Earth’s molten core may be leaking heavy isotopes of iron, according to a study led by geoscientists from Aarhus University and the University of California, Davis.
Heavier iron isotopes migrate toward lower temperatures into the mantle, while lighter iron isotopes circulate back down into the core. Image credit: L. O’Dwyer Brown, Aarhus University.
The boundary between the liquid iron core and the rocky mantle is located some 2,900 km (1,800 miles) below Earth’s surface.
At this transition, the temperature drops by more than a thousand degrees from the hotter core to the cooler mantle.
The new study suggests heavier iron isotopes migrate toward lower temperatures — and into the mantle — while lighter iron isotopes circulate back down into the core.
This effect could cause core material infiltrating the lowermost mantle to be enriched in heavy iron isotopes.
“If correct, this stands to improve our understanding of core-mantle interaction,” said Professor Charles Lesher from the University of California, Davis and Aarhus University.
“Understanding the physical processes operating at the core-mantle boundary is important for interpreting seismic images of the deep mantle, as well as modeling the extent of chemical and thermal transfer between the deep Earth and surface of our planet.”
Professor Lesher and colleagues analyzed how iron isotopes move between areas of different temperatures during experiments conducted under high temperature and pressure.
“Our findings can explain why there are more heavy iron isotopes in mantle rocks than in chondrite meteorites, the primordial material from the early Solar System,” Professor Lesher said.
“If true, the results suggest iron from the core has been leaking into the mantle for billions of years.”
Computer simulations performed by Professor Lesher and co-authors show this core material can even reach the surface, mixed with and transported by hot, upwelling mantle plumes.
Some lavas erupted at oceanic hot spots such as Samoa and Hawaii are enriched in heavy iron isotopes, which the team proposes could be a signature of a leaky core.
The team’s paper was published in the journal Nature Geoscience.
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C.E. Lesher et al. Iron isotope fractionation at the core–mantle boundary by thermodiffusion. Nat. Geosci, published online April 6, 2020; doi: 10.1038/s41561-020-0560-y
