The highest-resolution map ever showing the fundamental geology beneath Earth’s southern hemisphere reveals something we didn’t know before: an ancient ocean floor that may surround the core .
This thin but dense layer lies about 2,900 kilometers (1,800 miles) below the surface, according to research results published in April. That depth is where the outer core of molten metal meets the rocky mantle above it.this is boundary between core and mantle (CMB).
“Seismic surveys like ours allow us to image the Earth’s internal structure at the highest resolutions, but we are finding that this structure is much more complex than we once thought.” Said When the discovery was announced, Samantha Hansen, a geologist at the University of Alabama, said:
Understanding exactly what lies beneath our feet in as much detail as possible is essential to studying everything from volcanic eruptions to fluctuations in Earth’s magnetic field, which protects us from solar radiation in space.
Hansen and his colleagues used 15 observatories buried in Antarctic ice to map seismic waves from three years of earthquakes. How those waves move and bounce reveals the composition of the Earth’s interior materials. Because sound waves travel slower in these regions, they are called ultra-low velocity zones (ULVZs).
“analyzing [thousands] When we examined the Antarctic seismic record, our high-definition imaging methods discovered thin anomalous zones of CMB material everywhere we investigated. ” Said Edward Garnero, a geophysicist at Arizona State University.
“The thickness of the material varies from a few kilometers to several kilometers. [tens] Kilometers. This suggests that we see mountains in the center, which are five times higher than Mount Everest in some places. “
The researchers say these ULVZs were likely buried under oceanic crust over millions of years.
Although the sunken crust is not close to the subduction zones recognized at the Earth’s surface (zones where rock is pushed down into the Earth’s interior by the movement of tectonic plates), the simulations reported in the study suggest that convection currents could move across the ancient ocean floor. It shows how it was moved to its current resting place. .
It’s hard to infer rock type or movement based on seismic wave motion, but the researchers aren’t ruling out other options. However, at this time, the ocean floor hypothesis appears to be the most likely explanation for these His ULVZs.
There are suggestions that this ancient oceanic crust may have encased the entire core, but it is so thin that it is difficult to know for sure. Future seismic surveys should provide a more complete picture.
One way this discovery will help geologists is to understand how heat from the hotter, denser core escapes into the mantle. The difference in composition between these two layers is greater than the difference between the solid surface rocks and the air above them in our region.
“Our research reveals important connections between the Earth’s shallow and deep structures and the overall processes that move it.” Said Hansen.
This research scientific progress.
A previous version of this article was published in April 2023.