What slows the core

The Earth’s inner core is a hot and massive sphere of 100 quintillion tonnes of iron and nickel, resting ~5,150 km beneath our feet. It’s a rotating world, which is now slowing down, potentially altering time on the surface
Earth’s inner core
Earth’s inner core

Deep below the Earth’s surface on which we stand, move about, and life continues, is an intensely hot hub of seismic and geological activity.

Planet Earth is a complex ball of rock, metals, and minerals, held together by gravity. The structure of the planet is divided into four major layers: the crust (which is right beneath our feet) – made up mostly of rock, 4.8-69-km thick); the mantle – composed of silicates, 2,900-km thick; the outer core – composed of liquid iron and nickel, 2,200-km thick; and the inner core – the radius of the planet, which is made up of blazing hot iron, nickel and sulphur, 1,200-km thick. Each layer has a unique chemical composition, mechanics, and physical state, which can impact life on Earth’s surface.

It is theoretically impossible to venture to the deepest central point below the Earth’s surface. Information about the core mostly comes from the analyses of seismic waves and the planet’s magnetic field. However, research is certain that the temperature rises exponentially, deeper into the Earth’s surface. The Earth’s centre – the inner core – is its hottest layer, with temperatures up to 5,500 degrees Celsius. Due to its immense heat energy discharge, the inner core is considered to be the Earth’s engine room. The inner core’s actions determine how Earth’s other properties, including life, play out.

Primarily, the Earth’s core is responsible for the generation of the planet’s magnetic field, and contains information regarding the earliest history of its accretion. When the core formed, some thermal and compositional features were established which controlled its subsequent evolution. These features also influenced the evolution of the mantle, crust, and the atmosphere.

According to the Australian National University, despite its small volume (less than 1% of the Earth’s volume), the inner core contains about 10% of the total magnetic field energy. “The inner core plays a crucial role in outer core liquid motions and the geodynamo, which generates the Earth’s magnetic field. Without the magnetic field, life on Earth would be impossible,” it says.

The magnetic field thus generated protects the planet from cosmic radiation of the Sun’s charged particles. It also provides direction for navigation on the planet’s surface by demarcating poles, distinguishes regions on the Earth, and balances the natural order of things. Scientists also suggest that movement in the mantle caused by variations in heat from the core, causes the seismic plates to shift, which can trigger earthquakes and volcanic eruptions. These natural calamitous occurrences change our landscape, and threaten lives and property.

Rotation puzzle

The Earth’s rotation singularly depends on the functioning of the inner core, which also determines the prevalence of day and night.

At the equator, the distance covered is equal to Earth’s circumference of 40,075 km, and the average speed of the planet’s rotation is about 1,670 kmph. Scientific models have predicted that the inner core rotates 3 degrees per year faster than the mantle, a phenomenon that is known as ‘super-rotation’. Movement of the inner core has been debated by the scientific community for two decades, with some research indicating that it rotates faster than the planet’s surface.

In 2004, the National Science Foundation’s Earth Sciences Division had analysed that the inner core rotates in the same direction as the Earth, but slightly faster. However, a new study has provided “unambiguous evidence” that the Earth’s inner core began to slow down its rotation since 2010, compared to the planet’s surface. Researchers have said that the slowing down could change the length of a day on the Earth by fractions of a second. Scientists at the University of Southern California (USC) have proven that the Earth’s inner core is backtracking – slowing down – in relation to the planet’s surface, as shown in new research published in the journal, Nature.

“When I first saw the seismograms that hinted at this change, I was stumped,” says John Vidale, Dean’s Professor of Earth Sciences at the USC Dornsife College of Letters, Arts and Sciences, adding, “But when we found two dozen more observations signalling the same pattern, the result was inescapable. The inner core had slowed down for the first time in many decades. Other scientists have recently argued for similar and different models, but our latest study provides the most convincing resolution.” The inner core is considered to be reversing and backtracking relative to the planet’s surface due to moving slightly slower instead of faster than the Earth’s mantle for the first time in approximately 40 years. Relative to its speed in previous decades, the inner core is slowing down. Vidale and Wei Wang of the Chinese Academy of Sciences utilised waveforms and repeating earthquakes in contrast to other studies. Repeating earthquakes are seismic events that occur at the same location to produce identical seismograms.

In this study, the researchers compiled and analysed seismic data recorded around the South Sandwich Islands in the South Atlantic from 121 repeating earthquakes that occurred between 1991 and 2023. They also utilised data from twin Soviet nuclear tests between 1971 and 1974, as well as repeated French and American nuclear tests from other studies of the inner core. According to Vidale’s analysis, the inner core’s slowing speed was caused by the churning of the liquid iron outer core that surrounds it, which generates the Earth’s magnetic field, as well as gravitational tugs from the dense regions of the overlying rocky mantle. Impact on the surface The inner core can neither be visited or viewed.

Hence, the implications of this change in the inner core’s movement for Earth’s surface can only be speculated. Vidale says the backtracking of the inner core may alter the length of a day by fractions of a second: “It’s very hard to notice, on the order of a thousandth of a second, almost lost in the noise of the churning ocean sand atmosphere.” The USC scientists now aspire to chart the trajectory of the inner core in even greater detail to reveal exactly why it is shifting. “The dance of the inner core might be even more lively than we know so far,” Vidale concludes. What lies beneath, only time will tell!

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The New Indian Express