Scientists have drawn the most accurate map of the underlying geology under Earth’s southern hemisphere, revealing something never before discovered: an ancient ocean floor may have curled up around the core.
This thin, dense layer lies about 2,900 kilometers (1,800 miles) below the surface, with a molten metallic outer core and a rocky mantle above it. This is the core mantle boundary (CMB). Understanding exactly what lies beneath our feet – in as much detail as possible – is vital to studying everything from volcanic eruptions to changes in the Earth’s magnetic field, which shields us from solar radiation in space.
“Seismic surveys such as ours provide the highest resolution image of our planet’s internal structure, and we find that this structure is much more complex than previously thought,” says geologist Samantha Hansen of the University of Alabama.
Hansen and her colleagues used 15 monitoring stations buried in Antarctic ice to map seismic waves from earthquakes over a period of three years. The way these waves move and reflect reveals the composition of the materials inside the Earth. Since sound waves propagate more slowly in these areas, they are called ultra-low velocity regions (ULVZ).
“After analyzing (thousands) of seismic records from Antarctica, our high-resolution imaging technique found thin, irregular regions of material in the CMB everywhere we looked,” says geophysicist Edward Garnero of ASU. “The thickness of the material varies from a few kilometers to tens of kilometers. “Kilometers. This indicates that we are seeing mountains at the core, in places reaching five times the height of Everest.”
According to the researchers, this ULVZ is most likely an oceanic crust buried over millions of years.
And while the subducting crust is not near recognized subduction zones on the surface—areas where moving tectonic plates push rocks into the ground—the simulations in the study show how convection currents could have shifted the ancient ocean floor to where it is today.
It is difficult to make assumptions about rock types and their movement based on the movement of seismic waves, and researchers do not rule out other options. However, at the moment, the ocean floor hypothesis seems to be the most plausible explanation for these CLIs.
There is also speculation that this ancient oceanic crust may have wrapped around the entire core, although it is so thin that it is hard to say for sure. Future seismic surveys should complete the overall picture.
One way the discovery could help geologists is by understanding how heat escapes from the hotter, denser core into the mantle. The differences in composition between these two layers are greater than between the hard surface rocks and the air above them in the part where we live.
The study is published in the journal Science Advances.
Source: Science Alert
