Chapter 12 Lesson 1, "Weathering"
Materials:
Objective:
Anticipatory Set:* Show the students a bowl of sand and a piece of sandstone. Ask the students what the two have in common? Can one be changed into the other? Remind the students of the rock cycle. Tell them that in this chapter we will concentrate on how the rocks can be broken down into smaller pieces both naturally and by human means.
Teacher Input:* Show the students the picture from page 280 in their book of the tomb stones. Ask them how come the stones are not as polished white as they were when they were first created? 10,000 years from now can we expect them to look just like they do in this picture? Why not? What is the breaking down of rocks on the earth's surface known as? Define weathering and students put it in their notes. Have them write the other vocabulary terms from this lesson in their notes and define them as we come to them:Mechanical weathering, Chemical weathering, oxidation, soil, topsoil, and subsoil.
There are two major ways that weathering occurs. They are both seen occurring in this picture of broken rocks. One is the breaking apart of rocks without changing their mineral composition and the other is breaking apart of rocks caused by a change in their chemical makeup. What are these two types of weathering called Both examples again. Show the students the picture of mechanical weathering from page 280. Explain what is happening in the picture. Another type of mechanical weathering may be when one rock hits against another. In this case small sand grains thrown by the wind have carved these rocks. Another mechanical weathering can take place by roots from trees. here you see how a root can lift a sidewalk just like it will crack a rock. In some cases mechanical weathering can occur if water slips into small cracks in rock then freezes and makes the crack larger such as in this case.
In chemical weathering the rock is actually changed into something else. Sometimes the simple case of rusting can cause weathering in rocks high in iron like on Page 281. The oxygen in the air combines with the iron and forms iron oxide a softer substance that can be broken off by raindrops, wind, or sand being blown around. Some times it may be an acid in the air that breaks down rock like this marble temple. Chemicals are not always found in the atmosphere. In some cases plants or bacteria or lichens may secrete an acid that will break down a rock releasing the minerals for a lichen to use. In some cases water may dissolve the rock. For example feldspar which is found in many rocks can be broken down into clay by water. When the water removes the feldspar then the rest of the rock can fall apart. Limestone can also be broken down by rainwater which is slightly acidic. The acidic rainwater leaves caves in limestone bedrock. Here is the picture of this from the book.
After rocks break down the tiny pieces may form soil. The soil is made up of many more items than just the small particles. Show this soil composition. The soil then forms several different layers the top layer is made of a lot of organic matter and great amount of oxygen and water can be held there. The second layer contains a lot of the iron oxide. That is why it is brown in color. Then near the bottom is the rock particles and solid rock.
Guided Practice:* Students will take turns answering the questions on Page 283.
Independent Practice:* Students will complete the worksheet, Weathering
Check for Understanding:* Students will take the quiz on lesson 1, "Weathering"
Duration:
30 minutes + 10-15 for Independent Practice (Could be longer if taken for homework).
Alaska Content Standards Addressed in this lesson:
