The Hunt for Earth’s Deep Hidden Oceans

Water-bearing minerals reveal that Earth’s mantle could hold more water than all its oceans. Researchers now ask: Where did it all come from?

A couple hundred pebble-size diamonds, plucked from Brazilian mud, sit inside a safe at Northwestern University. To some, they might be worthless. “They’re battered,” said Steve Jacobsen, a mineralogist at Northwestern. “They look like they’ve been through a washing machine.” Many are dark or yellow, far from the pristine gems of jewelers’ dreams.

Yet, for researchers like Jacobsen, these fragments of crystalline carbon are every bit as precious — not for the diamond itself, but for what is locked inside: specks of minerals forged hundreds of kilometers underground, deep in Earth’s mantle.

These mineral flecks — some too small to see even under a microscope — offer a peek into Earth’s otherwise unreachable interior. In 2014, researchers glimpsed something embedded in these minerals that, if not for its deep origins, would’ve been unremarkable: water.

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