Earth’s inner core solidified sometime after 565 million years ago — just in time to not only save the planet’s protective magnetic field from imminent collapse, but also to kick-start it into its current, powerful phase, a new study suggests.
The finding, reported online January 28 in Nature Geoscience, supports an idea previously proposed by simulations that Earth’s inner core is relatively young. It also provides insight into how, and how quickly, Earth has been losing heat since its formation 4.54 billion years ago —key to understanding not only the generation of the planet’s magnetic shield but also convection within the mantle and plate tectonics.
“We don’t have many real benchmarks for the thermal history of our planet,” says Peter Olson, a geophysicist at Johns Hopkins University who was not involved in the new study. “We know the interior was hotter than today, because all planets lose heat. But we don’t know what the average temperature was a billion years ago, compared with today.” Pinning down when iron in the inner core began to crystallize could offer a window into how hot the interior of the planet was at the time, Olson says.
The planet’s iron-nickel core is made up of two layers: a solid inner core and a molten outer core. When that solid inner core formed is a long-standing mystery (SN: 9/19/15, p. 18). “Proposed ages have been anywhere from 500 million years ago to older than 2.5 billion years,” says coauthor John Tarduno, a geophysicist at the University of Rochester in New York.