earth's inner core
Julie Hambleton
Julie Hambleton
March 5, 2024 ·  3 min read

Earth’s Spinning Inner Core Recently Paused Then Flipped Its Direction

The inner core of our planet is a solid ball of iron and nickel that’s about as big as Mars. It’s always been there, but recently it paused and then flipped its direction. The change was so small that we couldn’t see it from the surface. However, it’s enough to affect our planet’s magnetic field in a way that could have serious consequences for life on Earth.

The Earth’s Inner Core Is Now Spinning In The Opposite Direction As Before

The Earth’s inner core rotates opposite from the rest of Earth’s mantle and crust. This is because it formed at much lower temperatures than the other layers. However, scientists have found that this rotation has changed–and they don’t know why. (1)

The inner core is about 2,400 kilometers (1,500 miles) thick and has a diameter of about 870 kilometers (540 miles). It’s made mostly of iron and nickel. Scientists think that its solid ball of iron and nickel is oriented in the same direction as Earth’s magnetic field, but recent research shows that this isn’t the case any longer.

How The Scientists Detected It

In a study published in Nature Geoscience on Monday, researchers explain how they could detect this change using seismic waves generated by earthquakes. They found that while seismic waves travel faster through the outer core than through the mantle or crust, they travel slower through both parts of the inner core than they used to–and this change happened suddenly around 2002-2003. The researchers suggest that this is because of a change in the orientation of Earth’s inner core. It’s possible that the solid ball of iron and nickel has flipped over, which would explain why seismic waves now take longer to travel through both parts of the inner core.

“The evidence for the reversing since 2009 is quite strong—statistically over 95 percent confidence level,” the research team said. “These results help us better understand how the inside of the Earth operates and how the different layers of the system interact as a whole. Such multi-decadal oscillations also exist in the other Earth layers, such as the outer core, mantle and surface, indicating a possible resonating Earth system.” (2)

Why Did It Flip?

But why would this happen? The researchers say there are two possible explanations: either an increase in temperature or decrease in pressure within the inner core itself or an increase in temperature or decrease in pressure outside of it (meaning closer to us). The researchers say that the latter explanation is more likely. According to them, there’s evidence that Earth’s magnetic field could have reversed at some point in the recent past. This would have caused a change in pressure or temperature outside of the inner core and made it easier for seismic waves to travel through both parts of it.

The researchers say that the evidence for this is in the fact that certain minerals found within the inner core have been dated to around 1.5 billion years old, while others are only a few hundred million years old. This could mean that there was a reversal at some point in Earth’s history and that it happened more recently than we thought.

The inner core is believed to have formed almost one billion years ago, but there’s some evidence that it could have formed more recently. A study published in the journal Geophysical Research Letters suggests that Earth has experienced at least two magnetic field reversals in the past 3 million years. This would be consistent with earlier studies that found evidence of magnetic fields reversing themselves over short periods of time during Earth’s history. (3)

How Will This Affect Us?

So what does this flip mean for us? When this happens, it could mean there are changes in weather patterns or other natural phenomena we experience on Earth. When there are changes in Earth’s magnetic field, it can disrupt satellites and communications systems as well as affect animal behavior and migration patterns. The flip doesn’t necessarily mean Earth will experience any major changes, though. We don’t know if the reversal will be a quick one or if it will take hundreds of thousands of years.

Keep Reading: Scientists Detect Signs of a Hidden Structure Inside Earth’s Core


  1. Multidecadal variation of the Earth’s inner-core rotation.” Nature. Yi Yang and Xiaodong Song. December 21, 2021.
  2. Earth’s Inner Core May Have Started Rotating in the Opposite Direction.” Newsweek. Aristos Georgio. January 23, 2023
  3. Earth’s magnetic field is probably not reversing.” PNAS. Maxwell Brown, et al. April 30, 2018.