The Earth’s history is embedded within the layers of the ground beneath our feet. While we generally consider this fact to be common knowledge, recent research has uncovered little-known chapters within the Earth’s past, particularly in its inner core.
For years, geophysicists have been taught that the Earth consists of four main layers: the crust, the mantle, the outer core, and the inner core. However, a few years ago, Australian National University geophysicist Joanne Stephenson and her colleagues discovered evidence that suggests the inner core may actually have two distinct layers. This finding challenges the traditional understanding of Earth’s structure and may require revisions to existing textbooks.
“It’s very exciting – and might mean we have to re-write the textbooks!” Stephenson explained at the time.
To support their claim, the team used a search algorithm to compare thousands of models of the inner core with observed data about how seismic waves travel through the Earth. The team discovered that the inner core’s anisotropy, or the differences in the make-up of its material, can affect the properties of seismic waves. Some models suggest that the material of the inner core channels seismic waves faster parallel to the equator, while others indicate that the mix of materials allows for faster waves more parallel to Earth’s rotational axis.
The study did not reveal much variation with depth in the inner core, but it did find evidence of a change in the slow direction to a 54-degree angle, with the faster direction of waves running parallel to the axis. According to Stephenson, this may indicate a change in the structure of iron, which suggests two separate cooling events in Earth’s history. These new findings may also explain why some experimental evidence has been inconsistent with our current models of Earth’s structure.
While the team’s conclusions align with other studies on the anisotropy of the innermost inner core, the researchers acknowledge that their conclusions are limited by the distribution of global earthquakes and receivers. Further research may fill in the missing data gaps and allow scientists to corroborate or contradict their findings. Regardless, these new findings shed light on another chapter in Earth’s history and add another piece to the puzzle of our knowledge of the Earth’s inner core.
This research was published in the Journal of Geophysical Research.
READ MORE: Earth Has Just Started Emitting Giant Magnetic Waves From its Core (Video)