New research guides us towards the fact that the Earth’s core might be leaking. Previous schools of thought deemed that every action occurring in the dense core stayed there. An analysis of rocks from Hawaii’s volcanic islands gives the strongest evidence yet regarding the leakage of material from the core to the surface of the Earth via plumes of hot magma. Samples have been recovered that passed across the boundary between the planet’s core and its mantle, nearly 3,000 kilometres below the surface.
Previous studies investigated the relative abundance of certain isotopes (same elements with different atomic weights). These studies hinted at the presence of materials from the Earth’s core. For example, some rocks collected from Baffin Island in Canada have unusually high amounts of helium-3 compared with the more common helium-4. Anomalies in ratios of tungsten and hydrogen isotopes were also noted. These signatures showed that some exchange of materials was occurring at 2,900 kilometers beneath the Earth’s surface, at the boundary of the mantle and the core.
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. According to him, helium and hydrogen are not specific elements in the core, and can also be a part of the mantle. In his hunt for more compelling evidence, he and his co-workers focused on a rare metal like platinum, called ruthenium. The team measured the relative presence of ruthenium atoms of the atomic weights 100, 101, and 102 in the rock samples collected from Hawaii. Hawaiian rocks are one of the best samples, as the volcanic islands of Hawaii are produced by a ‘hotspot’— a place where magma from the deepest areas of the mantle has erupted through the Earth’s crust.
Willbold’s co-author, Göttingen geochemist Nils Messling, had to work on the technique for extracting tiny traces of ruthenium from rock samples to get good data. Then, the rock samples were passed through a mass spectrometer. “The expected differences were so small that previous analyses would not be able to pick up that signal,” Willbold says. The team discovered that the ruthenium isotope signatures differed from those elsewhere on Earth.
Given the geological history of our planet, the core formed more than four billion years ago. In contrast, much of the material in the mantle and crust came from later meteor bombardments. This indicates these different regions have distinct isotopic concentrations. The differences in the materials present in the core, and the mantle and the crust also reflect the same.
According to Willbold, these results also prove that the magma carrying material to the surface must come from the mantle-core boundary. Forrest Horton, a geochemist and petrologist at the Woods Hole Oceanographic Institution in Massachusetts, says that the data will be a mainstay as the results revolutionize what we think of the mantle and Earth’s overall history. He believes the evidence is compelling, but it is too early to rule out alternative schools of thought. Studying rock samples from other ‘hotspots’ can provide further evidence and information.
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