Heavy iron isotopes escape from Earth’s core

Earth’s molten core may leak iron, according to researchers who analyzed how iron behaves inside our planet.

The boundary between the liquid iron core and the rocky mantle lies about 2,900 miles (2,900 km) below Earth’s surface. In this transition, the temperature drops more than a thousand degrees from the hottest core to the coldest mantle.

The new study suggests that the heavier iron isotopes migrate to lower temperatures, and to the mantle, while the lighter iron isotopes circulate back to the nucleus. (Isotopes of the same element have different numbers of neutrons, giving them slightly different masses.) This effect could cause the core material infiltrating the lower mantle to become enriched for heavy iron isotopes.

“If correct, this will improve our understanding of the core-mantle interaction,” said Charles Lesher, lead author, professor emeritus of geology at UC Davis and professor of earth system petrology at Aarhus University in Denmark.

Understanding the physical processes operating at the core-mantle boundary is important for interpreting seismic images of the deep mantle, as well as for modeling the extent of chemical and thermal transfer between deep Earth and our planet’s surface, Lesher said.

Lesher and colleagues analyzed how iron isotopes move between areas of different temperatures during experiments conducted at high temperature and pressure. Their findings may explain why there are more heavy isotopes of iron in mantle rocks than in chondrite meteorites, the primary material in the early solar system, Lesher said.

“If true, the results suggest that the core iron has been leaking into the mantle for billions of years,” he said.

Computer simulations carried out by the research team show that this core material can even come to the surface, mixed and carried by hot rising mantle feathers. Some lavas erupted at oceanic hot spots like Samoa and Hawaii are enriched with heavy iron isotopes, which Lesher and the team propose could be the signature of a leaking core.

The study was published April 6 in the journal. Nature Geoscience.