Reading Earth's Layers
Lesson 6 of 18
Objective: SWBAT interpret relative time of geological layers using a model.
I prepared 3 different cups with "core samples" before the lesson. You could use any material you wanted, as long as you made the key match. My cups were set up as follows:
Flour, then coffee, then oatmeal
Cornmeal, then flaxseed mixed with marshmallows
Flaxseed mixed with sunflower seeds, cornmeal mixed with marshmallows
To begin the lesson I showed one tables' soil sample jar from earlier in the week that had settled into layers. I explained that if we just left this setting out, in a few million years, each component of the soil would gradually turn into a layer of sedimentary rock. I gave a quick lesson/review that sediment is the particles floating around in the water, perhaps carried away from erosion. I had students add this word and definition to their science notebooks.
I asked which particles settled first, and each table said it was the sand. I asked why, and they said it was the biggest. I explained that since that always was true, geologists could look at those layers to learn about what the history of earth. They know that whatever is on the bottom is the oldest, and the layers get newer as you get closer to the top.
I had planned on showing The Grand Canyon: Evidence of Earth's Past because it gives a sense of scale, both size and time, as well as connecting our learning to the real world, but my students were very inquisitive, so I just asked them to remember a time when they had been on a road trip, and the road cut through a mountain, and we talked about layers.
Last, I explained that geologists can't just cut into every mountain to find out what the history of the earth was there, but they can take core samples by drilling into the earth with a hollow drill bit and pulling out cylinders of rock to examine.
I told my students that I actually brought in some core samples for them today, but they needed to know how to read them. I passed out the Reading Earth’s Layers Key, and told them to read through it, and ask their table if there were any words they didn't know. I took just a minute or two to explain any vocabulary words they still didn't know, then passed out the Reading Earth's Layers questions.
I asked them not to touch or disturb the core samples, and passed out one to each table. I told them they had 8 minutes per sample, then we would be rotating. For awhile I had to just go table to table, having the same conversation-
What's the oldest layer?
Okay, look on the key. Is there a rock called "seeds"?
Than look at the properties and find a rock that matches that description. What color is it?
The other challenge was to get them to use the evidence from the sample, not conjecture. They were trying to come to conclusions about whether sea animals would be near granite (and perhaps my layers weren't plausible) but I kept having them return to the sample. "What evidence from this sample supports your idea?"
I had students just turn in their papers when they were done with the 3rd cup, but they didn't do very well on the 3rd question for each cup. What I would do next time would be to gather them up at the rug, and go over each layer of each cup together. I'd have each student discuss their answers with someone from another table, and then ask for students to share with the class. During the class discussion, I would encourage each person to respond to the person before them, and continually refer back to the key. I would be able to clarify each question if needed, and give them time to revise their answers before turning their papers in.