"It's very exciting — and might mean we have to re-write the textbooks!"
In school, you probably learned that our planet is made up of four distinct layers: the crust, the mantle, the outer core, and the inner core.
But new research by a team of scientists from The Australian National University (ANU) is shaking up the game: like a Russian doll, they say, the inner core has yet another core hidden inside of it.
This "innermost inner core" may have been caused by a dramatic event early in Earth's history.
"We found evidence that may indicate a change in the structure of iron, which suggests perhaps two separate cooling events in Earth's history," Joanne Stephenson, PhD researcher at ANU, and lead author of a paper about the research published in the Journal of Geophysical Research: Solid Earth, said in a statement.
"The details of this big event are still a bit of a mystery, but we've added another piece of the puzzle when it comes to our knowledge of the Earths' inner core," she added.
The work builds on an older theory.
"The idea of another distinct layer was proposed a couple of decades ago, but the data has been very unclear," Stephenson argued. "We got around this by using a very clever search algorithm to trawl through thousands of the models of the inner core."
Previous research indicates that this innermost inner core appears to take up half the diameter of the overall inner core and has iron crystals pointing in an east-to-west direction, as opposed to the outer, inner core, which has the crystals pointing north-to-south, puzzling scientists.
The new research could have some significant implications.
"It's very exciting — and might mean we have to re-write the textbooks!" Stephenson said.
READ MORE: Scientists dig deep to reveal Earth’s hidden layer [ANU]
More on the Earth's core: The Earth's Core Is Leaking, Baffling Scientists