Year 3 Science: How fossils form in layers
Part of the Year 3 Science rocks, fossils and soils chapter. Chapter overview · whole chapter on one page
How fossils form in layers
Most fossils form in layers. Here are the four stages of how a fossil forms. The pictures are not in order.
| Stage | What happens |
|---|---|
| A | A living thing dies and sinks to the bottom of a lake or the sea. |
| B | Sand and mud cover it, and it is buried. |
| C | More layers build up over a very long time. The lower layers are squashed and stuck together into rock. |
| D | Wind and rain wear the rock away, and the fossil is found. |
Sand and mud that settle in layers are called sediment. New layers build up on top of older layers. A layer is one flat band of rock. In layers that have not been turned over, the bottom layer is the oldest, and the top layer is the newest.
Key ideas
- Fossils form when remains are buried in sediment, such as sand or mud.
- Layers build up over a very long time, and the lower layers are squashed into rock.
- In layers that have not been turned over, the lowest layer is the oldest.
- A fossil can be found when the rock above it is worn away.
Method. Find the lowest layer.
- Look at the layers. Layer 1 is at the top, and layer 5 is at the bottom.bottom
- Choose the oldest. The bottom layer is the oldest, so it is layer 5.5
- Write the answer. 5
Check. Layer 1 is the newest. ✓
Watch out. Oldest means it formed first. The bottom layer was laid down first.
Method. Find the top layer.
- Look at the layers. The top layer is the newest layer.top
- Write the number. The top layer is layer 1.1
- Write the answer. 1
Check. Layer 5 is the oldest. ✓
Method. Read the stages in the table.
- Read stage A. A living thing dies and sinks to the bottom, so this is the first stage.A
- Write the answer. So the first stage is A.A
- Write the answer. A
Check. Stage B is the next stage: sand and mud cover the remains. ✓
Watch out
Watch out: the top layer is the newest, not the oldest. The oldest layers are at the bottom, if the layers have not been turned over.
Try it at home or school (with a grown-up). With a grown-up, put layers of different coloured sand, or dry rice, in a clear cup. Add one layer at a time, and press it gently before you add the next. Put a small plastic shell in one layer, and cover it with more layers. Talk about which layer would be the oldest. Wash your hands afterwards.
Exam tip
Grown-up tip. Ask: “Which layer did we add first? Which layer is the oldest?” Let your child explain how the layers build up, step by step.
Exercise 7F How fossils form in layers
Method. Find the bottom layer.
- Look at the diagram. The bottom layer is layer 5.layer 5
- Name the oldest. So layer 5 is the oldest.5
- Write the answer. 5
Check. The bottom layer was the first to form. ✓
Method. Find the top layer.
- Look at the diagram. The top layer is layer 1.layer 1
- Write the answer. 1
Check. The newest layer is on the top. ✓
Method. Look for the shell in the diagram.
- Look for the shell. The fossil shell is in layer 4.layer 4
- Write the answer. 4
Check. Layer 4 is above layer 5. ✓
Method. Look at where each layer is.
- Find the layers. Layer 4 is lower down than layer 2.lower
- Decide. A lower layer is older, so layer 4 is older.older
- Write the answer. older
Check. Layer 2 is newer than layer 4. ✓
Method. Read the text in this section.
- Read the text. Sand and mud that settle in layers are called sediment.sediment
- Write the answer. sediment
Check. Sediment buries the remains of the living thing. ✓
Method. Use the table of stages, and the four pictures.
- Stage A. A living thing dies and sinks to the bottom.A
- Stage B. Sand and mud cover it, and it is buried.B
- Stage C. More layers build up, and the lower layers become rock.C
- Stage D. Wind and rain wear the rock away, and the fossil is found.D
- Write the answer. A, B, C, D
Check. The first stage is A, and the last is D. ✓
Method. Read the table of stages.
- Read the table. Stage D says wind and rain wear the rock away, and the fossil is found.D
- Write the answer. D
Check. Stage C is when the layers become rock. ✓
Method. Read the table of stages.
- Read the table. Stage A says a living thing dies and sinks to the bottom.A
- Write the answer. A
Check. Stage B is when sand and mud cover it. ✓
Method. Think about how layers build up.
- Think about the layers. New layers build up on top of older layers.on top
- Decide. So the top layer is the newest, and Ruby is not right.no
- Write the answer. no
Check. The bottom layer is the oldest. ✓
Method. Think about stage C in the table.
- Think about the layers. More layers build up, and the lower layers are squashed.squashed
- Make the prediction. So the lower layers will be squashed and turn into rock.turn into rock
- Write the answer. Accept any prediction that says the lower layers will be squashed and turn into rock.
Check. Stage C describes this. ✓
Method. Think about how the layers build up in real life.
- Think about the layers. Layers build up one at a time, with the newest on top.one at a time
- Write the step. Add one layer, let it settle, then add the next layer.add one layer
- Write the answer. Accept any step that adds one layer at a time, and lets each layer settle before the next.
Check. A model shows the order of the layers. ✓
Method. Think about what would happen to an animal left out in the open.
- Think about the remains. Remains left in the open can be eaten or rot away.eaten or rot
- Give the reason. Burial in sand or mud protects the remains, so they can turn into a fossil.protects
- Write the answer. Accept any sentence that says the sand or mud covers the remains, which protects them from being eaten or rotting away.
Check. Protection by sand or mud gives a fossil a chance to form. ✓