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Our perspective of Earth tends to be very shallow–literally.
Everything we experience, from the deepest depths of the ocean to the
highest mountain peaks, only skims the top of the outermost layer of the
Earth, the crust, which is about 4 miles thick under the ocean and 20
to 30 miles thick on land. With a radius of 3,959 miles, the Earth has
plenty of secrets buried inside it.
But today it has one less secret. Researchers have just published a paper in Nature Geoscience
announcing they’ve discovered a remarkably stiff layer in the Earth’s
mantle–the layer of molten or pliable rock located between the crust
and the Earth’s core. The new layer floats somewhere around the middle
of the mantle.
“The Earth has many layers, like an onion,” Lowell Miyagi, a geologist at the University of Utah, said in a press release.
“Most layers are defined by the minerals that are present. This layer
isn’t defined by the minerals present, but by the strength of these
minerals.”
In this case, the researchers knew from previous studies that tectonic plates
(which hold the oceans and continents) sometimes slide under each other
and get pushed down into the mantle. Those slabs of rock tend to stop
moving temporarily at around 930 miles below the Earth’s surface, but no
one could figure out why.
Observing the process directly was out of the
question–because for one, no one has ever drilled down to the mantle,
and secondly, the process of a slab sliding down into the mantle takes
around 300 million years. So Miyagi and his team did the next best
thing.
They used an instrument called a diamond anvil (made from,
yes, diamonds) to apply massive amounts of pressure to rocks commonly
found in the mantle. When they got to pressures that mimicked conditions
at that 930 mile depth, they found that the strength in the rocks had
increased by an insane amount–it was nearly 300 times stronger than
that same type of rock would be at levels higher in the mantle. Below
that 930 mile point, atoms within the rocks start to move more freely,
loosening up, and allowing the slabs to sink.
But because the
rocks at the 930 mile boundary are so strong and stiff, slabs of the
tectonic plates stall out for a while, caught between a rock and a stiff
place.
Credit: Popular Science
