Science at key stage 3 (Year 8)
Unit 8G: Rocks and weathering
Section 10: b. Why do sediments form layers?
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Objectives |
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- that sedimentary layers can be formed by the evaporation of waters containing dissolved salts
- that the remains of dead organisms and their shelly material can accumulate to form sediments
- to use evidence in rock layers to suggest a sequence of events over time
- about the use of fossils as evidence
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Activities |
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Outcomes |
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Children: |
- Ask pupils whether water in rivers, lakes, seas has solids dissolved in it. Remind them of earlier work on different types of water. Ask them to explain the origin of the salts. Use a flow diagram to explain how salts become concentrated in seas or lakes. Ask pupils to suggest what would happen if the seawater evaporated and how to test their ideas. Modify the flow diagram to discuss how seas and lakes can dry up.
- Explore with pupils how a sequence of sediments can be built up by covering the residue from evaporated sea water with a layer of clay and shells to represent the remains of dead organisms, adding more seawater and allowing it to evaporate. Extend to the formation of oil,
eg by using video clips.
- Give pupils a simplified diagram showing different strata and ask them to tell the story of how the layers were formed and why fossils are often found in sedimentary layers.
- Extend by asking pupils to use secondary sources to find out about Mary Anning and the fossil specimens she collected.
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- describe how dissolved solids are left behind when water evaporates
- describe a possible sequence of events leading to a pattern of sedimentary strata
- justify their sequence using the evidence from the layers
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Points to note |
- Pupils are likely to have investigated different types of water at key stage 2 to find out whether they contain dissolved solids.
- The use of fossil fuels is included in unit 7I 'Energy resources'.
- Extension: pupils could be asked to find out about how evidence in rock strata,
eg fossils, coal layers, has been used to develop other ideas about changes in the Earth over time,
eg continental drift, climate changes.
- Teachers will be aware of the need to be sensitive to different religious beliefs.
Safety
- care is needed if the seawater is evaporated by heating. Eye protection should be worn
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This unit is divided into sections. Each section contains a sequence of
activities with related objectives and outcomes. You can view this unit by
moving through the sections or print/download the whole unit.
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