Chapter 2 Section 2

Sarah and Brianna

Forces of Change

Scientist have concluded that from available evidence, the center of the earth has intense heat and pressure. Movements deep within the earth drive members of changes that renew the earth's surface.

Earth's Structure

For hundreds of years the surface of the earth has been in slow constant motion. Forces like wind and water occur on the earth's surface. volcanic eruption and earthquake occurred deep inside the earth.

A Layered Planet

At the center of the planet is a hot but solid core and its about 4,000 miles from the surface of the earth. Scientist believe that this core is made up of iron and nickel. A liquid outer core surrounds the solid inner core and is about 1,400 miles thick. Next to the outer core is player of hot dense rock called the mantle, it release 80% of the heat that is generated from the earth. The outer layer is the crust, which is the earth's surface. Over millions of years Pangea (or the gigantic super continent) from 500 million years ago, broke apart into smaller continents. The theory of Pangea breaking apart is called the Continental Drift. When plates spread apart, magma or molten rock rises up and ridges are formed. Scientist use the term to refer to all of the activities such as mountains, volcanoes, and earthquakes. According to some scientist, in millions of years, the movements of tectonic plate will have made the earth look completely different. Movements of plates are extremely slow and difficult to detect.

Internal Forces of Change

Scientists believe that internal forces involve folding, lifting, bending, or breaking the rock. Mountains are formed in areas where giant continental plates are formed. Subduction is when a heavier sea plate goes under a lighter plate. Accretion is when pieces of the earth's crust come together slowly as the sea plates slide under the continental plate. Spreading is when a rift allows lava from inside the earth to come up between the plates. Folds are bends in layers of rock. Faults are cracks in the earth's crust. Faults occur when folded land can't be bent any further.


Earthquakes are sudden violent movements of plates. Earthquakes usually occur where different plates meet one another. During a fire it is a zone of earthquake and volcanic activity. volcanoes are mountains formed by lava that rise through the cracks. Volcanoes arise in areas away from plate boundaries.

External Forces of Change

Weathering breaks down rocks on the earths surface. Erosion is the wearing away of the earth's surface. Physical weathering is when small rocks are broken down. Chemical weathering is when minerals are combined with a new element in the rocks. Wind erosion is movement of dust, sand, and soil. Loess is a fertile yellow soil deposited by wind. Glacier are large bodies of ice that move against the earth's surface. Moraines are large piles of rocks and debree from glaciers that melt. Sheet glaciers are late broad sheets of ice. Mountains glaciers more common than sheet glaciers. They are located in high mountain areas. Fast moving water is the most significant cause of erosion. Ocean waves continually erode coastal cliffs.