By Crystal Mason
The crust is a very thin layer of earth when compared to the other layers. It is only five to twenty-five miles thick on. a continental plate and three to five miles on an ocean plate. The crust is divided into twelve plates that float on the mantle. The temperature varies at the surface of the crust along with air temperature but at the bottom of the crust the temperature can reach 1,600 degrees Fahrenheit.
The earth’s crust is made of twelve plates. These plates float around on the mantle’s flowing rock. Sometimes, the plates get caught on the mantle and they build pressure. When the plate builds so much pressure that the rock breaks an earthquake occurs.
The Mohorovicic Discontinuity is the boundary between the crust and the mantle. It is named after Andrija Mohorovicic who in 1909 discovered that earthquake waves near the surface of the earth moved slower than those that passed through the interior of the earth. Mohorovicic stated that this was because the crust of the earth is made up of less dense material and the mantle is much more dense than the crust. Since the mantle is much more dense the waves move faster through the mantle rock.
The mantle is the thickest layer of the earth. It is 1,800 miles thick. It is made up of very hot and dense rock under the weight of the crust. The temperature varies from 1,600 degrees at the top to 4,000 degrees at the bottom. The rock moves around because of convection currents.
Beno Gutenberg claimed that the outer core of the earth was made up of liquid because secondary waves could not pass through it and were sometimes bounced off. The boundary between the mantle and the outer core is called the Gutenberg Discontinuity to honor his discovery.
The outer core is about 1,400 miles thick. The temperature ranges from 4,000 to 9,000 degrees. It is composed of melted nickel and iron.
The inner core is also made up of iron and nickel. The metal are under 45,000,000 pounds of pressure per square inch. Under this great amount of pressure the metal becomes a solid even though the temperature can reach up to 9,000 degrees. The pressure of the core is three million times that of the air pressure at sea level on the earths surface.
An apple can be used visually to describe the layers of the earth. The skin of the apple is like the crust of the earth. The middle soft part is used to describe the mantle. The outer edge of the apple core is like the outer core of the earth and the inner part of the apple core is like the inner core of the earth.
Earth Diagram Worksheet
Outer Layers of the Earth Worksheet