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Fossils are the preserved remains, or traces, of plants and animals that were buried in sediment. They are typically found in sedimentary rocks.

Body fossils are parts of the living thing itself: bones, teeth, shells, wood or leaves. Trace fossils are signs of what it did: footprints, burrows, nests and coprolites (fossil dung). Trace fossils tell us about behaviour that we could not learn any other way.

To become a fossil, remains must be buried soon after death. Burial protects them from rotting, weathering and scavengers. Hard parts such as shells, bones, teeth and wood last much better than soft tissue. Fossils form more often where sediment is building up, such as in the sea and on river floodplains.

Experiment: Fair test: which 'mud' makes the best fossil?

1. Fill the three pots with dry sand, damp sand and play dough, each smoothed flat.
2. Plan a fair test: what will you keep the same? (Same shell, same pressing force using the book, same time.)
3. Predict which material will keep the clearest print.
4. Press the shell into each material under the book for 10 seconds, then lift it out carefully.
5. Score each mould for detail with the magnifying glass: 0 = no shape, 1 = rough shape, 2 = clear shape, 3 = fine lines visible.
6. Optional: the teacher pours plaster into the best mould. When it has set, lift it out: you have a cast.

Material	Prediction (score 0–3)	Detail score (0–3)	Notes
Dry sand
Damp sand
Play dough / clay

Questions

1. Draw a comic strip with four pictures showing how a sea creature becomes a fossil.

   🍎

2. Which material kept the best fossil print in your test? How did you make it fair?

3. Why are fossils of jellyfish and worms rarer than fossils of shells?

4. A cast is the hollow left by a dissolved shell. True or false?

   true / false

Sources for every fact on this sheet: echoesof.science/school/fossils/sources/

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