Earth's Interior (Encyclopedia of Science)
The distance from Earth's surface to its center is about 3,975 miles (6,395 kilometers). Scientists have divided the interior of Earth into various layers, based on their composition. The crust, or outer portion, varies in depth from 5 to 25 miles (8 to 40 kilometers). Below the crust is the mantle, which extends to a depth of about 1,800 miles (2,900 kilometers). Below that is the core, composed of a liquid outer core about 1,380 miles (2,200 kilometers) in depth, and a solid inner core about 780 miles (1,300 kilometers) deep.
From direct observation, core samples, and drilling projects, scientists have been able to study the rock layers near the planet's surface. However, this knowledge is limited. The deepest drill hole, just over 9 miles (15 kilometers) in depth, penetrates only about 0.2 percent of the distance to Earth's center.
Geologists collect information about Earth's remote interior from several different sources. Some rocks found at Earth's surface originate deep in Earth's crust and mantle. Meteorites that fall to the planet are also believed to be representative of the rocks of Earth's mantle and core. Meteor fragments presumably came from the interior of shattered extraterrestrial bodies within our solar system. It is likely that the composition of the core of our own planet is very similar to the composition of these extraterrestrial travelers....
(The entire section is 989 words.)
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