December 1, 2023


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The Earth’s core seems to be wrapped in an unexpected ancient structure: ScienceAlert

The Earth’s core seems to be wrapped in an unexpected ancient structure: ScienceAlert

The most accurate map yet of the underlying geology beneath Earth’s southern hemisphere reveals something we didn’t know before: an ancient ocean floor that may have wrapped around the core.

This thin but dense layer exists about 2,900 kilometers (1,800 miles) below the surface, according to a study published in April. This depth is where the molten metallic outer core meets the rocky mantle above it. This is the The basic boundary of the mantle (CMB).

“Seismic investigations such as ours provide the highest resolution depiction of the internal structure of our planet, and we have found that this structure is vastly more complex than we previously thought.” He said geologist Samantha Hansen of the University of Alabama when the results were announced.

Understanding exactly what’s under our feet — in as much detail as possible — is vital to studying everything from volcanic eruptions to changes in Earth’s magnetic field, which protects us from solar radiation in space.

Seismic waves generated by earthquakes in the Southern Hemisphere have been used to sample ULVZ structure along Earth’s core-mantle boundary. (Edward Garnero and Mingming Li/Arizona State University)

Hansen and her colleagues used 15 monitoring stations buried in the Antarctic ice to map the seismic waves caused by the earthquakes over a three-year period. The way these waves move and bounce off reveals the composition of the matter inside the Earth. Because sound waves move slower in these regions, they are called ultra-low velocity regions (ULVZs).

“analysis [thousands] From seismic recordings from Antarctica, our high-resolution imaging method found thin, anomalous regions of material in the CMB everywhere we examined. He said Geophysicist Edward Garnero of Arizona State University.

The thickness of the material ranges from a few kilometres [tens] of kilometres. This indicates that we see mountains in the heart of the Earth, which in some places are five times higher than Mount Everest.”

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According to the researchers, these ULVZs are most likely oceanic crust buried over millions of years.

While the sinking crust is nowhere near the recognized subduction zones at the surface — the areas where moving tectonic plates push rock down into the Earth’s interior — the simulations featured in the study show how convection currents could have moved the ancient ocean floor back to where it rested. Present. .

convection mantle
Rock movements in the mantle. (Hansen et al., Science advances2023)

It’s difficult to make assumptions about rock types and their motion based on seismic wave motion, and researchers aren’t ruling out other options. However, the ocean floor hypothesis seems to be the most likely explanation for these ULVZs at the moment.

There’s also a suggestion that this ancient ocean crust could have wrapped around the entire core, although it’s so thin it’s hard to know for sure. Future seismic surveys should be able to add more to the overall picture.

One way this discovery could help geologists is by learning how heat escapes from the hotter, denser core into the mantle. And the differences in composition between these two layers are greater than they are between the solid surface rocks and the air above them in the part on which we live.

“Our research provides important connections between shallow and deep Earth structure and the overall processes that drive our planet.” He said Hansen.

The research has been published in Science advances.

A previous version of this article was published in April 2023.