1. Constructive Forces and the Earth’s Layers
Mrs. Daugherty

2. Building up Earth’s surface
Deposition is the dropping, or releasing, or sediments that have been moved from one place to another.
Deposition is a constructive force because it builds up land – such as a sand dune that is built due to sand being moved from one place to another.
These specks are people!
Check out how these sand dunes were formed through deposition -

3. How does deposition work?
What do you notice about the source of the rivers?

4. How does deposition work?
As water flows down hill, it flows quickly.
As it is going downstream the water picks up sediments.
Because the water is moving quickly the water carries the sediment along with the river.
As the river nears the mouth, the land usually flattens out.
As the land flattens out the water slows down.
When the water slows down the sediments are able to drop to the bottom and sides of the river.

5. How does deposition work?
When the flow of the river slows quickly, special kinds of deposits are formed call alluvial fans. Alluvial fans are fan-shaped land masses that form after and river rushes down a steep slope and then slows abruptly.

6. How does deposition work?
A delta is a low plan that forms where a river enters an ocean. It the river is large the delta will be lard. The Mississippi River has a delta that extends well out into the Gulf of Mexico.

7. How is the earth like an apple?
Like an apple the earth has a skin called the crust, a fruit called the mantle and a core

8. The Layers of the earth Mantle Outer Core Crust Inner Core
Click here to learn about the inside of the earth

9. The Crust We live on the crust!
The crust is the outer layer of the earth. It is also the thinnest layer. The crust is made mostly of granite and basalt which contains elements such as silicon, potassium, aluminum, magnesium, calcium and iron.
Continental crust forms the earth’s landmasses and is about 35 Km thick.
Oceanic crust is found below the earth’s oceans and is about 8 Km’s thick.
Click here to watch a video about the earth’s crust.

10. The Mantle
Click here to see a video about the mantle
The middle layer of the Earth is called the mantle. The mantle is the thickest layer of the earth. The mantle is solid rock. The solid upper mantle and crust combine to form a rigid shell called the lithosphere.
Below the lithosphere much of the rock material in the mantle is partially melted. The solid lithosphere can be thought of as floating on this thick lower mantle.

11. The Core
The core is the center layer of the earth. It is the hottest layer and is divided into two sections – the inner core and the outer core.
The outer core is thick and is the only layer that is in a liquid state.
The inner core is solid iron. The intense pressure in the inner core keeps the metal from melting.
Click here to see a movie about the core.

12. Pushing up the Earth’s surface
Magma – creates new surfaces
How do forces work together to CONSTRUCT new surfaces?
What is Magma?
Melted rock below the Earth’s surface.
Pressure below the surface can cause magma to push up on the Earth’s crust, creating round, dome shaped mountains.
Magma can also come through the Earth’s surface as lava. As the lava flows it cools and hardens into rock, creating new land masses.
One way new surfaces are constructed is through deposition.
Another way new surfaces are created is from below the Earth’s surface.

13. Shield Cones
Shield cones are where lava has built up to form a huge deposit with gently sloping sides.
Most shield cones form on the ocean floor.
The Hawaiian Islands are actually the tops of giant shield cones. (Is that a constructive force?)

14. Building up the Earth’s surface
Mountains are built when one of the plates of the Earth’s crust crashes into another plate.
After the plates crash, the crust folds back on itself forming mountains – much like two cars in an accident. – this process in how the Himalaya Mountains in Asia were formed.

15. Building up the Earth’s surface
Another way the Earth’s surface is built up is through fossil remains.
Shells and skeletons are tiny animals are deposited on the ocean’s floor and built up over time.
The chalk cliffs of Dover, England and The Great Coral Reef are both examples of this type of constructive force.

16. Building up the Earth’s surface
Glacial deposits are another way that the Earth’s surface is built up.
Glaciers formed from the buildup of snow and ice.
As glaciers move and the ice melts, the soils and rock within the glacier are deposited forming new land masses.
The rock material deposited by a glacier is known as till.
Till may be silt, sand, gravel, boulders, or sharp rocks.
Long Island, New York was formed by till. This type of till was called a moraine.
Glaciers scrape away rock to form valleys and cirques. They also deposit rocks, soil, sand, and gravel to build up the land.