Chunk of seafloor lost during age of dinosaurs found hiding under Pacific

A piece of seafloor that began sinking into Earth's mantle approximately 250 million years ago has been discovered, at least its fingerprints have. Scientists say they have found a "fossilised fingerprint" of the chunk of seafloor hiding under the Pacific Ocean.

A study has found that the fingerprint matches a slab of Earth's crust that started going down at the beginning of the age of dinosaurs (252 million to 66 million years ago).

It was once a part of the seafloor in the southeastern Pacific. Experts are hoping to solve the mystery of a strange gap in the lowermost sections of the mantle by learning more about the latest discovery.

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The findings were published on Sep 27 in the journal Science Advances.

"It's giving us a glimpse into Earth's past that we've never had before," Jingchuan Wang, study lead author, a seismologist and postdoctoral associate at the University of Maryland, said in a statement.

The slab currently sits between the upper and lower mantle, in the mantle transition zone stretching between 410 to 660 kilometres deep beneath the Earth's surface. This zone expands and contracts owing to heat currents, researchers said in the statement.

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Exploration happened near Easter Island

The discovery was made when the researchers were exploring the mantle beneath the East Pacific Rise. This region is a mid-ocean ridge located 3,200 km off the coast of South America.

Seismic waves were used to examine the types of rock beneath the seafloor, after which a digital cross-section of Earth's crust and mantle was created. They noticed an unusually thick mantle transition zone beneath a portion of the East Pacific Rise around 350 km east of Easter Island. "This thickened area is like a fossilised fingerprint of an ancient piece of seafloor that subducted into the Earth," Wang said.

Subduction occurs after a collision between two tectonic plates, after which one dives beneath the other. The resulting material usually disintegrates in the mantle and turns into magma owing to high temperatures. However, the researchers say the newly discovered slab somehow escaped that fate.

"Usually, oceanic slabs of material are consumed by the Earth completely," Wang said.

A subducting plate would travel a lot faster through the mantle than what happened with this piece of slab, according to the statement. Wang said that this suggests the mantle transition zone can act as a viscous barrier and slow the movement of sinking material.

"This is just the beginning," Wang said. "We believe that there are many more ancient structures waiting to be discovered in Earth's deep interior."