Earth’s Core Just Started Spinning Backwards | DNA

Over 3,000 miles below the surface, right at the center of the Earth, lies a solid spheroid primarily made of iron. This hidden world is nearly as big as the moon, and its temperature rivals that of the sun. This is Earth’s inner core, an independent engine spinning at the very heart of our planet.

While we cannot see it for ourselves, its immense heat triggers processes that impact us all. It drives the plate tectonics that manifest in some of the most awe-inspiring and deadly sights on the surface. It also generates our planet’s invisible magnetic field, which shields us and makes life possible.

It is no wonder that Earth’s core has captured the imaginations of generations of scientists. These researchers have developed ever more sophisticated instruments to investigate its fiery, unreachable depths. The latest research efforts have yielded discoveries that could have come straight from a Hollywood film.

Our inner core appears to not only have stopped spinning, but has in fact started moving backwards. Why has this happened, and what does it mean for us topside? To understand this twist, we must explore our planet’s deepest, darkest secrets.

We will investigate its inner workings, assess the implications of our core’s change in motion, and ask the critical question: how worried should we be? In order to get to our planet’s core, we need to go down. Call it a modern journey to the center of the Earth.

Each layer has its own role in creating, sustaining, and sometimes destroying the world above. All of them are influenced by the solid iron heart at the center. Here at the surface, we walk upon the crust, which is a mere brittle shell.

Though it feels pretty solid to us, it is in fact fractured into giant tectonic plates. These plates drift, collide, and grind past each other, causing violent earthquakes and devastating volcanic eruptions. How it moves is all thanks to the layer directly below, known as the mantle.

The mantle layer also appears solid, but is actually flowing very, very slowly. It moves at the rate of a few centimeters a year. This tiny but inexorable movement contributes directly to the plate tectonics that impact our surface world.

Dig deeper still and you reach the outer core, a churning sea of liquid iron and nickel. This liquid layer generates its own heat-driven currents. Its constant motion generates the Earth’s magnetic field, which protects life on our planet from deadly solar particles.

Finally, suspended within this liquid outer core is that primarily iron inner core. Here, the temperature reaches a staggering 6,000°C. Due to the immense pressures, the metal isn’t liquid, but solid, forming a slightly squashed sphere.

This is our planet’s boiler room, a powerhouse of heat. Its energy triggers the processes in the layers above, driving those all-important convection currents in the outer core. Ultimately, this heat contributes to the plate tectonics that shift the Earth’s crust.

It is easy to take for granted that we understand our planet’s structure. In reality, that knowledge was incredibly hard-won by early pioneers. It is one thing studying, cataloging, and theorizing about the world we can see all around us.

It is quite another to investigate our planet’s hidden interior. So, how do we actually know what is down there? In Frankfurt, September 1896, darkness was falling as a 34-year-old Emil Wiechert waited for his chance to speak.

He was attending a meeting of German scientists and physicists, clutched in his hands his latest research. His work proposed a solution to a problem that had plagued the scientific community for more than a century. The average density of planet Earth had been calculated at around 5.5 grams per cubic centimeter.

Yet, surface rocks have a density of around half that amount. So, where was all that missing mass hiding? One theory was that the Earth gets progressively denser nearer the center.

But that was not good enough for Wiechert, who reasoned that molecules in a solid are already pretty densely packed. Even the compressional effects of high pressure would not be enough to achieve the density required. When he finally got the chance to speak, he proposed something else.

His theory was that the density difference must be due to a different, much denser material. He believed this material was hidden deep in Earth’s interior. As to what that material could be, the inspiration for his theories came from the heavens.

He looked at iron meteorites, which are little clumps of metal with a density higher than Earth’s average. Wiechert reasoned that our planet’s interior must therefore contain a large iron core. This core would be dense enough to account for the difference between lighter surface rocks and the higher planetary average.

Now, this was not an entirely new idea in the scientific community. However, Wiechert deployed mathematical reasoning rather than the purely theoretical work of his forebears. He also proposed it at just the right time, as a new technology was emerging.

This technology would finally allow the interior of the Earth to be studied scientifically. Earth’s core is so deep, and the pressures and temperatures so intense, that you cannot simply drill down. You cannot just take a sample, although that would be nice.

