Section 2: Forces of Change

A Geographic View

A Planet in Motion

Scientists now know that the earth is very complicated, there is more than a dozen huge plates at the earth's surface. These plates move at very slow pace slower than a snails pace, only inches a year but over millions of years they cover thousands of mile. As these plates collide and separate, they change the globe by deforming features. The earth consists of layers that propel the plates to move very slow.

Earth's Structure

Some forces that change the earth's surface are wind, water, volcanic eruptions, and earthquakes. The earth is composed of three layers- the core, the mantle, and the crust. At the very center of the planet is a very hot but solid inner core. Surrounding the inner core is an outer core about 1400 miles thick. Next to the outer core a thick layer of hot rock called the mantle. The outer layer is the crust a layer that forms the earth's surface. Many scientists believe that the continents today were once part of a gigantic super continent called Pangaea. Over millions of years it has broken into smaller smaller continents, the continents drifted then the theory about them drifting apart is called continental drift. Scientists refer to parts of the crust that slowly move to surface the earth, plate tectonics.

Internal Forces of Change

Internal forces associating with plate tectonics. There are many internal forces, one forces relates with the slow movement of magma in the earth.

Mountains are formed in different ways, some are formed when continental plates collide and some are formed when a sea plate collides with a continental plates. There is a process called subduction where the heavier sea plate dives beneath the continental sea plate. In another process, earth's crust come together slowly as the sea plate with is called accretion.

Sea plates pull apart which is the process called spreading. Some plates squeeze the earth's surface this causes folds or bends.

External Forces of Change

Weathering is a process that breaks down rocks on the earth. Erosion is a process that takes away earths surface by wind, glaciers, and moving water.There is also wind erosion glacial erosion and water erosion.