The Mini Museum Library - Articles, Essays, Specimen Deep Dives, and Current Research

The Ocean Below Our Feet

February 28, 2023

The deep mantle diamond (Credit: Tingting Gu)

Early science fiction narratives are replete with journeys to vast underground cave systems, inhabited with creatures from the ancient past who stalk massive caverns or swim in gargantuan subterranean oceans. Today we know the Earth isn’t hollow, but in a twist that sounds like something out of a Jules Verne novel, scientists have discovered evidence for water existing deep below the Earth’s surface, just not in the way you might think.

Tingting Gu, a mineral physicist working under the Gemological Institute of America, has discovered a diamond that contains a ringwoodite inclusion, a type of flaw in the gem. Ringwoodite is a form of magnesium silicate that only forms under the severe pressure levels found below the Earth’s surface, suspended between the upper and lower mantle, over 400 miles underground.

What's incredible is that this mineral also contains water. That means, in order for Ringwoodite to form, the mantle would require the presence of water — concrete evidence towards the idea that there's an ocean locked between layers of rock in our planet.

This discovery has the potential to shed new light on understanding the planet’s volcanic activity and plate tectonics, but it’s also a fascinating discovery and an extremely rare one at that. Only one ringwoodite sample like this has previously been discovered, and it was inadvertently destroyed upon examination.

Ironically, a diamond with an inclusion is less valuable as jewelry given its flaw, but it might just be one of the most valuable diamonds ever in the scientific community.