Hawaii is an ideal place to look for rock that might have originated from deep within Earth’s mantle.Credit: M. Patrick/USGS Handout/Anadolu via Getty
Researchers have been challenging the textbook picture of Earth’s structure, which says that what happens in the planet’s dense metallic core stays there. An analysis of rocks from Hawaii’s volcanic islands has found what could be the strongest evidence yet that material is in fact leaking out of the core — and has been pushed all the way to the surface by plumes of hot magma. It was published on 21 May in Nature1.
“This data set will serve as a mainstay as the geochemical community rethinks mantle and Earth history,” says Forrest Horton, a geochemist and petrologist at the Woods Hole Oceanographic Institution in Massachusetts.
Deepest-ever samples of rock from Earth’s mantle unveiled
Previous studies looking at the relative abundances of certain isotopes — versions of the same element with different atomic weights — had hinted that some volcanic rocks contained material from Earth’s core. Some rocks from Baffin Island in Canada have unusually high amounts of helium-3 compared with the more common helium-42, as well as anomalies in ratios of tungsten and hydrogen isotopes3. These signatures could point to material that originated from exchanges occurring around 2,900 kilometres beneath the planet’s surface, at the boundary between the core, which is made mostly of iron and nickel, and the rocky mantle.
But these earlier isotopic hints were “not unambiguous”, says Matthias Willbold, an isotope geochemist at the University of Göttingen in Germany and a co-author of the latest study. “Helium and hydrogen are not specific elements in the core. They could also be part of the mantle.” Looking for more compelling evidence, he and his collaborators focused instead on ruthenium, a rare metal similar to platinum that is known to be concentrated in the core. They measured the relative amounts of ruthenium atoms with atomic weights of 100, 101 and 102 in rock samples from Hawaii. This is an ideal place to look for rock that might have originated from the deepest mantle, says Willbold, because Hawaii’s islands are produced by a ‘hotspot’ where magma thought to originate from the deepest mantle erupts through Earth’s crust.
