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Preparation
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In the last investigation, students learned about body fossils, fossils that are the actual organism or some part of it or the imprint of the organism or some part of it. In this investigation, students examine trace fossils, which are physical evidence of the life activities of now vanished organisms. Trace fossils include tracks, trails, burrows, feeding marks, and resting marks. For example, a trace fossil is the trail left behind by an ancient reptile that dragged its tail in mud. Another example is the footprints left by dinosaurs along an ancient river or the hollow tubes created by worms burrowing in soft mud in an ancient ocean. There are more trace fossils than body fossils because one organism can leave behind many traces (e.g. footprints), but only one set of hard parts (e.g. bones) to become a fossil. Most trace fossils were formed in soft mud or sand near a pond, lake, river, or beach. The imprints left by the organisms were quickly covered by sediment. The sediment dried and hardened before the imprints could be erased by water or wind. The sediment was then buried under more sediment and became compacted and cemented together to form rock. This process is much the same as the formation of body fossils. In this investigation, students model the formation of a trace fossil. Using Plaster of Paris and small plastic dinosaurs, they make a series of dinosaur foot tracks (forming a mold). After the Plaster of Paris has dried, they paint it to look more realistic. They cover it with non-stick cooking spray and then with a new layer of plaster (forming a cast). After the new layer has dried, groups exchange their plaster pieces. They split the two sections apart and examine the fossil footprints inside. They examine the footprints for information about what the dinosaurs that created them were like.
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Per group:
Images to be viewed by the class: For the instructor:
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Use disposable craft sticks for mixing the Plaster of Paris. Be sure that you, and not your students, mix the Plaster of Paris. Do not pour unused portions of Plaster of Pairs, or water mixed with Plaster of Paris into the sink or drain. Dispose of them in the trash instead. Students should wear safety impact goggles when cracking the Plaster of Paris. Review the investigation for your specific setting, materials, students, and conventional safety precautions. |
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