Even today, our deepest man-made hole is the Kola Superdeep Borehole in Russia. At more than 12 kilometers deep, that is still only a fraction of a percent of the way there. To be exact, it is just 0.2 percent of the distance to the center.

In order to study the core, scientists rely on measurements taken here on the surface. Thankfully, there is one way we can get particularly insightful information, and that is from earthquakes. By the 19th century, increased interest in seismic activity prompted the creation of a measuring device.

This device was the modern seismograph, and it changed how we view the planet. For the first time, the analysis of seismic events was not based on eyewitness observation. It relied on quantifiable data instead of mere hearsay, which is a massive leap forward.

While the device itself was unquestionably a scientific breakthrough, the real magic happened next. The invention spread across the globe, creating an interconnected network. As seismographic networks expanded, scientists found they could detect earthquakes happening far away.

They could even record events occurring on the other side of the planet. In 1897, the great earthquake erupted at the Shillong Plateau in India. Shocks were felt in Kolkata and even as far away as Burma.

Seismographs detected this earthquake much further away in Europe. The resulting seismograms were poured over by British geologist Richard Dixon Oldham. Oldham was the leader of the Geological Survey of India at the time.

He noticed that the seismograms showed three distinct wave shapes. In his papers, he compared the data found from this and several other earthquakes. He found that they too showed the same three waves.

The reason he could see them so clearly was being far from the epicenter. Differing speeds of the waves meant they arrived one at a time. The first arrivals were later known as primary waves, or P-waves.

These are longitudinal pressure waves that oscillate in the same direction as they are traveling. These were then followed by secondary shear waves, or S-waves. S-waves are transverse, meaning their oscillations are perpendicular to their direction of travel.

Finally, surface waves ripple through the Earth’s crust itself. It is these surface waves that tend to cause the most destruction. It had already been established by this point that longitudinal waves can pass through both solids and liquids.

However, transverse waves can only pass through solids. You can probably see where this realization is going. Since the seismic waves had traveled through the inside of Earth, they held secrets.

The resulting seismographs could yield information about what they passed through. This meant they could map the very structure of Earth itself. This realization would allow centuries of speculation to finally be put to rest.

Put simply, Oldham noticed something strange about the waves that traveled a long way. They seemed to travel much slower than the 6 kilometers per second usually observed. Usually, they moved through the mantle at that higher speed.

To explain this, he concluded that they had traversed a central core. This core was composed of matter which transmits them at a slower speed. He noted that this speed was exactly 3 kilometers per second.

He calculated the size of this core to be four-tenths of the Earth’s radius. He deduced that it bends earthquake waves as they pass through. He also proved that it behaves fundamentally differently to the rest of the Earth’s interior.

However, he did not speculate as to what this core might be made of. He refused to go beyond what he could prove with hard data. By the early 20th century, you had a theory that the Earth had an iron core.

You also had apparent proof that some sort of core did in fact exist. We were finally beginning to crack the inner structure of our planet. Yet, despite these great strides, these early pioneers missed something crucial.

Sometimes, scientists get so focused on all the awesome stuff happening below our feet. They forget that the stuff on land also needs a bit of love, too. Perhaps now more than ever, environmental preservation requires our attention.

Organizations around the world are fighting back against habitat destruction. Many community-based nature protection groups are stepping up to restore ecosystems. They fund projects to restore nature around the world and document the impact.

This visual transparency inspires people to get involved in sustainability. With so much plastic waste around, breakthroughs are needed to stop plastic from reaching oceans. People with backgrounds in sustainability are very personally invested in these causes.

Getting involved gives individuals a chance to see results in less than 30 days. This connection between human action and planetary health mirrors our journey into the Earth. As we head back to the science, the data continues to pile up.

As seismographs continued to spread around the world, more and more data was gathered. Scientists noticed that S-waves did not register on some seismographs at all. Something deep inside the planet was stopping them in their tracks.

Remember that S-waves do not transmit through liquids. It was a small leap, therefore, to go from that fact to a bold new idea. Scientists realized that Earth’s core must therefore be liquid iron.

This idea was not completely wrong, but there was something they had all missed. It took a brilliant Danish scientist to find the missing piece. In 1929, Inge Lehmann was chief of the seismological department in Denmark.

