Remnants of Earth’s crust survive in the planet’s interior

Slab unperturbed in the mantle for billions of years before resurfacing

Earth’s crust is the ultimate survivor. Bits of crust that sink into the planet’s interior can last for billions of years, geologists report in the April 25 Nature.

ROCKY REMAINS Volcanic rocks in the Cook Islands have revealed that Earth’s crust can survive in the mantle for billions of years, as evidenced by sulfur isotopes trapped within crystals of the mineral olivine (blue, in this light-filtered image). James M.D. Day

Rita Cabral of Boston University and colleagues discovered traces of ancient crust in one of the South Pacific’s Cook Islands while analyzing lava that erupted 20 million years ago. The rock contains different forms, or isotopes, of sulfur in ratios that could have only originated in an atmosphere with little oxygen, sometime before 2.45 billion years ago.

The researchers suspect that the sulfur was originally part of a slab of oceanic crust that slid beneath another tectonic plate and plunged into the mantle more than 2.45 billion years ago. The crust sank so low in the mantle that it was effectively in a crustal graveyard, the team suggests, where convection was weak and the crust could stay intact. A couple billion years later, parts of that crust rose back to the surface in a plume of buoyant mantle material and fueled the volcanic eruptions that gave rise to the Cook Islands.

Erin Wayman is the managing editor for print and longform content at Science News. She has a master’s degree in biological anthropology from the University of California, Davis and a master’s degree in science writing from Johns Hopkins University.

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