[Rockhounds] Geochemists solve mystery of Earth's vanishing crust

[Kreigh Tomaszewski]

Thank goodness for the Earth's crust: It is, after all, that solid,
outermost layer of our planet that supports everything above it.

But much of what happens below that layer remains a mystery, including the
fate of sections of crust that vanish back into the Earth. Now, a team of
geochemists based at the Florida State University-headquartered National
High Magnetic Field Laboratory has uncovered key clues about where those
rocks have been hiding.

The researchers provided fresh evidence that, while most of the Earth's
crust is relatively new, a small percentage is actually made up of ancient
chunks that had sunk long ago back into the mantle
<https://phys.org/tags/mantle/> then later resurfaced. They also found,
based on the amount of that "recycled" crust, that the planet has been
churning out crust consistently since its formation 4.5 billion years ago—a
picture that contradicts prevailing theories.

https://phys.org/news/2020-06-geochemists-mystery-earth-crust.html