She worked at the Denmark State Geodetic University, managing the stations. Her responsibilities involved keeping the instruments correctly adjusted and interpreting the seismograms. She was also responsible for publishing the bulletins of the seismic stations.

However, her official job did not extend to original research. When she decided to embark on her own research project, she had to do so alone. She worked without the typical team of assistants to help her analyze the data.

It was precisely because she was forced to troll through so much data by herself. She noticed something odd about the P-waves she was studying so intently. You see, if the Earth had a completely liquid core, P-waves should behave predictably.

They should travel down from an earthquake, reach that core, and be refracted. This refraction happens due to the liquid’s properties, like light entering a prism. The expected result would be a massive shadow zone on the surface.

No P-waves would appear in this zone because they had all been refracted away. Yet, after a massive earthquake in New Zealand, she discovered something impossible. She found P-waves in the shadow zone, precisely where they should not be.

In a research paper titled simply “P,” she attempted to explain what she had seen. She reconciled it with existing observations and concluded that the core had two parts. There was an outer core that was liquid and so stopped the S-waves.

Crucially, there was also an inner core that was solid. This solid core could transmit some P-waves to the shadow zone where she had seen them. As a woman working in the male-dominated world of science, Inge had to fight.

She fought to have her conclusions heard, but she would turn out to be absolutely correct. That solid inner core was the final piece of the structural puzzle. However, as is often the way with scientific research, this discovery brought new questions.

Since the solid inner core is held within a liquid outer core, it is suspended. Does it necessarily spin in sync with the rest of the planet? Or could it be rotating at its own independent speed?

To find out, scientists would require incredibly sophisticated seismographs. They would soon have access to such instruments, though the source was unexpected. It would not be thanks to pure science alone, but to war.

By the second half of the 20th century, the world was in the Cold War. While the general public lived with the constant specter of nuclear Armageddon. For seismologists, it was proving to be a time of incredible scientific excitement.

The United States instigated a massive program called Project Vela Uniform. Its aim was to develop a suitable system for detecting underground nuclear testing. They wanted to monitor activities inside the Soviet Union accurately.

What resulted was an investment of over half a billion dollars in today’s money. This funding poured directly into seismographic technology and worldwide networks. Crucial to the project’s success was a specific capability.

Scientists needed to distinguish between the seismic waves produced by nuclear tests. They had to separate them from those made by naturally occurring earthquakes. By the time the Cold War ended, researchers at Harvard University made breakthroughs.

Using these advanced seismographs, they showed something fascinating about seismic waves. Waves traveling along Earth’s north-south axis through the inner core moved faster. They outpaced those undertaking the journey in an east-west direction.

To explain this speed difference, they theorized that the core is anisotropic. This means it has a crystalline structure aligned with Earth’s rotation. This alignment is roughly along its magnetic field lines.

Think of it like the grain on a plank of wood. Just as a plank of wood is easier to mill in one direction. It is easier for earthquake waves to pass through the core this way.

They move faster on the north-south axis than the east-west axis. Well, it turns out that this crystalline structure is not perfectly aligned. It does not align precisely with the rotation of the Earth.

Instead, the structure is tilted a few degrees off-axis. This was crucial because it gave scientists a potential way of measuring spin. They could determine how fast the inner core spins relative to the crust.

If it spins at a different rate to the rest of the planet, things change. That movement would continually change the way those crystals are aligned. This change would in turn affect the wave travel times over the years.

This realization gave birth to a method of assessing inner core spin. This very method is still used by researchers to this day. Working out whether Earth’s core was spinning at its own rate was difficult.

Scientists recognized they needed data from multiple specific earthquakes. These earthquakes had to have happened in nearly the exact same spot. They also needed to be far enough apart in time for the core to move.

Fortunately, they had decades of earthquake data thanks to the Cold War. The hunt was on for what they termed earthquake doublets. Now, such doublets are incredibly rare in nature.

Imagine hunting for identical twins when they are sat in different parts of a crowd. Picture them in a massive crowd at Wembley Stadium, and you get the idea. Fortunately, it was no longer the era of pen and paper analysis.

