Hundreds of miles below our feet, there is a subterranean mountain range with peaks that may rival the Himalayas, says a new study.
Scientists were able to catch a glimpse of the hulking structures in seismic wave data captured during the 1994 Bolivia earthquake, according to the study, published Thursday in Science.
Earth’s mantle is a dense band of silicate rock that extends from the crust to the core, accounting for 84 percent of our planet’s volume. At 410 miles from the surface, a boundary known as the 660-kilometer discontinuity divides the mantle into its upper and lower levels.
Scientists can tell that rock becomes significantly rougher and denser at this spot, but it’s difficult to get a read of the topography. Detailed information about the boundary could help resolve many mysteries about the mantle, such as how much the upper and lower layers mix together, so scientists wanted to examine it more closely.
One of the only ways to peer inside of Earth is with seismic waves, which are ripples of energy that travel through the planet during major disruptions such as earthquakes or asteroid impacts. When the waves meet different textures, minerals, and structures, they bounce off them in a similar way to light waves reflecting off objects. This provides a rough seismic snapshot of Earth’s interior.
“We need big earthquakes to allow seismic waves to travel through the mantle and core, bounce off the 660-kilometer discontinuity, and travel all the way back through the Earth to be detected at the top of the crust,” Jessica Irving, a geophysicist at Princeton University and an author of the study, told Motherboard in an email.
As the second biggest deep earthquake on record—an 8.2 on the Richter scale—the 1994 Bolivian event fit the bill.
The team enlisted Princeton’s Tiger supercomputer cluster to analyze measurements from the quake, so that they could reconstruct the structures at the boundary.
While the statistical model of the study could not pinpoint exact heights, there is "stronger topography than the Rocky Mountains or the Appalachians” at the boundary, according to lead author Wenbo Wu.
“I can’t give you an estimated number,” Irving said, regarding the range's altitude. “But the mountains on the 660-kilometer boundary could be bigger than Mount Everest.”
The ruggedness of the range may be partly caused by an accumulation of old chunks of seafloor that get sucked into the mantle and then drift down to the boundary. There might be ancient relics of Earth’s earliest days piled up like cairns there.
As seismology and supercomputing techniques continue to develop, scientists hope to learn more about the mantle mountains.
“I think future research will be able teach us more about these topographic mountains and how they are distributed around the planet—we see already that some parts of the 660-kilometer boundary are much smoother than others,” Irving said.
The research not only informs ongoing debates about Earth’s evolution, it also sheds light on the processes and structures that may shape other planets.
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