Earth’s Inner Core May Have Stopped Spinning
The Earth’s solid inner core is about 2,200 miles below the surface, which makes up one-third of its mass. Mainly made of iron and nickel. Seismic waves have helped scientists learn about the core.Which consists of a molten metal outer core and a liquid mantle. The two layers interact with each other, generating electromagnetic forces that influence the core to spin.
Seismic data
The Earth is made up of three layers: the crust, mantle, and inner core. Each of which revolves at a different speed than the rest of the planet. The earth’s inner core (located around 3,200 miles beneath the surface of the Earth) is separated from the semi-solid mantle by a liquid outer core. That allows it to rotate at a slower rate than the rest of the planet.
The outer and inner cores contain about one-third of the planet’s total mass. Scientists have been trying to figure out the inner core’s rotation since 1996. When there was reported evidence of slight temporal changes in seismic waves that pass through it.
These seismic wave patterns were first interpreted by scientists as evidence that the core was rotating in an extra-fast direction. Later studies refined estimates of that’super-rotation’, finding that the inner core rotates faster than the mantle by about one-tenth of a degree per year.
But a recent study published suggests that the inner core may have stopped spinning.
In this new study, the researchers pored over data from earthquakes that triggered pairs of seismic waves called “doublets”. Looking between 1960 and 2009 to see if they could identify changes in the time it takes these waves to travel through the core.
According to the study, the waves from these doublets traveled at varying rates through the core before 2009. But since 2009, they’ve shown little variation.
The difference isn’t big, but it suggests that the core is now in lockstep with the surface’s rotation.
This is a significant discovery, but not necessarily the end of debates about how fast the core rotates. Some geophysicists still think that the inner core isn’t rotating at all. But, rather that the boundary between it and the outer core grows or shrinks over time.
Regardless, more data is needed to determine the real meaning of these seismic wave patterns. Ultimately, they may prove to be helpful in explaining other geophysical phenomena that occur on Earth. Such as 60- to 70-year variations in the length of its days.
The magnetic field
Magnetic fields that helps to keep us afloat is produced by molten iron and nickel within the liquid outer core of Earth. As the molten metal moves, it creates electrical currents that produce these results.
Researchers are looking at the core’s rotation to see whether it’s spinning faster than it should be. They’ve been able to do this by analyzing seismic waves that are reverberating deep in the Earth’s core.
According to their research, the inner core may have stopped spinning. Or it could have started to spin in the opposite direction instead. This doesn’t mean the whole planet has stopped rotating. As the gravitational forces still pull on the rest of the planet and cause it to move around.
But it does suggest that the whole process may have been going on for a while. They’ve been able to show this by looking at seismic data from earthquakes that have passed through the inner core over the past 70 years. And they’ve found that it’s been pausing and then starting to spin in a new direction every about 30 years.
These changes in the core’s rotation could be caused by the huge magnetic force affecting it. Or by its enormous gravitational influence on the mantle. Maybe even caused by the core’s changing temperature. Which in turn affects the magnetic field.
The team studied rocks from 600 million to 1 billion years ago.That contained tiny needle-shaped crystals of the mineral titanomagnetite. Which record the strength of the magnetic field when they formed. They found that the magnetic field was one-tenth as strong then as it is now.
They then looked at how the magnetic field changes when heat is transferred from the core to the mantle. Finding that when there’s less heat flowing from the core. The Earth’s magnetic field is more like a dipole with opposing north and south poles. Then when there’s more heat transfer from the core to the mantle. The magnetic field is less like a dipole and reverses more frequently.
The mantle
The mantle is Earth’s most dense layer, made of iron- and magnesium-rich silicate rock. It forms about 83 percent of the planet’s volume and extends from Moho’s discontinuity to 2,900 km beneath the asthenosphere. It has a temperature range from about 200 degC at the upper boundary with the crust to approximately 4,000 degC at the core-mantle boundary.
Its high heat and pressure cause the rocks in the mantle to be ductile, but not brittle. This is a big reason why earthquakes occur in the mantle.
When a large earthquake occurs, it emits primary, or pressure, waves that travel in all directions. Secondary, or shear, waves follow.
Seismologists are able to see these P and S waves because they can bend and reflect off Earth’s interior layers. But if the iron core were liquid, then it would be too hard for those waves to travel through it.
But that didn’t change the fact that scientists had observed an odd pause in the inner core’s rotation relative to the mantle. Which they believed could be a sign of something brewing deep in Earth. The pauses appeared around 1971 and 2009, and some researchers speculated the change was related to Earth’s magnetic dynamo.
This dynamo is responsible for generating Earth’s magnetic field and balancing the forces between the outer and inner cores. Knowing how the inner core rotates could help scientists better understand these interactions. And may even shed light on other processes in Earth’s interior.
In the past, many geophysicists believed that the inner core spun at the same rate as the mantle. But as this idea grew more complex, it began to look less likely.
The core’s motion
Seismologists have long been fascinated by the Earth’s inner core. The solid metal marble within the liquid outer core – but understanding what it does is still a mystery. The deep interior of the planet is too remote to observe. Which means scientists must rely on information about it that can be gathered from seismic waves. And other measurements that travel through it.
As it turns out, the inner core has a way of changing its motion over time. This is why the core’s spin isn’t always a perfect mirror of the planet’s rotation. It can race around or lag behind. Depending on the amount of molten iron in the outer core that’s moving and how close it is to Earth’s surface.
That has left some researchers with questions about how the core’s rotation affects Earth. For example, scientists have wondered if the change in core rotation might be contributing to fluctuations in the planet’s magnetic field. But those theories may not be necessarily a danger to life on the surface. As the variation in rotation time isn’t dramatic and doesn’t pose a threat to the stability of Earth’s magnetic field.
Rather, the changes in the core’s rotation seem to be an effect of the core’s shifting topography. That’s because the inner core isn’t a ball of smooth, stationary iron but an uneven, fluctuating mass.
But while the changes in the core’s rotation are an accurate reflection of its changing topography. It’s believed to be wrong to interpret those same changes as evidence that the core’s rotation may be slowing.
Provided by Antonio Westley
Disclaimer: This article is meant to be seen as an overview of this subject and not a reflection of viewpoints or opinions as nothing is definitive. So, make sure to do your research and feel free to use this information at your own discretion.
