Fossils and living things over time
By the end of this chapter you will be able to
- Say what a fossil is, and give examples of body fossils and trace fossils
- Describe how a fossil forms, in layers of sediment, over a very long time
- Use the order of layers and the ages of fossils to find which is older
- Explain that some living things have died out, and that living things have changed over time
- Use fossil evidence to support or refute an idea, and say what fossils cannot show
You should already know
- Rocks and soils, including sedimentary rock and how soil is formed (Year 3 Science, Chapter 7)
- Living things and their habitats, and classification (Chapter 2 of this book)
Where this leads
- Offspring, adaptation and evolution by natural selection (Year 6 Science, Chapter 6)
National Curriculum for England, Key Stage 2 science, Year 6. Content: EV1 recognise that living things have changed over time and that fossils provide information about living things that inhabited the Earth millions of years ago.
Exercise P Do you remember?
Method. Think about rock formed from layers.
- Recall the rock. Sedimentary rock is formed when layers of sediment are pressed and cemented together.sedimentary
- Write the answer. sedimentary
Check. Igneous rock forms from cooled magma, and metamorphic rock from heat and pressure. ✓
Method. Think about the word for animals without a backbone.
- Recall the word. Animals without a backbone are called invertebrates.invertebrates
- Write the answer. invertebrates
Check. Vertebrates have a backbone. ✓
Method. Recall the blood vessels.
- Recall. Veins carry blood back to the heart, and have valves.veins
- Write the answer. veins
Check. Arteries carry blood away from the heart. ✓
Method. Recall the process.
- Recall. Plants use light to make food, in a process called photosynthesis.photosynthesis
- Write the answer. photosynthesis
Check. Plants also need water and air. ✓
Method. Recall the word.
- Recall. A material that light cannot pass through is called opaque.opaque
- Write the answer. opaque
Check. A see-through material lets light through. ✓
What fossils are
A fossil is the remains or trace of a living thing that lived long ago, usually many thousands or millions of years ago. Fossils tell us about living things that are no longer alive.
- A body fossil is a part of the living thing itself, such as a bone, a shell or a tooth, that has turned into stone.
- A trace fossil is a sign that a living thing was there, such as a footprint or a burrow.
Hard parts, such as bones and shells, are much more likely to be preserved than soft parts, such as skin or muscle, which decay quickly.
Key ideas
- A fossil is the remains or trace of a living thing that lived long ago.
- A body fossil is a part of the living thing, such as a bone or a shell.
- A trace fossil is a sign of a living thing, such as a footprint.
- Hard parts are more likely to become fossils than soft parts.
Method. Think about what is preserved.
- Look at the fossil. The shell is a part of the living thing itself.part of the animal
- Name the type. A part of the living thing is a body fossil.body fossil
- Write the answer. body fossil
Check. A footprint would be a trace fossil. ✓
Method. Think about the footprint.
- Look at the fossil. A footprint is a sign that a living thing was there, not a part of it.sign
- Name the type. So the footprint is a trace fossil.trace fossil
- Write the answer. trace fossil
Check. A footprint shows the animal walked there. ✓
Method. Think about which part lasts longer.
- Compare the parts. Hard parts, such as bones, last longer than soft skin, which decays quickly.hard parts last
- Choose. So a bone is more likely to become a fossil.bone
- Write the answer. bone
Check. Hard parts are preserved more often. ✓
Watch out
Watch out: a fossil is not a living thing. It is the remains or the trace of one, which has been preserved in rock.
Exam tip
Exam tip. Use the words body fossil or trace fossil, and say what the fossil shows about a living thing from long ago.
Try it (with your teacher, or a grown-up at home). Look at pictures of fossils in a book or on a safe website, with a grown-up. Sort them into body fossils and trace fossils. Do not dig into rocks or take fossils from protected places. Wash your hands afterwards.
Exercise 5A What fossils are
Method. Read the definition.
- Read the definition. A fossil is the remains or trace of a living thing from long ago.fossil
- Write the answer. fossil
Check. Fossils are found in rocks. ✓
Method. Think about what fossils can be.
- Think about examples. Fossils can be animal remains, such as shells and bones, or plant remains, such as leaves.animals and plants
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. Leaves are plant fossils. ✓
Method. Read the definition.
- Read the definition. A trace fossil is a sign that a living thing was there, such as a footprint.sign
- Write the answer. So a footprint is a trace fossil.trace fossil
- Write the answer. trace fossil
Check. Burrows are trace fossils too. ✓
Method. Read the definition.
- Read the definition. A body fossil is a part of the living thing itself.part of the living thing
- Write the words. So the answer is body fossil.body fossil
- Write the answer. body fossil
Check. A body fossil is the animal or plant itself, preserved. ✓
Method. Recall the rock that forms from layers.
