pressure at the core-mantle boundary. Any living person would instantly be crushed under such pressure.
In the past, scientists believed that the majority of this lower mantle layer was made up of a single ferromagnesian silicate mineral, commonly called perovskite. Because of its structure, researchers believed that perovskite didn't change much over the enormous range of pressures and temperatures spanning the lower mantle. Yet it turns out that this particular notion may not be true.
Researchers conducted experiments that simulated the conditions of the lower mantle by using laser-heated diamond anvil cells at enormous pressures and temperatures. This revealed that perovskite is, in fact, unstable in the lower mantle.
So what does perovskite look like under these enormous pressure and temperatures? The mineral disassociates into two phases-one a magnesium silicate perovskite, missing iron, and one a new mineral that is iron-rich and hexagonal in structure called the H-phase.
"We still don't fully understand the chemistry of the H-phase," said Li Zhang, the lead author of the new study, in a news release. "But this finding indicates that all geodynamic models need to be reconsidered to take the H-phase into account. And there could be even more unidentified phases down there in the lower mantle as well, waiting to be identified."
The findings could mean some big changes when it comes to creating models of Earth. They could also inform future studies about the processes that work beneath Earth's surface.
The findings are published in the journal Science.
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First Posted: May 23, 2014 08:41 AM EDT
Our planet consists of multiple layers of solid rock and molten magma, and understanding these layers is crucial to learning more about the processes that shape our Earth. Now, scientists have discovered that the composition of Earth's lower mantle may be significantly different than previously thought, which could help inform future research about how our planet works.
The lower mantle makes up about 55 percent of the planet by volume. Extending from 670 to 2,900 km in depth, it's defined by the so-called transition zone at its top and the core-mantle boundary at its bottom. Massive forces are at work in this layer. In fact, pressures in the lower mantle start at 237,000 times atmospheric pressure and reach 1.3 million times atmospheric pressure at the core-mantle boundary. Any living person would instantly be crushed under such pressure.
In the past, scientists believed that the majority of this lower mantle layer was made up of a single ferromagnesian silicate mineral, commonly called perovskite. Because of its structure, researchers believed that perovskite didn't change much over the enormous range of pressures and temperatures spanning the lower mantle. Yet it turns out that this particular notion may not be true.
Researchers conducted experiments that simulated the conditions of the lower mantle by using laser-heated diamond anvil cells at enormous pressures and temperatures. This revealed that perovskite is, in fact, unstable in the lower mantle.
So what does perovskite look like under these enormous pressure and temperatures? The mineral disassociates into two phases-one a magnesium silicate perovskite, missing iron, and one a new mineral that is iron-rich and hexagonal in structure called the H-phase.
"We still don't fully understand the chemistry of the H-phase," said Li Zhang, the lead author of the new study, in a news release. "But this finding indicates that all geodynamic models need to be reconsidered to take the H-phase into account. And there could be even more unidentified phases down there in the lower mantle as well, waiting to be identified."
The findings could mean some big changes when it comes to creating models of Earth. They could also inform future studies about the processes that work beneath Earth's surface.
The findings are published in the journal Science.
See Now: NASA's Juno Spacecraft's Rendezvous With Jupiter's Mammoth Cyclone