The earth's mantle roughly extends about 1,798 miles. The density of the mantle changes because of pressure and heat. The further down the mantle is the more pressure and heat we encounter (Nicholls, Bill 1).

The world's lithosphere covers the entire earth (outer shell) and can be broken in many places to form what is called plates. These continental and oceanic plates are constantly moving and they never stop. With the concurrent movement of our lithosphere many mountains, volcanoes, and earthquakes will be created because of these plates (Spall, Henry 1).

also cause earthquakes. Although it seems odd we encounter earthquakes, under water they still occur. Small narrow ridges within the seafloor are cracking because the crust is in constant motion, and with constant motion the oceanic crust is breaking away. Volcanic eruptions from the earth's mantle will eventually fill these cracks and form a replaceable crust (Spall, Henry 1).

Earthquakes are characterized into three classes "'Shallow, less than 20 miles down; Deep, down to the mantle boundary at 50-60 miles; and very deep, in the upper mantle from 60 to about 400 miles'" (Nicholls, Bill 3). The shallow and deep portions of the continental plates determine how strong and powerful earthquakes can become.

In our world we have what is called major crustal plates "'we now know that there are seven major crystal plates, subdivided into a number of smaller plates'" (Spall, Henry 2). The small plates are above 80 kilometers thick. All of the seven crustal ar

Some common words found in the essay are:
Nicholls Bill, Spall Henry, , spall henry, nicholls bill, spall henry 2, henry 2, continental plates, nicholls bill 3, earth's crust, constant motion, earth's mantle, bill 3, oceanic plates, henry 1, spall henry 1,
Approximate Word count = 649
Approximate Pages = 3 (250 words per page double spaced)