Forces of Change

Section 2

Earth's Structure

The earth is made of three layers the core, the mantle, and the crust. The inner core is extremely hot and a solid and the outer core is a liquid and is just as hot. The mantle is a hot dense rock. The outer layer is the crust and it is a rocky layer. The crust contains many tectonic plates. Tectonic plates lay on magma sometimes when they go against one another or towards one another they form mountains or earthquakes. Before there were continents scientist believed that all the continents were all one continent they called this Pangea. Scientist believe that the continents slowly moved apart which made them how they are today they call this continental drift.

Internal Forces of Change

The surface of the earth has changed over time. Some of these changes come from internal forces associated with plate tectonics. Internal forces involve movements that fold,lift,bend or break the rock along earth's crust. In a process called subduction the heaver sea plate dives beneath lighter continental plate. During accretion pieces of the earth's crust come together slowly as the sea plate slides under the continental plate.Sea plates also can pull apart in a process known as spreading. The resulting rift, or deep crack allows magma from within the earth. Becomes molten material then becomes magma then forces volcanic mountains. Accretion- where continental and sea plates meet. Earth's crust come together slowly as sea plate slides under the continental plate. Such as build up can cause continents to grow outward. New land is also created where two sea plates converge.

External Forces of Change

The external forces change the physical appearance of earth and have for many years. Weathering is just one example of an external force, weathering is the process of breaking down rocks and making them smaller. Another example is wind erosion this force carries dust, rocks and sediments and moves them to different areas. Glacial erosion picks up whatever is in its way while its traveling and sometimes of a glacier begins to melt it will leave a big chunk of ice behind that may contain dirt or rocks this is called moraines. Lastly there is water erosion this carries sediment in its fast moving water. When water erosion continues to happen in one place it can create a valley a great example of this is the Grand Canyon.