With the increased digitization of seismic data, everything changed for the better. What would have once been thousands of human hours was now automated. The work was handed over to advanced computer algorithms.

By 1996, a team of researchers at Columbia University found their target. They discovered data from a series of earthquakes in close proximity. These events took place at the South Sandwich Islands.

Crucially, a seismic station had reliably monitored them for 32 years. This station was located in College, Alaska, providing a consistent record. By comparing the readings, they found something remarkable.

From 1967 to 1995, these similar waves were changing. They were taking a faster and faster path through the Earth’s core. They finally had their answer after years of searching.

Earth’s core must have rotated at a different speed to the rest of the planet. It was the first observational evidence of inner core rotation ever recorded. They calculated that it was spinning faster than its surroundings.

With the technique proven, the scientific floodgates opened wide. In the last couple of decades, many studies have been published. Some agree the core rotates faster, while others conclude it spins more slowly.

Further studies have suggested that the rotation actually fluctuates over time. Sometimes it spins faster, and other times it moves slower. This change might happen as frequently as every couple of years.

So, what is actually going on down there, and who is right? In 2023, scientists at Peking University in Beijing published a paper. They argued that inner core rotation has nearly paused recently.

Relative to the mantle, it has been rotating slightly backwards over the past decade. They stated that such a change of rotation also occurred before. Specifically, a similar shift happened in the early 1970s.

They ultimately concluded that the Earth’s inner core oscillates. It goes back and forth with a period of about 70 years. The following year, another study was produced to test this idea.

This time, the study came from the University of Southern California. They approached the same problem from a subtly different angle. Rather than looking for differences in waves from the same earthquakes.

It looked for matching waveforms from entirely different times. They reasoned that if previous studies were correct about the cycle. If the inner core went through a cycle of faster and slower rotation.

Then there would be times where it returned to the same position. It would be back in the same position relative to the mantle. I think of this like a car and a bus driving together.

Imagine them traveling in the same direction side by side on a highway. If the car alternates between traveling slower and faster than the bus. There will be times when it is ahead of the bus.

There will be times when it falls behind the bus. And there will be times when it is back aligned with the bus again. The study examined P-waves produced from 121 earthquakes.

These events took place between 1991 and 2023 in the South Sandwich Islands. The waves passed through the Earth’s inner core during their journey. They were detected by seismometers in Alaska and Canada.

Using this methodology, they confirmed the findings of the previous year. The changes in the inner core’s rotation speed follow a 70-year cycle. According to their calculations, it is just about due to speed up again.

As for what causes this massive change, scientists are not yet certain. Possibly, the magnetic field of the liquid outer core drives it. It could drag on the solid iron within, speeding it up or slowing it down.

At the same time, gravity from dense regions in the mantle could pull. It could tug on variations in the inner core, affecting its rotation. But what does that mean for us living on the surface?

Do we need to worry about this deep planetary shift? Remember how I said earlier that the inner core is the boiler room. It is the powerhouse of our planet, influencing the layers above.

It turns out that changes in its behavior do correlate with surface phenomena. The authors of the 2023 study noticed something interesting. That 70-year oscillation coincides with fluctuations in the length of a day.

It also correlates with minor changes in the magnetic field. Beyond that, they even link them to changes in global mean temperature. They noted a connection to sea level fluctuations as well.

Before you get too alarmed by these findings, look closer. We are talking about tiny changes here on the surface. We are looking at a thousandth of a second difference in a day.

We are seeing a fraction of a degree change in temperature. This is certainly not enough to explain modern global warming trends. The long story short is that it is still early days for this science.

Scientists are continuing to study the inner core and its impacts. They want to fully understand the world above us. Every passing year yields more and more seismic data ripe for analysis.

New insights are only a matter of time with better technology. Perhaps Inge Lehmann put it best a few years before her death. She passed away at the ripe old age of 104, leaving a legacy.

She wrote that the first results for the properties were naturally approximate. Much has been written about it since then, she noted. But the last word has probably not yet been said.

Think about this deep, independent engine spinning beneath us. Is this planetary cycle something we should worry about? How do you think this will affect life on Earth, if at all?

It appears that when it comes to the deepest secrets, we are learning. Our planet holds mysteries that we are still trying to unravel. We really are still only scraping the surface of this inner world.