Earth’s Internal Forces

How Earth is Shaped Internal and external forces both shape the Earth’s surface. The Earth’s internal and external structure, including the tectonic plates, is responsible for the creation of continents, mountain ranges, volcanoes, etc.

Defining Internal & External Forces Internal processes take place within/inside the earth’s surface. For example: plate tectonics, volcanic formations, earthquakes, etc. External processes take place outside the earth’s surface. For example: floods, avalanches, tornadoes, etc.

Earth’s Structure Many scientists believe that most of the landmasses forming our present-day continents were once part of one gigantic supercontinent called Pangaea. Due to continental drift, they slowly separated. Due to plate tectonics, the physical features of the planet are constantly changing.

Wegener’s Theory of Continental Drift http://www.youtube.com/watch?v=QL7LX5-ytOg

Earth’s Layers The Earth is composed of three main layers: The core Inner and outer core The mantle The crust The crust and upper mantle http://www.youtube.com/watch?v=bgnn096PfWQ

Explanation of Earth’s Plates The earth's crust is not a solid shell; it is broken up into huge, thick plates that drift atop the soft, underlying mantle. The plates drift all over the globe; they move both horizontally (sideways) and vertically (up and down). Over long periods of time, the plates also change in size as their margins are added to, are crushed together, or pushed back into the earth's mantle.

The Earth as A Cracked Egg Think of the earth’s crust as a cracked or fractured egg that is composed of many parts that form the entire shell.

The Earth’s Plates

Plate Tectonics Plate tectonics is the movement of earth’s plates. Plate tectonics is responsible for the folding, lifting, bending, and breaking parts of the Earth’s surface. As the plates converge or diverge they create landforms. http://www.youtube.com/watch?v=1-HwPR_4mP4

Subduction When two plates converge the heavier goes under the lighter. The process of two plates converging is called subduction. A trench is the deep valley that forms as a result of subduction During subduction the submerged plate grinds against the plate above it and heat is generated often causing a row of volcanoes. When these volcanoes raise to the surface we call them island chains.

Folds & Faults Moving plates that become compressed or smashed are called folds. Moving plates that slide or move apart from each other are called faults. A fault line is where two plates meet. Also called a plate boundary. Earthquakes occur typically along fault lines. Tension builds up along fault lines as the plates grind against one another. This grinding causes sudden vibrations that we call earthquakes.

How Mountains are formed http://www.history.com/topics/himalayas/videos - mountain-building http://www.youtube.com/watch?v=goszsQl0Bc0

Review What is an internal force and provide three examples? What is plate tectonics and what are three reasons that it is important? What are the three layers of earth and which is made of iron? In your own words define subduction and then draw an image to represent what the process looks like.

External Forces Weathering is when rocks break away or decay over time. The Earth is changed by two basic kinds of weathering: Physical weathering – occurs when large masses of rock are physically broken down into smaller pieces. Chemical weathering- changes the chemical makeup of rocks. For example, rain water that contains carbon dioxide from the air easily dissolves certain rocks, such as limestone.

Types of Erosion Erosion is the movement of surface material from one location to another by water, wind and ice. Wind erosion involves the movement of dust, sand, and soil from one place to another. Plants help protect the land from wind erosion; however, in dry places where people have cut down trees and plants, winds pick up large amounts of soil and blow it away.

Other Types of Erosion Glacial Erosion: as glaciers move, they may destroy forests, carve out valleys, alter courses of rivers, and wear down mountaintops, changing the landscape. Water erosion: it begins when spring water and rainwater flow downhill in streams, cutting into the land, and wearing away the soil and rock.