The Earth’s inner core is a ball of iron and nickel about 2,400 kilometers in diameter that is heated to a temperature of 5,200ºC. However, despite its metallic composition, it may not be as hard as previously thought by scientists. A recent study shows that the outer edge of the core has changed shape over the past decades, with some areas rising and falling about 1 kilometer in a few years. It looks like mountains and depressions on the metallic surface of the core.
Core movement
Prof. John Vidale of the University of Southern California, explains, “The outer core most likely affects the inner core, causing it to move.” These findings, published in the journal Nature Geoscience, add new mysteries about the behavior of the Earth’s core.
The inner core is known to rotate at a different speed than the rest of the planet. Some studies show that a few decades ago the nucleus was spinning a little faster, but now it’s spinning slower.
Structure of the Earth
The Earth is made up of several layers. We live on a thin crust, beneath which lies a 2,800 km thick layer of mantle. The mantle is constantly moving, contributing to tectonic processes. The liquid outer core is below, which surrounds the solid inner core, the deepest geologic layer.
Since direct access to the core is impossible, scientists analyze its structure and motion from seismic waves passing through the Earth. They study the speed and direction of these waves, which vary with the density and structure of rocks.
Unexpected discovery
A team of researchers led by Dr. Vidale analyzed earthquakes that occurred near the South Sandwich Islands. A study of 168 “earthquake pairs” between 1991 and 2004 compared seismic signals from Alaska and Canada.
It turned out that the signals were identical in Alaska and different in Canada. This difference indicates changes at the outer boundary of the inner core. This may be the result of turbulent flow in the outer core or the influence of denser parts of the mantle.
The outer boundary of the inner core can deform due to high temperatures close to the melting point, Vidale explains. However, this is not the only possible scenario.
Some scientists, such as Lianxing Wen of Stony Brook University, believe that the change in core shape sufficiently explains the seismic data, and disagree with the idea of a distinct rotation rate of the inner core.
Further research
Geophysicist Hrvoje Tkalčić of the Australian National University notes that the new data supports the idea of a combination of two factors – shape changes and rotational velocity. However, he emphasizes the need to develop seismological infrastructure to obtain more accurate data.
While questions remain open, the results stimulate further research and deepen our understanding of the behavior of the Earth’s core.
Previously, we reported on what would happen after the Earth’s core cooled.
According to science.org
