Love Thy Planet: That is the key takeaway from the news that Earth’s inner core has stopped turning

Just when people in the world’s largest democracy were busy discussing some fundamental philosophical issues related to the meaning of life — whether or not to see a film / documentary — a very ‘trivial’ thing happened. News came that the Earth’s inner core may have stopped turning. One may wonder, what’s the big deal in it? Why we should be concerned about that news?

Well, our planet Earth is a complicated and dynamic system. Also, what we know about our planet is limited to its surface known as the ‘crust’.

We dig the crust for various purposes like digging a well, mining and drilling in search of crude oil to name a few. We even build underground tunnels, metro stations and bunkers.

But each and every activity named here is limited to the crust. The deepest human-made hole is the Kola Superdeep Borehole SG-3 in Russian Siberia. Its depth is 12.3 km. It may sound big but compared to 6,371 km — the radius of the Earth — the depth of Superdeep Borehole SG-3 is a mere 0.2 per cent.

The crust is the thinnest layer of the Earth and measures about 40 km on average in depth, ranging from 5 kilometres to 70 km . At the scale of the planet, that’s less than the skin of an apple.

Next comes the ‘mantle’. It extends down 2,890 km, making it the thickest layer of the Earth. No human has managed to go to this layer to get a first-hand account. Most of the things we know about the mantle are from seismological studies.

The mantle is divided into the upper mantle and the lower mantle. There is a general consensus among scientists that the mantle is not in a steady state, but rather in a state of constant motion. There is convective circulation which actually directs the circulation of the plate tectonics in the crust.

Then comes the ‘core’. It lies deep in the centre of the Earth. It is made of iron and nickel with extremely high temperatures, about the same temperature as the surface of the Sun.

We sometimes refer to the core as one thing, although the inner core and the outer core are fundamentally different: The solid inner core and the liquid outer core. 

The Earth’s inner core is solid due to the fact that the immense pressure at that depth increases iron and nickel’s melting point to above these temperatures, resulting in the solidified core. Due to the presence of the liquid outer core, the inner core rotates. It’s just like a ball spinning inside a bigger ball. But at what speed?

The answer came from a very unusual quarter — the detonation of nuclear bombs. In September 1971, two nuclear bombs were detonated by the Soviet army. The powerful blast sent waves rippling so deep inside the Earth that they rebounded off the inner core.

John Vidale, a seismologist at the University of Southern California, along with Doug Dodge of Lawrence Livermore National Laboratory, used the scattered waves from these nuclear explosions to peep into the planet’s core.

They managed to calculate the speed of the rotation of the inner core. Their initial results, published in a 2000 Nature study, claimed a rotation rate of 0.15 degrees a year.

But the debate is still on as more and more scientists have come up with new estimates. For example, researchers from the Peking University analysed the seismic waves from earthquakes passing through the inner core since the 1960s and found that for decades, the travel times of these waves would vary in specific ways.

However, that variation vanished after 2009. In other words, the core’s rotation has ‘paused.’ However, that doesn’t mean that it’s not spinning at all.

Well, in reality, it means that the core’s rotation is now at par with the rotation at the surface. At different times, the core can race around or lag behind the surface. But even then, the difference is tiny. 

One may wonder if it is worthwhile to discuss the rotation of the inner core which we haven’t seen yet.

The answer is YES.  

The liquid metal in the outer core of the planet generates electric currents. Just like the dynamo of a bicycle, the rotation of the Earth on its axis causes these electric currents to turn our planet into a gigantic magnet, a bar magnet to be precise. 

This forms a magnetic field extending around the planet. The magnetic field is one of the most important factors in sustaining life on Earth. It acts as a shield and saves us from high amounts of radiation from the Sun. We see this as the form of auroras.

Our sun is a ball of superhot gases made up of electrically charged particles called ‘ions’ which continuously stream from the sun’s surface. These are called solar winds.

As a solar wind approaches the Earth, it meets the Earth’s magnetic field and most of it is blocked by the magnetosphere. However, some of the ions are trapped in a region of the atmosphere called the ionosphere.

In the ionosphere, the ions of the solar wind collide with oxygen and nitrogen atoms from the Earth’s atmosphere. The energy released during these collisions causes a colorful glowing halo around our poles namely the Aurora Borealis, the Northern lights, and Aurora Australis or the Southern lights.

Besides shielding us from the solar wind, this magnetic property also saves our atmosphere from leaking into space. Our neighbouring planet Mars is a fit case to understand the importance of the presence of Iron-nickel in the core of our planet.

We have been trying hard to develop human habitation on Mars, but Mars has a problem. It doesn’t have liquid metal in its core and because of that, it doesn’t produce a dynamo effect like Earth. 

In other words, the Red Planet has a very weak magnetic field. Because of a weak magnetic field, its atmosphere is stripped away by solar winds, leaving it uninhabitable.

Interestingly, Venus or the ‘twin planet of Earth’ has a core of iron and nickel as well. But Venus’ atmosphere is one of the extremes. It has the hottest surface in the solar system, hotter even than Mercury, the innermost planet.

Why? Because of greenhouse effect. The atmosphere of Venus is mostly carbon dioxide with clouds composed of sulphuric acid. And at the surface, the hot, high-pressure carbon dioxide behaves in a corrosive fashion.

Even though Venus is similar in size to Earth and has a similar-sized iron core, the planet does not have its own internally generated magnetic field. Instead, Venus has what is known as an induced magnetic field.

When the Sun’s magnetic field interacts with the electrically excited ionosphere of Venus, it creates or induces, a magnetic field there. This induced magnetic field envelops the planet and is shaped like an extended teardrop, or the tail of a comet, as the solar wind blows past Venus and outward into the solar system.

To cut a long story short, Venus is also not inhabitable. We can’t relocate to Mars or Venus. Mercury is too close to the Sun and others are gas giants.

Now if the findings about the stopping of the rotation of the core are true, does this mean that our planet is also going to lose its atmosphere? Are we going to die?

The bad news is we are clueless and helpless. The chilling truth is if something of that sort happens we can’t do anything. We don’t have the technology to have any direct interaction with the core, let alone have any technology to control its spin. If something of that sort happens we don’t have any other option but to accept it.

The good news, according to the researchers, is the change in the speed and the direction of the rotation of the inner core of the earth is all part of a 70-year cycle.

Scientists have found evidence that the previous reversal took place in the early 1970s. The cause of this cycle could be several major competing forces. The magnetic field generated by the outer core could be speeding up the inner core’s spin, while the huge gravitational influence of the mantle could drag on it and slow its spin.

One may say that this is a way of our planet telling us a simple thing: Love thy life on me. I am your only home in this vast universe.

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