Category Science

         In 1990, a geological exploration began to find out more about the Earth’s crust. A hole drilled into the ground in the Kola Peninsula, Russia, has reached a depth of around 15km (9.3 miles). Nobody has been down it, and it is still well short of the Earth’s centre.

         Travelling to the Earth’s center is a popular theme in science fiction. Some subterranean fiction involves traveling to the Earth’s center and finding either a Hollow Earth or Earth’s molten core. Planetary scientist David J. Stevenson suggested sending a probe to the core as a thought experiment. Humans have drilled over 12 kilometers (7.67 miles) in the Sakhalin-I. In terms of depth below the surface, the Kola Superdeep Borehole SG-3 retains the world record at 12,262 metres (40,230 ft) in 1989 and still is the deepest artificial point on Earth.

         The idea of a so-called “Hollow Earth”, once popular in fantasy adventure literature, is that the planet Earth has a hollow interior and an inner surface habitable by human beings. Although the scientific community has made clear that this is pseudoscience, the idea nevertheless is a less popular feature of many fantasy and science fiction stories and of some conspiracy theories.

         The most famous example of a hollow-Earth fantasy is Jules Verne’s 1864 science-fiction novel Journey to the Center of the Earth, which has been adapted many times as a feature film and for television.

         The 2003 film The Core, loosely based on the novel Core, tells the story of a team that has to drill to the center of the Earth and detonate a series of nuclear explosions in order to restart the rotation of Earth’s core. The drilling equipment, dubbed Virgil, includes a powerful, snake-like laser drill, a small nuclear reactor for power, a shell (of “unobtainium”, a fictional material) to protect against intense heat and pressure (and generate energy to drive the engine), a powerful x-ray camera for viewing outside, and a system of impellers for movement and control. The only part of the Earth that turns out to be hollow is a gigantic geode, and soon after the drill moves through it, the hole it created fills with magma.

          The 1986 animated television show Inhumanoids featured regular visits to the Inner Core in most of its 13 episodes. Each of the three villainous creatures theoretically ruled over certain layers of the inner Earth, and their evil schemes were thwarted by the human Earth Corps, who often allied with various races of subterranean beings equally threatened by the Inhumanoids.

          During season 3 of the Teenage Mutant Ninja Turtles cartoon the Technodrome is located at the Earth’s core, and transport modules are used to drill up to the streets. This season also features the episode “Turtles at the Earth’s Core”, where a dinosaur lives in a deep cave, and a crystal of energy that works like the Sun to keep the dinosaurs alive. As Krang, Shredder, Bebop and Rocksteady steal the crystal to power the Technodrome, the trouble begins.

          Don Rosa’s 1995 Uncle Scrooge story The Universal Solvent imagines a way to travel to the planet’s core using 1950s technology, although this would be impossible in reality. The fictional solvent referred to in the story’s title has the power to condense everything except diamonds into a kind of super-dense dust. The solvent is accidentally spilled and, as it dissolves everything in its path, it bores a cylindrical shaft into the center of the planet. As part of a recovery effort, a makeshift platform is constructed that descends into the shaft in free fall, automatically deploying an electric motor and wheels as it approaches zero gravity, then using rocket engines to enable it to ascend again to the Earth’s surface. The author Rosa describes this fantasy journey in great detail: the supposed structure of the Earth is illustrated, and the shaft is kept in a vacuum to protect against the lethal several thousand kilometers of atmosphere that it would otherwise be exposed to. The ducks must wear space suits and go without food for several days, and they are not entirely certain that the super-dense heat shield will hold. The author maintains continuity with Carl Barks, explaining that the earthquakes in the story are created by spherical Fermies and Terries.

          In Tales to Astonish #2 (1959) “I Fell to the Center of the Earth”, an archaeologist named Dr. Burke who is on an expedition to Asia travels to the center of the Earth (and also, as he later finds out, backwards in time)–and encounters neanderthals and dinosaurs.

         In the Doctor Who episode, “The Runaway Bride”, a Racnoss warship is found at the center of the planet.

