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One can imagine a day when humans will venture freely to our neighboring planets, and use powerful telescopes to learn about nearby stars. Someday, we will surely explore every inch of the ocean's depths , as well as all the most impenetrable forests. But we'll probably never journey to the center of the Earth. The hardiest drills penetrate only 7 miles (12 km) deep that's just 0.2 percent of Earth's radius before encountering such high heat that they melt. In all likelihood, the extreme temperature and pressure of our planet's interior place it permanently out of reach.
Perhaps partly for this reason, the inside of the Earth has always fascinated us. It plays a central role in many traditional religions and cosmologies. More recently, science has begun to probe it indirectly, gradually bettering our understanding of its nature. Here is a chronological look at humanity's ever-evolving understanding of the fiery world beneath our feet.
Pit of hellSlide 2 of 13
Pit of hell
Perhaps the most widespread traditional view of the center of the Earth portrays it as a lake of fire where bad people spend eternity: Yes, hell. Connections to the afterlife aside, the picture of the underworld as, essentially, a fiery pit is somewhat accurate. And perhaps it isn't so surprising that so many religions and cosmologies got it right: Volcanic eruptions occasionally provided ancient cultures with horrific glimpses of the hellfire below.
In fact, brimstone as in "fire and brimstone," a frequent metaphor for hell found in the Christian Bible is a type of rock commonly found on the rims of volcanoes.Slide 3 of 13
World turtleSlide 4 of 13
Many East Asian and Native American cultures did not picture the Earth's interior as a hellish place. Instead, they imagined a giant turtle. Called "the world turtle," it supported the Earth usually conceived of as flat , or dome-shaped, rather than spherical on its back. There are several variations to the myth: Hindus replaced the turtle with an elephant, while some historians, perhaps conflating the two descriptions, have described a cosmology where the world rests on the back of an elephant that stands on a turtle.
Why a turtle? As the anthropologist Frank Speck pointed out in a 1931 treatise on the world turtle myth of the Delaware Indians, not only is the creature's back an appropriately curved shape, but the Delaware believed that turtles embody the traits of perseverance, longevity and steadfastness. What's more, they thought that time and turtles alike continuously moved from east to west.
So what's below the turtle? Most myths do not specify. In "A Brief History of Time" (Bantam Dell 1988), the physicist Stephen Hawking recounts a well-known anecdote in which a supporter of the world turtle cosmology is confronted with the question. She answers that the turtle stands on the back of another turtle, which stands on another, and that there are "turtles all the way down."Slide 5 of 13
Core of goldSlide 6 of 13
Core of gold
Bernard Wood, a geologist now at the University of Oxford in the U.K., calculated that there are 1.6 quadrillion tons of gold in the Earth's core, or enough to coat the planet's surface in a 1.5-foot layer. He thinks there is also six times that amount of platinum another precious metal as well as nickel, niobium and other "iron-loving" elements down there. Wood formed this hypothesis after analyzing the metal content of meteorites that are similar to "planetesimals" small bodies that crashed together to form Earth at the dawn of the solar system. He found that these meteorites have much more gold, platinum and the other stuff distributed throughout them than does the surface of the Earth, and deduced that the iron in the Earth's core must have drawn these elements inward during the planet's formation.
The picture above exaggerates: Though 1.6 quadrillion tons is a huge quantity by Earth's-surface-standards, gold atoms still make up just one millionth of the total number of atoms in the core. Meteorites, as well as the mass and density of Earth (deduced from how it perturbs the orbits of the moon and other planets), lead scientists to believe that the vast bulk of the core is iron and nickel.Slide 7 of 13
Onion layersSlide 8 of 13