Coming down to the ground we see that there are layers similar to the atmospheric ones. As we move down from the surface to the interior we come across four distinct layers. These are: the crust, the mantle, the outer and inner core.
Being basically rocky, together these layers are called lithosphere.
The crust, that is the back of the surface, is the outermost part on which our continents and ocean basins rest. It extends only 10 to 30 miles below the ground that we call the surface. The crust is the thickest at the continental region. And the thinnest in the oceans. Lithosphere is thickest in the continental regions and thinnest in the oceans. The average thickness at the continental regions is about 40 Km and that at the ocean bed range from 10 to 12 Km. It is
made of low density rocks, similar to those found on the surface.
Then comes the mantle. It is around 1800 miles thick and extends nearly half way to the center of the Earth. It is made of denser rock. At the bottom of the mantle the rocks are even more denser. This is because it is compressed by the weight of the hundreds of miles of rock above. All the rocks have been formed from molten magma or lava that erupted, through the mouths of the volcanoes, from deep inside the earth. Powerful earth movements have also heaved up some of the rocks to the top surface. Once at the surface these rocks faces the hazards of weather. And they gradually starts wearing over a span of thousands of years.
The Earth's core is even denser and is probably made of iron. It is at the center of the core, the center of the Earth is located. Compressed by theweight of hundreds of miles of rocks above, this layer is much denser. While the outer core is liquid, the inner core has a slightly higher density and is probably solid. Thus the outer core is mostly made up of magma. The magma at this layer remains in a boiling and fluid state. For, it cannot get a chance to cool down and solidify,because of the very high temperature existing at this layer.
The temperature inside the Earth is much higher than that on the surface. The temperature varies in line with the variation in the layers of lithosphere. Just below the surface, the temperature rises 10-20 degrees Fahrenheit for each 1000 feet of depth. The temperature rises more slowly in the mantle, until in the core where it may reach 10,000 to 15,000 degrees Fahrenheit!
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