Earth's Core is Slowing Down, But Don't Worry!

A visualization of the Earth's magnetic field, generated by the iron inner core. (Source: NASA)

3,200 miles below our feet, a massive ball of iron lies at the heart of our planet, and it's starting to slow down. The Earth’s inner core is about as hot as the surface of our sun, but it’s this fiery iron sphere that sustains life on our planet by generating the magnetic field that protects us from solar winds. So when you hear that the Earth’s core has been slowing down, you might be inclined to panic, but never fear! The core is simply going through a process it’s repeated an untold number of times before.

First things first, how do we even study the Earth’s core? Scientists rely on seismic readings to record how earthquake waves are distorted as they travel through the Earth. When seismologists began using this method, they found that concurrent waves from earthquake doublets were being distorted differently. This must have meant the Earth’s core was spinning, and thus in different positions as the successive waves passed through.

Notes taken by Igne Lehmann, who in 1936 discovered the Earth has a solid inner core. Lehmann's basic method for studying the core with earthquake waves has remained much unchanged today. (Source: Vox)

More recently, it’s been found that the difference between such waves over the past ten years has become less pronounced, suggesting the Earth’s core is slowing down. This isn’t something to panic over. In fact, it’s a part of a rhythm of the Earth’s core that spans 70 year cycles as the core exceeds and then falls behind the Earth’s surface rotation. This happens because of two competing forces affecting the core: the molten metal of the outer core and the gravity of the mantle.

For the study, researchers Yi Yang and Xiaodong Song of Peking University in Beijing made use of seismic records of the past sixty years to track the dissonance between the waves of multiplet earthquakes—earthquakes that release multiple identical pulses. As these waves originate at the same velocity, the difference between them can be attributed to how they passed through the Earth’s core. By compiling this data, one can build a rough model of the core’s speeds over the past sixty years.

While the Earth’s core slowing down is nothing to worry about, much remains unknown about the iron ball at the center of our planet. The core’s inaccessibility leaves scientists with much to speculate, with only the distortions of earthquake waves to study it. But studying the core allows us to understand the forces that make life on Earth possible in the first place, as well as shed light on the formation of our planet. For now though our knowledge remains limited on the innermost part of our planet.