About 3,000 kilometers (1,864 miles) beneath our feet lies a mysterious collection of material called the D layer, which has long fascinated scientists because of its clumping.
This layer, thin in spots and thick elsewhere, may have formed from an ancient magma ocean that is thought to have covered the early Earth a billion years ago, a new study suggests.
Simulations conducted by an international team of researchers suggest that chemical reactions caused by extreme pressures and temperatures at the bottom of an ancient magma ocean may have caused the unevenness we see in the D layer today.
Their simulations differ from previous models in one key way: water, which was present in Earth’s ancient magma oceans, but whose effect on those oceans as they cooled and solidified is rarely taken into account.
The new study hypothesizes that water can be mixed with minerals to form iron and magnesium peroxide, or (Fe,Mg)O2. This peroxide attracts iron, so its presence could explain how iron-rich layers form where layer D is located. Directly above the boundary between the Earth’s molten outer core and the surrounding mantle.
“Our research suggests that this watery magma ocean favored the formation of an iron-rich phase called iron-magnesium peroxide.” He says Data scientist Qingyang Hu, from the Center for High Pressure Research and Advanced Technology (HPSTAR) in Beijing.
“According to our calculations, its binding to iron could have led to the accumulation of iron peroxide in layers ranging from several to tens of kilometers thick.”
As the iron was withdrawn, these chemical reactions were concentrated in certain areas and the “D” layer was formed, which makes up the team suggests in their new paper.
If their reasoning is correct, it could also help explain ultra-low-velocity zones (ULVZs) found deep within the Earth, dense zones of material that slow seismic waves to a crawl.
Furthermore, the researchers believe that these iron-rich layers had an insulating effect, keeping the different regions down at the base of the layer. Lower sash separate from each other.
“Our findings indicate that iron-rich peroxide, formed from ancient water within the magma ocean, played a crucial role in the formation of the heterogeneous structures of the D layer,” Hu said. He says.
Scientists believe that this magma ocean was created as a result of a massive collision with another planet about 4.5 billion years ago.
Some of the remaining pieces were ejected and formed what we now call the Moon, while a mixture of volatile elements (including carbon, nitrogen, hydrogen and sulfur) remained on our planet to help stimulate life.
Of course, going back that long is not easy, and there is still a lot of scientific debate about what lies beneath the Earth’s surface and how it got there. As we get better at answering these kinds of questions, we’re also getting a better picture of what the Earth was like billions of years ago.
“This model agrees well with recent numerical modeling results, suggesting that lower mantle heterogeneity may be a long-term feature.” He says Geophysicist Ji Ding, of Princeton University.
The research was published in National Science Review.
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