Together, this uppermost part of the mantle layer and the crust are known as the lithosphere. The mantle’s outermost zone is relatively cool and rigid. These crystals are then brought to the surface in volcanic rock known as kimberlite. But rare “super-deep” diamonds may have formed as far down as 700 kilometers (435 miles) below the surface. Most form at depths above 200 kilometers (124 miles). Geologists believe this weak, hot, slippery part of the mantle is what Earth’s tectonic plates ride upon and slide across.ĭiamonds are tiny pieces of the mantle we can actually touch. Indeed, it forms a layer of partially melted rock known as the asthenosphere (As-THEEN-oh-sfeer). Near its upper edges, somewhere between about 100 and 200 kilometers (62 to 124 miles) underground, the mantle’s temperature reaches the melting point of rock. Like the layer below it, this one also circulates. Made mostly of iron, magnesium and silicon, it is dense, hot and semi-solid (think caramel candy). It starts a mere 30 kilometers (18.6 miles) beneath the surface. The mantleĪt close to 3,000 kilometers (1,865 miles) thick, this is Earth’s thickest layer. Scientists are still working to understand how that happens. For reasons somehow related to the outer core, Earth’s magnetic field reverses about every 200,000 to 300,000 years. They, in turn, generate Earth’s magnetic field. That motion generates electrical currents. Heated largely by the radioactive decay of the elements uranium and thorium, this liquid churns in huge, turbulent currents. It sits some 5,180 to 2,880 kilometers (3,220 to 1,790 miles) below the surface. This part of the core is also made from iron and nickel, just in liquid form. It would likely consist almost entirely of iron. Some research suggests there may also be an inner, inner core. Pressures here are immense: well over 3 million times greater than on Earth’s surface. That’s almost as hot as the surface of the sun. It’s also intensely hot: Temperatures sizzle at 5,400° Celsius (9,800° Fahrenheit). The inner core spins a bit faster than the rest of the planet. Extremely dense, it’s made mostly of iron and nickel. It’s located some 6,400 to 5,180 kilometers (4,000 to 3,220 miles) beneath Earth’s surface. This solid metal ball has a radius of 1,220 kilometers (758 miles), or about three-quarters that of the moon. A cut-away of Earth’s layers reveals how thin the crust is when compared to the lower layers. Here’s a primer on Earth’s layers, starting with a journey to the center of the planet. Scientists - including Isaac Newton, three centuries ago - have also learned about the core and mantle from calculations of Earth’s total density, gravitational pull and magnetic field. The speed and behavior of these waves change as they encounter layers of different densities. They’ve plumbed it by studying how earthquake waves travel through the planet. Still, scientists know a great deal about Earth’s inner structure. In fact, the deepest humans have ever drilled is just over 12 kilometers (7.6 miles). Except for the crust, no one has ever explored these layers in person. They are, from deepest to shallowest, the inner core, the outer core, the mantle and the crust. Starting at the center, Earth is composed of four distinct layers. To really understand Earth, you need to travel 6,400 kilometers (3,977 miles) beneath our feet. Yet even the deepest canyon is but a tiny scratch on the planet. Earth’s surface is an amazing place to behold.
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