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          The outer core begins at a depth of 2935km (1822 miles) below the Earth’s surface. It is a further 3432km (2134 miles) to the very centre of the Earth.

          Earth’s core is the very hot, very dense center of our planet. The ball-shaped core lies beneath the cool, brittle crust and the mostly-solid mantle. The core is found about 2,900 kilometers (1,802 miles) below Earth’s surface, and has a radius of about 3,485 kilometers (2,165 miles).

          Planet Earth is older than the core. When Earth was formed about 4.5 billion years ago, it was a uniform ball of hot rock. Radioactive decay and leftover heat from planetary formation (the collision, accretion, and compression of space rocks) caused the ball to get even hotter. Eventually, after about 500 million years, our young planet’s temperature heated to the melting point of iron—about 1,538° Celsius (2,800° Fahrenheit). This pivotal moment in Earth’s history is called the iron catastrophe.

          The iron catastrophe allowed greater, more rapid movement of Earth’s molten, rocky material. Relatively buoyant material, such as silicates, water, and even air, stayed close to the planet’s exterior. These materials became the early mantle and crust. Droplets of iron, nickel, and other heavy metals gravitated to the center of Earth, becoming the early core. This important process is called planetary differentiation.

          Earth’s core is the furnace of the geothermal gradient. The geothermal gradient measures the increase of heat and pressure in Earth’s interior. The geothermal gradient is about 25° Celsius per kilometer of depth (1° Fahrenheit per 70 feet). The primary contributors to heat in the core are the decay of radioactive elements, leftover heat from planetary formation, and heat released as the liquid outer core solidifies near its boundary with the inner core. 

          Unlike the mineral-rich crust and mantle, the core is made almost entirely of metal—specifically, iron and nickel. The shorthand used for the core’s iron-nickel alloys is simply the elements’ chemical symbols.

          Elements that dissolve in iron, called siderophiles, are also found in the core. Because these elements are found much more rarely on Earth’s crust, many siderophiles are classified as “precious metals.” Siderophile elements include gold, platinum, and cobalt. 

          Another key element in Earth’s core is sulfur—in fact 90% of the sulfur on Earth is found in the core. The confirmed discovery of such vast amounts of sulfur helped explain a geologic mystery: If the core was primarily, why wasn’t it heavier? Geoscientists speculated that lighter elements such as oxygen or silicon might have been present. The abundance of sulfur, another relatively light element, explained the conundrum.

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          The crust is the hard, outer layer of the Earth that forms the land and the ocean floor. The continental crust (the lane masses) is the oldest and thickest part and made up mostly of silica and aluminium. The oceanic crust, made up mostly of silica and magnesium, is around 200 million years old.

          Early on in Earth’s history, minerals began to form. Lighter minerals floated up toward the surface and formed a thin crust of rock around the outside of the planet (which we now live on top of). If Earth was the size of a plum, the rocky crust would be a bit like the thin purple skin. If we want to see below the surface, we can drill down into the crust for thousands of meters.

          The crust is mostly made of minerals such as quartz, feldspar and mica. These are the shiny crystals in granite rocks, which you can see in the southwest of Kenya. Over long periods of time these minerals break down into small pieces and are carried around by winds, currents and waves to form soft sediments like sand. Look out for sediments when you are by a river, a lake or a beach.

          The crust is made up of huge blocks of rock that move around the Earth’s surface very slowly – as slowly as your fingernails grow. The movement of these plates over millions of years causes continents to split apart and smash together. Right now, East Africa is splitting into two pieces along the Great Rift Valley and one day in the distant future, the rift may be flooded by the sea.

          In between the core and the crust is a hot, squishy body of rock called the mantle. The mantle is mostly made of a mineral called olivine, which is a beautiful shade of green. The hot mantle has currents that flow like treacle. These slow currents push the plates of rock around at the surface.

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          The surface of the Earth, the crust, makes up a very small part of the whole planet. While it is relatively straightforward to find out about the Earth’s surface, investigating deep within the Earth is part science, part guesswork. What is known is that there are three main layers: the crust, the mantle and the core, and that these consist of rocks and metals in various states and forms.

