Once students have learned what weathering is, by hands-on investigation, it is time to put the precise language into practice. I like to listen to students use their own language to describe what they are observing. It is much more descriptive than using a word they do not have context for. I try to record the words I hear and use them as I define the technical terms in this vocabulary lesson.
In previous lessons we have looked at chemical and physical weathering. Students have observed how these processes occur using demonstrations of chemical and physical weathering. They made observations of what was occurring and then made inferences as to what these processes may be called.
I walked around the room and listened to student conversations. Words such as:
- breaking down
were heard in student conversations. I can now weave these words into the definitions of weathering, chemical weathering, and mechanical weathering.
RAP – Review and Preview
I call students to the gathering area with their observations from the two days of “Buckling and Bending the Earth” lessons. We talk about what they observed. I note any inferences made, but do not challenge them at this time. I note, on a sheet of chart paper, the words students are using that indicate their understanding of the weathering process that are occurring. We will use these, along with my observations, to make our definitions.
At this point, I ask students if they can see differences in the weathering processes that they demonstrated. Students begin to see that although the water and vinegar are both liquids, one is a mechanical weathering process and one is a chemical weathering process. They talk about the differences in reactions of water and vinegar on the rocks. Students discuss the process of the sand grinding on the chalk. Together, I guide them to seeing two different processes at work.
Students begin to ask what these two processes are called and this is when I can begin to teach the terms and their definitions. Students now have a solid foundation of the processes. They have a picture in their minds of what happens, and now they can attach the terms to these processes.
I post three big cards labeled: “Weathering” “Mechanical Weathering” and Chemical Weathering” on the board.
I tell students that in the last few lessons they have used weathering and erosion somewhat interchangeably. I tell them that these terms are related, but are subtly different. Weathering is the breaking down or chemical change in rocks without a movement of the broken particles. Erosion is the movement of weathered particles.
I ask students to go back to their desk groups and to discuss what they think are the differences between the processes they observed, and to categorize them under “mechanical” or “chemical” weathering. Once they have done that, I ask them to try to define each process using the word list we generated together at the beginning of the lesson.
I give students about 5-10 minutes to have this conversation and then to draft a definition.
Students come back to the gathering area, they sit in a circle so that we can discuss their definitions. I choose one group to start. Each group thereafter must use the hand signals to either add information to what was said or to add new information that is pertinent to the discussion.
Together we come up with definitions that are true to the dictionary definitions of the terms, but written in kid-friendly language.
The dictionary definitions are:
Chemical weathering: Chemical weathering is caused by rain-water reacting with the mineral grains in rocks to form new minerals (clays) and soluble salts. These reactions occur particularly when the water is slightly acidic (The Geological Society of London, n.d.)
Mechanical Weathering: Physical weathering is caused by the effects of changing temperature on rocks, causing the rock to break apart. The process is sometimes assisted by water (The Geological Society of London, n.d.)
Students work in their desk groups to draw pictures of the processes of weathering to accompany the class definition.
As we finish defining the terms, I share some pictures with students that show different weathering processes. This helps solidify their understanding of the processes and offers new ideas for pictures and words to add to the class definitions. All of these pieces are put together in a class poster for use during the rest of the unit.