Name______
Title: Underlying Assumptions
Introduction: Most of Earth’s history occurred long before people were around to record what happened. However, scientists have theories about what happened thousands and millions of years ago. They base these theories on two assumptions. (an assumption is a statement that is accepted as true and from which a conclusion can be drawn) One is that events in the past occur in the same way as events do now. Or in other words, if we have floods now that deposit sediments on valley floors, they did the same thing in the past. Another assumption is that sedimentary rocks stack up on Earth’s surface with older layers on the bottom. In this activity, you will look at three models of sedimentary layering to help you understand it.
Part I
1)Now that you are “all grown up”, you have stumbled across your old toy box and begin to dig through your past. You retrieve several items and you begin to think of how you have changed all of these years.
2)In the box below, illustrate all of your memorable toys that you can remember with the oldest toys on the bottom. (Try to remember toys from when you were even a baby!) *Note toys do not have to be spatially stacked on top of one another.
3)When you have finished illustrating your toys, draw horizontal lines to section off the following years.
0-2 years 2-5 years 5-8 years 8-12 years
MY TOY BOX
Questions:
1. Where are the oldest toys?
2. What does the type of toys and size of the clothes show about you?
3. Which layer would contain toys and clothes most like the ones you are currently using?
4. If you went downstairs and saw a very old toy on top of the pile in your toy box, what would you assume?
5. Create a timeline for your toy box. Divide it into parts and name them by the dominant toys. Scientists have also done this with time. You may be familiar with the name “Jurassic”. It names a time period that had dinosaurs.
toys
years
6. Now imagine that someone else stumbled across your toy box. As they search through your toy box, how might the items serve as evidence of how you have changed physically and emotionally and matured over time? Explain. List at least 4 changes.
Part II
Paleontologists (scientists that study the past) have constructed diagrams to show what rock layers have formed in different places on Earth. One of the most famous is the Grand Canyon in Arizona. On the next page is a picture of some of the rock layers in the Grand Canyon. Use the diagram to answer the questions.
Questions
9. Which type of rock is youngest?
10 . What inferences do scientists make to determine the relative ages of rock layers?
11. If it were discovered that the Coconino sandstone was younger than the Toroweap formation, what would scientists assume?
12. Fossils found in the Kaibab limestone include brachiopods, coral, mollusks, and sea lilies. How has this part of Earth changed since these fossils were formed?
Conclusion: How have these models helped you understand the assumptions that scientists make about sedimentary rocks on Earth?