- Recall. Fossils form in rock made from layers of sediment, which is sedimentary rock.sedimentary
- Write the answer. sedimentary
Check. Sedimentary rock forms from layers. ✓
Method. Compare the two parts.
- Compare. A shell is hard, and skin is soft and decays quickly.hard
- Choose. So the shell is more likely to be preserved.shell
- Write the answer. shell
Check. Hard parts last longer. ✓
Method. Read the idea.
- Read the idea. Some fossils are of living things that no longer exist.no longer exist
- Write the answer. extinct
Check. Extinct means that the whole group has died out. ✓
Method. Check the definition.
- Read the definition. A fossil is the remains or trace of a living thing from long ago.remains
- Decide. Remains are not alive, so the answer is no.no
- Write the answer. no
Check. A fossil is preserved in rock, not alive. ✓
Method. Apply the definition.
- Apply the definition. A leaf print is a trace of a plant that lived long ago.trace of a plant
- Decide. So the leaf print is a fossil, and the answer is yes.yes
- Write the answer. yes
Check. A print is a trace fossil. ✓
Method. Apply the definition.
- Apply the definition. A footprint preserved in rock is a trace of a living thing.trace
- Decide. So the footprint is a fossil, and the answer is yes.yes
- Write the answer. yes
Check. A trace fossil is still a fossil. ✓
Method. Think about hard parts.
- Think about hard parts. Shells are hard parts that last well.shell
- Write one word. Shell is a good answer; so is a bone or tooth.shell
- Write the answer. shell
Check. Bones and teeth are also hard parts. ✓
Method. Think about what a fossil preserves.
- Think about the fossil. A fossil keeps the shape of a living thing, or its trace, for a very long time.keeps the shape
- Think about the past. So we can learn about living things that lived long ago.long ago
- Write the answer. Accept any sentence that says a fossil is the preserved remains or trace of a living thing, so it shows what lived long ago.
Check. Fossils are evidence of the past. ✓
Method. Think about the types of fossil.
- Think about types. Fossils can be single shells, leaves, footprints, or teeth, not only complete skeletons.not only skeletons
- Decide. So Ruby is not right.no
- Write the answer. no
Check. Many fossils are only parts of a living thing. ✓
Method. Think about decay.
- Think about soft parts. Soft parts decay quickly after death.decay quickly
- Think about preservation. So they are much less likely to be preserved than hard parts.less likely
- Write the answer. Accept any sentence that says soft parts decay quickly, so they are much less likely to be preserved than hard parts.
Check. Hard parts are the ones that last. ✓
How fossils form
Sediment is tiny pieces of rock, sand and mud that settle in layers, usually at the bottom of water. Fossils usually form like this:
- an animal or plant dies in water, and is quickly buried by sediment;
- more and more layers of sediment build up on top, over a very long time;
- the layers are pressed and cemented together to form sedimentary rock;
- minerals from water slowly replace the hard parts, and erosion later exposes the fossil.
The steps are shown in order below.
| Step | What happens |
|---|---|
| 1 | An animal or plant dies in water, and is buried by sediment. |
| 2 | Layers of sediment build up on top, over a very long time. |
| 3 | The layers are pressed and cemented together, and turn into sedimentary rock. |
| 4 | Minerals from water slowly replace the hard parts, and the fossil is exposed by erosion. |
Key ideas
- Fossils usually form when remains are buried quickly in sediment.
- Layers of sediment build up over a very long time, and form sedimentary rock.
- Minerals from water can slowly replace the hard parts of the remains.
- Burial protects the remains from decay and from scavengers.
Method. Read the steps in order.
- Read step 1. Step 1 is the animal or plant dying and being buried.buried
- Write the number. So the first step is number 1.1
- Write the answer. 1
Check. Layers build up after the burial. ✓
Method. Find the step about rock forming.
- Read step 3. The layers are pressed and cemented together to form sedimentary rock.pressed
- Write the word. The process is called compaction and cementation.compaction
- Write the answer. compaction
Check. Pressing squeezes the layers together. ✓
Method. Count the panels.
- Count the panels. The diagram has four panels, labelled 1 to 4.four panels
- Write the number. So there are four steps.4
- Write the answer. 4
Check. Each panel shows one step. ✓
Watch out
Watch out: a fossil does not form in a few days. It takes a very long time for layers to build up and for minerals to replace the remains.
Exam tip
Exam tip. When you describe fossil formation, give the steps in order: buried, layers build up, rock forms, minerals replace the remains.
Try it (with your teacher, or a grown-up at home). Put a layer of sand in a clear jar, then a layer of soil, then a layer of small stones. Tap the jar gently to settle the layers. Notice how the layers are in order. Which layer was added first? Clear up the sand and soil afterwards, and wash your hands.