          The Earth started out as a ball of very, very hot liquid. This liquid was mostly made of two elements called oxygen and silica. But there were small amounts of other elements too. In fact, it was a mixture of almost every element in existence. This all happened around 4.6 billion years ago – that’s a really long time, so long that we can’t even imagine it.

          Over time, Earth began to cool down. The heavier elements, like iron and nickel, sank into the centre of the planet (the core). And it’s hot: the Earth’s core is as hot as the surface of the sun, so hot that we wouldn’t be able to go near it, let alone touch it. But you don’t have to worry about getting too close. Wherever you are, whether in Kenya, China or Brazil, the core is around 1800 miles below your feet. This means we will never be able to visit it.

          Even though we can’t actually go to the Earth’s core, we know some things about it. We know, for example, that the core is full of iron, because Earth acts like a giant magnet, drawing some elements to it. This magnetic core is very useful: it means we can use a compass to find our way, like sailors in the ocean.

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          The rotation of the Earth causes it to bulge slightly in the middle. Centrifugal force makes the Earth’s material move away from the centre — the faster the spin, the greater the force. As places at the Equator are moving faster than places at the poles, the centre of the Earth pushes out slightly more than the rest.

          The simplest model for the shape of the entire Earth is a sphere. The Earth’s radius is the distance from Earth’s center to its surface, about 6,371 kilometers (3,959 mi). While “radius” normally is a characteristic of perfect spheres, the Earth deviates from spherical by only a third of a percent, sufficiently close to treat it as a sphere in many contexts and justifying the term “the radius of the Earth”.

          The concept of a spherical Earth dates back to around the 6th century BC, but remained a matter of philosophical speculation until the 3rd century BC. The first scientific estimation of the radius of the Earth was given by Eratosthenes about 240 BC, with estimates of the accuracy of Eratosthenes’s measurement ranging from 2% to 15%.

          The Earth is only approximately spherical, so no single value serves as its natural radius. Distances from points on the surface to the center range from 6,353 km to 6,384 km (3,947 – 3,968 mi). Several different ways of modeling the Earth as a sphere each yield a mean radius of 6,371 kilometers (3,959 mi). Regardless of the model, any radius falls between the polar minimum of about 6,357 km and the equatorial maximum of about 6,378 km (3,950 – 3,963 mi). The difference 21 kilometers (13 mi) correspond to the polar radius being approximately 0.3% shorter than the equator radius.

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          The earth spins as a result of things colliding with each other when the Solar System was formed. Some scientists believe that the Earth started spinning after a direct collision with the Moon. Kept moving by the force of momentum, the Earth takes one day to make one full rotation.

          It can’t be a coincidence. Look down on the Earth from above, and you’d see that it’s turning in a counter-clockwise direction. Same with the Sun, Mars and most of the planets.

          It’s the conservation of angular momentum. Think about the individual atoms in the cloud of hydrogen. Each particle has its own momentum as it drifts through the void. As these atoms glom onto one another with gravity, they need to average out their momentum. It might be possible to average out perfectly to zero, but it’s really unlikely.

          Which means, there will be some left over. Like a figure skater pulling in her arms to spin more rapidly, the collapsing proto-Solar System with its averaged out particle momentum began to spin faster and faster. As the Solar System spun more rapidly, it flattened out into a disk with a bulge in the middle. We see this same structure throughout the Universe: the shape of galaxies, around rapidly spinning black holes, and we even see it in pizza restaurants.

          Over the course of a few hundred million years, all of the material in the Solar System gathered together into planets, asteroids, moons and comets. Then the powerful radiation and solar winds from the young Sun cleared out everything that was left over. Without any unbalanced forces acting on them, the inertia of the Sun and the planets have kept them spinning for billions of years.

          And they’ll continue to do so until they collide with some object, billions or even trillions of years in the future. The Earth spins because it formed in the accretion disk of a cloud of hydrogen that collapsed down from mutual gravity and needed to conserve its angular momentum. It continues to spin because of inertia.

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