The Earth’s inner core is incredibly tricky to study, since it’s buried beneath thousands of miles of rock. New seismic studies suggest that it’s not just a solid ball of iron, as has been assumed, but might have pockets of liquid iron throughout.
Like flakes settling at the bottom of a snow globe, iron and other heavy metals tend to sink through the lighter molten rock and so end up concentrated at Earth’s core. But exactly what form the iron takes when it gets there remains up for debate. For a long time it was assumed to be liquid, due to the extremely high temperatures it faces there.
But in the 1930s scientists began to probe the core by studying seismic waves from earthquakes. Watching how these reflect back to sensors, it’s possible to get a sense of what types of material they’re moving through at different stages. These studies revealed that the inner core was a solid ball of iron.
However, it may not have the same consistency all the way through, according to a new study from the University of Utah. The team used data gathered by the International Monitoring System (IMS), a network of sensors set up around the world originally to detect illegal underground nuclear explosions. They analyzed seismic waves from 2,455 earthquakes of magnitude 5.7 and up, and used them to map the inner core’s internal structure in more detail.
The scattering pattern that they picked up revealed that the core isn’t the same all the way through. It is largely solid, but seems to contain what the researchers describe as a tapestry of different “fabrics,” a product of its growth over time.
“We think that this fabric is related to how fast the inner core was growing,” said Keith Koper, overseer of the study. “A long time ago the inner core grew really fast. It reached an equilibrium, and then it started to grow much more slowly. Not all of the iron became solid, so some liquid iron could be trapped inside.”
Other studies have found that the inner core might be solid but squishy, or made of a strange superionic alloy that exists in a state of matter partway between a liquid and solid. Gaining a better understanding of what’s going on down there can help us learn more about the history of our planet, how the protective magnetic field formed and is maintained, and could inform how we figure out if other planets are habitable.
The new research was published in the journal Nature.
Source: University of Utah
