Studying Earth’s core presents a unique challenge for scientists. Obviously, sending a field team to the core is out of the question, so there’s no hope of getting samples and much of the time, it can be hard to observe changes from the surface, especially given that the crust makes up a mere one percent of the total volume of Earth.
Earth has four main layers. The crust, the thin layer of granite and basalt that encompasses our planet, is where humans, bugs, trees, and all living things are. Next is the thickest layer: the mantle. This is a dense, semi-solid made mostly of iron and magnesium that is slowly circulating under the crust. This layer is also responsible for our seismic activity. Deeper than the mantle is the outer core, which is made from iron and nickel and moves extremely turbulently. This motion generates electrical currents, which is what is responsible for Earth’s magnetic field. Finally, at the inner core of Earth, there is a solid metal ball made of dense iron and nickel that spins very rapidly.
Recent research from the University of Southern California has focused very closely on the outer core. The fact that this layer is responsible for our magnetic field makes it extremely important and also much easier to study since studying the field and seismic activity in the mantle can give us a pretty good idea of what is happening in the core.
Studies have shown that the Earth’s core itself is extremely dynamic. The tumultuous outer core exerts a force on the spinning inner core, which can cause it to change rotation and shape. The inner core also grows slowly over time as the iron in the outer core crystallizes onto it. This suggests that the inner core is being deformed and changed by the outer core.
Using 168 measures of earthquakes taken at Antarctica’s South Sandwich Islands between 1991 and 2024, geophysicists reported in 2023 that the inner core might have been slowing down so much that it may have stopped moving or reversed direction. By measuring how earthquakes move through the Earth, researchers can see how the core deforms the waveform that describes the quake.
According to the research, it is possible that the entire core is deforming. Picture a football being stretched and curved on each end such that the ends point in two new directions. This deformation can also include swelling on the surface and solid ‘bumps’ on the inner core.
The opinions of scientists are not unanimous on this work. Scientists at Stony Brook University argued in 2006 that these changes to the inner core could be temporary and that the inner core melts back into the outer core. Furthermore, Xin Zhang of the University of Science and Technology of China argued that the inner core does not rotate differently than Earth, saying instead that this research could be explained by changes in Earth’s surface.
Future work hopes to illuminate what is actually happening and continue to find more methods to analyze the core of Earth despite being stuck on the surface.
