1. Weathering, Erosion, and Deposition
How is the surface of the earth formed?
Vocabulary Study

2. Warm Up:
1. Name two types of mechanical weathering.
2. Name two types of chemical weathering.

3. Weathering
When we describe something as “weathered,” we mean it is kind of worn out.

4. Even people can look or feel “weathered
Even people can look or feel “weathered.” In this case, it just means they are very tired because of something.
It’s all this schoolwork.
It’s really
breaking me down!
Psst! Hey buddy! You’re looking a little “weathered.” What’s wrong?

5. We might feel broken down and weathered by work, but in Earth science… weathering is the process through which rock material is broken down by physical or chemical activity.

6. There are two types of weathering:
Mechanical and
Chemical

7. Mechanical weathering is the breakdown of rock into smaller pieces using physical forces. Examples are ice, wind, water, gravity…even plants and animals.
Chemical weathering happens because of chemical reactions. There is some sort of change going on. Examples are water, some types of acids, and air.

8. Here is an example of mechanical weathering by a tree
Here is an example of mechanical weathering by a tree. The tree roots are pushing through this rock, causing it to break apart over time.

9. Abrasion is another type of mechanical weathering
Abrasion is another type of mechanical weathering. This happens when two different rocks or earth materials grind or scrape against each other. If you have ever scraped your elbow or knee, we call that an “abrasion.” OUCH!

10. One example of rock abrasion is when sand blows in the desert
One example of rock abrasion is when sand blows in the desert. Over many years, the tiny bits of sand rub against soft rock and wear it down…almost like sandpaper! Hot temperatures also contribute to this.

11. Mechanical weathering also happens when water freezes inside the cracks in rocks. This is called ice wedging. When the water freezes into ice, it expands, pushing against the cracks so the cracks become bigger. Eventually, the rock breaks apart.

12. Water running over rocks can break them down.

13. Animals burrowing in the ground can cause mechanical weathering.

14. Chemical weathering is caused by a chemical reaction, for example, air or oxidation. Some people call this “rust.” You see the red parts? This happens because oxygen and water in the atmosphere mixes with the chemicals of the metal of the car (steel or iron). It ends up red because of the chemicals in the iron. Cars usually start rusting when the paint comes off, because the paint helps protect the metal from the air and water.

15. This rock is red because of the oxidation of iron in the sediment when the rock was being formed.

16. Acid precipitation (rain or snow) also weathers rocks
Acid precipitation (rain or snow) also weathers rocks. The acid will eat away little holes in the rock. Just like if you eat too much candy, sugar can break down and cause cavities in your teeth!

17. Acids in Groundwater
Water in the ground can contain weak acids that can react with rocks in the ground (like limestone). The dissolving of these rocks like limestone over time can form caverns.

18. Acids in Living Things
Lichens can produce acids that can slowly break down rock. You have probably seen lichen growing on the sides of trees or rocks.

19. Question: If you wanted to move a bunch of earth from one location to another, how would you do it?

20. This might be helpful. This machine is called an “earth mover
This might be helpful. This machine is called an “earth mover.” It’s built for one purpose only, to move A LOT of dirt!

21. However, there are other earth movers too: wind, water, ice, and gravity. All of these forces actually MOVE earth materials like rocks, sand, and soil (dirt). Erosion is the process by which wind, water, ice or gravity transports (moves) soil and sediment from one location to another.

22. If you move something, it has to go somewhere, right
If you move something, it has to go somewhere, right? Well, while erosion is the moving of earth, then deposition is when earth material is “put down.” Just look at the word “deposit.” What should you do with money? Deposit (put) it in the bank!

23. See all these rocks and bits of gravel
See all these rocks and bits of gravel? To get here, huge blocks of ice moved them down the mountain. As the ice moved, the rocks got stuck inside. When the ice melted, the rocks stopped moving. The ice had“deposited” (put) the rocks here.

24. The rocks that the ice left are examples of sediment
The rocks that the ice left are examples of sediment. Sediment is small pieces of rocks and minerals. If you have ever walked barefoot in a stream or lake and felt the sand and small rocks between your toes, you were walking on sediment!