[Rockhounds] Continents of the Underworld Come Into Focus

[Kreigh Tomaszewski]

ecades ago, scientists first harnessed the echoes of earthquakes to make a
map of Earth’s deep interior. They didn’t just find the onion layers you
might remember from a grade school textbook — core and mantle covered by a
cracked crust. Instead, they saw the vague outlines of two vast anomalies,
unknown forms staring back from the abyss.

Over the years, better maps kept showing the same bloblike features. One
huddles under Africa; the other is beneath the Pacific. They lurk where the
planet’s molten iron core meets its rocky mantle, floating like
mega-continents in the underworld. Their highest points may measure over
100 times the height of Everest. And if you somehow brought them to the
surface, God forbid, they contain enough material to cover the entire globe
in a lava lake roughly 100 kilometers deep.

“It would be like having an object in the sky, and asking, ‘Is that the
moon?’ And people are like, no. ‘Is that the sun?’ No. ‘What is it?’ We
don’t know!” said Vedran Lekić <https://www.geol.umd.edu/vedranlekic>, a
seismologist at the University of Maryland. “And whatever it is, it is
intimately tied to the evolution of the Earth.”

The first mystery of these hulking, hidden seismic features is whether
they’re made of different stuff than the rest of the Earth’s mantle. The
second: How do these patterns in the deep leave traces on our surface world?

Neither case is settled. But in recent years, many earth scientists have
begun to make the case that these vague shapes are piles of dense,
smoldering rock that date to the dawn of the planet. And multiple studies
in the past year have argued that their persistent influence might be
responsible for long-puzzling patterns in volcanic hot spots like Hawaii.

https://www.quantamagazine.org/continents-of-the-underworld-come-into-focus-20200107/