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What lies at the centre of the Earth?

How is the Earth structured?

While technological advances have taken mankind to the Moon, we have not even come close to reaching the centre of our own planet, having ventured no further down than the 7.6-mile Kola Superdeep Borehole drilled in Soviet Russia in 1965.

That’s nothing when you consider that the absolute centre of Earth’s core lies 3,728 miles beneath the surface.

Our planet is essentially composed of three layers: the core (consisting of inner and outer zones), the mantle and the crust.

The spherical inner core of our globe, roughly the size of the Moon, is primarily made up of iron, seething at the extremely high temperature of approximately 5,200C, which is well above the metal’s boiling point. It retains its solid shape because of the extreme pressure it is subjected to from the outer layers, which serves to contain it.

The outer core, composed of churning molten iron and nickel, is also extremely hot, existing at temperatures anywhere between 4,500C and 5,500C. The edge of the outer core lies about 1,800 miles below the surface of the Earth.

Wrapped around that lies the mantle, which is an estimated 1,800 miles thick and accounts for around 84 per cent of the volume of the entire planet. It is cooler than the core at 3,700C and contains oxygen and silicon within its mostly solid constitution plus traces of iron, aluminium, calcium, sodium and potassium.

The outermost layer or crust - where all life resides - is just 25 miles deep and accounts for just one per cent of the Earth’s mass, consisting of the rocks and minerals that make up the tectonic plates of our surface. It is their constant slow shifting that causes mountains and ridges to form, volcanoes to erupt and earthquakes to rattle our world.

What was historically believed to lie at the centre of our planet?

The mystery of what might lie at the heart of our globe has fascinated man for centuries - dating back as far as the Ancient Greek conception of an underworld lying beneath our feet and the sulphurous Hell of Judeo-Christian imagination - but the most famous and fantastical exploration of the theme comes from French science fiction writer Jules Verne and his novel Journey to the Centre of the Earth (1864).

Verne’s story imagines German scientist Professor Otto Lidenbrock descending into the bowels of the Earth in the company of his nephew Axel and their Icelandic guide Hans via the Snaefellsjokull volcano and encountering a subterranean world of catacombs, petrified plant life, sentient mushrooms and deep oceans populated by prehistoric sea monsters.

Other writers to address the “hollow earth” theme in their work include Ludvig Holberg, Giacomo Casanova, Edgar Allan Poe, Georges Sand, WH Hudson, John Uri Lloyd, Willis George Emerson, Edgar Rice Burroughs and Vladimir Obruchev.

That specific notion can be traced back much earlier to 17th century astronomer Edmund Halley, whose ideas were revived and developed later by John Cleves Symmes Jr in 1818.

More recently, their beliefs - which have been comprehensively debunked by subsequent science - have provided the basis for a bizarre conspiracy theory that posits that a superior race of extraterrestrials and “immortal escaped Nazis from World War II and the lost Viking colonies” live at the planet’s core, according to The Daily Mail.

“Instead of thinking that the world is flat,” the newspaper explains, these self-identifying “Hollow Earthers” are convinced “that it actually contains a paradise at its core that resembles the Garden of Eden”, with adherents even attempting to mount an expedition to the North Pole in 2007 to find an entrance portal under the leadership of author Rodney Cluff before the trip was aborted.

Why are we asking this now?

Scientists from Cambridge University and Nanyang Technological University in Singapore discovered last month that the collision of the tectonic plates making up the surface of the Earth plays a role in sequestering carbon within the planet’s core.

Their research, published in the academic journal Nature Communications, concluded that the carbon drawn into Earth’s super-heated interior tends to stay locked away at depth, rather than then resurfacing in the form of volcanic emissions.

This could have implications for understanding the climate emergency and the greenhouse effect in our atmosphere.

By studying how carbon behaves in the “deep Earth”, scientists can better understand its entire lifecycle on our planet and how it flows between the atmosphere, oceans and life at the surface.

Currently, the most closely studied parts of our planet’s carbon cycle are the processes occurring at or near the Earth’s surface. But deep carbon stores also play a key role in maintaining the habitability of our planet by regulating atmospheric carbon dioxide (CO2) levels, the scientists said.

There are a number of ways for carbon to be released into the Earth’s atmosphere as CO2, but there is only one path in which it can return to the Earth’s interior: via the slow business of plate subduction.

When this occurs, surface carbon, for instance in the form of seashells and micro-organisms that have locked atmospheric CO2 into their shells, is gobbled up into the Earth’s mantle.

Scientists had thought that much of this carbon was then returned to the atmosphere as CO2 via emissions from volcanoes. But the recent study suggest that chemical reactions taking place in rocks swallowed up at subduction zones trap carbon and send it deeper into Earth’s interior, thereby stopping some of it from being regurgitated to the surface. 

Reference: Independence: Joe Sommerlad