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The Earth’s structure is divided into four parts: the crust, mantle, outer core, and inner core. The crust is solid and makes up less than 1% of the Earth’s volume. The mantle is a plastic solid that flows slowly, creating convective currents. The outer core is molten and generates the Earth’s magnetic field, while the inner core is solid and has high temperatures.
The Earth’s structure is layered and commonly divided into four parts: the silicate crust, the viscous mantle, the liquid iron-nickel outer core, and the solid iron-nickel inner core. Occasionally, the mantle is further subdivided into the inner and outer mantle, based on differences in rock type, temperature, density, and viscosity. The crust, which is the only part of the Earth that is relatively cold and completely solid, makes up less than 1% of its total volume.
The first part of the Earth’s structure, the crust, is made up of cooled rock floating on top of the viscous mantle. The thickness of the crust varies mainly depending on whether it is oceanic (5 km (3 mi) to 10 km (6 mi) thick) or continental (30 km (20 mi) to 50 km (30 mi) thick). Oceanic crust is made up of dense rocks such as gabbro, basalt and diabase, while continental crust is made up of slightly lighter rocks such as granite. The deepest hole ever dug by humans in the crust is 11.26 km (7.62 mi), about a third of the way into the mantle.
Under the crust is the mantle, the most superficial part of which is made up of rocks such as olivine, pyroxenes, spinel and garnet, while the deeper parts are made up of high-pressure polymorphic minerals with elemental composition similar to that of the rock above. The mantle is a plastic solid that flows slowly over the millennia, creating convective currents similar to those observed when pasta is placed in boiling water, only at much slower speeds. These convection currents can create volcanic hot spots and cause continental drift. The mantle is the thickest part of the Earth’s structure, approximately 2,890 km (1,800 miles) thick and makes up 70% of the Earth’s volume. Scientists have learned a lot about the mantle by studying how it effects seismic waves that pass through it.
The most central parts of the Earth’s structure are the outer and inner mantle. The outer core is made of molten iron and nickel. At this depth the temperature is sufficient to melt iron and nickel, but the pressure is not sufficient to force it to solidify. The outer core contains the vast majority of the planet’s iron and nickel, which sank into the core when Earth was in the process of forming about 4.6 billion years ago. Eddy currents in the outer core are believed to generate the Earth’s magnetic field. The inner core has a similar composition to the inner core, but the pressure is sufficient to make it solid. Temperatures in the inner core can exceed those on the surface of the Sun.
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