Basic Geology/Structure and Composition of the Earth

The crust is the outer-most layer of the earth, the layer we live on. There are two kinds of crust: the continental and the oceanic. The continental crust lies beneath land and it varies from 35-70km thick. The oceanic crust lies under seas and oceans (not just any body of water) and ranges from 5-10km thick. Under the crust is a layer called the lithosphere. The lithosphere is made up of giant, puzzle-like pieces of rock called tectonic plates. Continents have their own plates with oceanic plates and minor plates filling in the gaps. The lithosphere floats on a layer of hot magma called the asthenosphere. The asthenosphere has a convection current, made by magma swirling around in a circular motion, from top to bottom. The convection current is what makes the plates move. The asthenosphere is part of a gigantic layer that takes up a full 2/3 of the Earth's radius: the mantle. The asthenosphere is part of the upper mantle, closest to the crust. The upper mantle is made of magma and hot silicon, iron, magnesium, and oxygen. Its texture is a thick, plasticky, fluid: not unlike half-dried glue. The lower mantle is made of the same materials as the upper mantle, but it is solid rock. It extends to 2,900km below the surface of the earth. The Earth's core is divided into two parts: inner and outer. The outer core is Earth's only entirely liquid layer. It is made up of molten iron and nickel and is 2,200km thick. The inner core can be found 5,100km below the surface. It is a hard ball of extremely hot iron. The inner core was created by the pressure of all the outer layers pushing in on it. The inner core is suspended, floating, in the outer core. It spins at a different rate from the rest of the earth and scientists believe that this, along with the convection current in the asthenosphere, creates the magnetic field that surrounds the earth.