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Preparation
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It is very likely that any organism on Earth will be either eaten by scavengers or decomposed by microorganisms after it dies. Organisms decompose more quickly when they are in contact with oxygen. Most environments exposed to the open air are in contact with plenty of oxygen, so the soft tissues of dead organisms, whether plants or animals, decay quickly. Many, if not most, underwater environments also have a lot of oxygen, since water can dissolve oxygen from the atmosphere. For an organism to become a fossil, it must not decompose or be eaten. This can happen if the organism either lives within or is moved to a place where it can be buried and kept from decaying. When an organism is buried quickly, there is less decay and the better the chance for it to be preserved. The hard parts of organisms, such as bones, shells, and teeth have a better chance of becoming fossils than do softer parts. One reason for this is that scavengers generally do not eat these parts. Hard parts also decay more slowly than soft parts, giving more time for them to be buried. In this investigation, students think about what it takes for a plant or animal to become a fossil. Students explore decomposition by studying fresh fruit and decomposing fruit. They test the ability of different materials such as sand, soil, and plaster of Paris to preserve pieces of banana. They observe that the finer the material and the more the banana pieces are cut off from the air, the more the banana is preserved.
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For the class:
Per group:
Images to be viewed by the class: For the instructor:
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Remind students not to eat any food used in the investigation. Use disposable craft sticks for mixing the Plaster of Paris and do not let the students do the mixing. 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. Review the investigation for your specific setting, materials, students, and conventional safety precautions. |
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