Exercise 5B How fossils form
Method. Read the definition.
- Read the definition. Sediment is tiny pieces of rock, sand and mud that settle in layers.sediment
- Write the answer. sediment
Check. Sediment often settles at the bottom of water. ✓
Method. Read step 3.
- Read step 3. The layers are pressed and cemented to form sedimentary rock.sedimentary rock
- Write the answer. sedimentary rock
Check. Fossils are usually found in this rock. ✓
Method. Read the steps.
- Read the steps. The first step is the remains being buried quickly.buried
- Write the number. So the first step is step 1.1
- Write the answer. 1
Check. Burial protects the remains. ✓
Method. Read the table.
- Read the last row. The last row is step 4, about minerals and erosion.step 4
- Write the number. So the last step is 4.4
- Write the answer. 4
Check. Erosion exposes the fossil. ✓
Method. Read step 4.
- Read step 4. Minerals from water slowly replace the hard parts.minerals
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. This is how the hard parts become stone. ✓
Method. Read step 1.
- Read step 1. The animal is quickly buried by sediment.buried
- Write one word. The process is burial.burial
- Write the answer. burial
Check. Burial protects remains from decay. ✓
Method. Think about the order of building.
- Think about the order. The layers at the bottom were laid down first.first
- Decide. So the bottom layer is older.bottom
- Write the answer. bottom
Check. The layers are laid down one on top of the other. ✓
Method. Think about how long layers take.
- Think about time. It takes a very long time for layers to build up and for minerals to replace the remains.very long time
- Decide. So Ali is not right.no
- Write the answer. no
Check. Fossil formation takes millions of years. ✓
Method. Think about decay.
- Think about decay. Burial protects the remains from air, decay and scavengers.protects
- Think about minerals. This gives minerals time to slowly replace the hard parts.time
- Write the answer. Accept any sentence that says burial protects the remains from decay and scavengers, which gives time for minerals to replace them.
Check. Burial is the first step of fossil formation. ✓
Method. Follow the formation steps.
- Start with the burial. The animal is buried first, so it is 1.1
- Then the layers. Layers build up next, so it is 2, and the rock forms last, as 3.2, 3
- Write the answer. 1, 2, 3
Check. This matches the four-step diagram. ✓
Method. Think about what happens to remains in the open.
- Think about the remains. On the ground, remains are quickly eaten or decay.eaten or decay
- Think about burial. Burial in sediment is needed to preserve them.preserve
- Write the answer. Accept any sentence that says the remains decay or are eaten before they can be buried and preserved.
Check. Burial is needed for preservation. ✓
Method. Compare hard and soft parts.
- Think about decay. Soft parts decay quickly.decay
- Think about preservation. Hard parts last longer, so minerals can replace them.last longer
- Write the answer. Accept any sentence that says hard parts last much longer than soft parts, so they are more likely to be preserved.
Check. Hard parts are preserved more often. ✓
Method. Think about how fossils form.
- Think about the process. Fossils form when remains are buried in layers of sediment.layers
- Think about the rock. Layers of sediment make sedimentary rock, so fossils are found there.sedimentary
- Write the answer. Accept any sentence that says fossils form when layers of sediment are buried, so they are found in sedimentary rock.
Check. Melted rock does not usually keep the remains. ✓
Fossils show living things long ago
Fossils tell us about living things that inhabited the Earth millions of years ago. In an undisturbed cliff, the lower layers are older, because they were laid down first. The age of each layer tells us how long ago the fossil formed.
The cliff below is made up for these questions. Its ages are invented numbers.
The table gives the fossil and the age of each layer.
| Layer | Fossil | Age (million years) |
|---|---|---|
| A | a shell | 10 |
| B | a leaf | 25 |
| C | a fish | 60 |
| D | a footprint | 120 |
| E | a bone | 200 |
Key ideas
- Lower layers in an undisturbed cliff are older.
- Each fossil tells us about a living thing that lived in that layer's time.
- The age of a fossil is the age of the layer where it is found.
- Compare ages by subtracting the smaller number from the larger number.
Method. Find the largest age.
- Read the ages. The largest age is 200 million years, in layer E.200
- Write the name. So the oldest fossil is the bone.a bone
- Write the answer. a bone
Check. The bottom layer is the oldest in this cliff. ✓
Method. Subtract the younger age from the older age.
- Read the ages. Layer D is 120 million years old, and layer B is 25 million years old.120 and 25
- Subtract. The difference is 120 minus 25.120 - 25 = 95
- Write the answer. 95 million years
Check. 25 + 95 = 120. ✓
Method. Add the five ages, then divide by 5.
- Add. The total of the five ages is 10 + 25 + 60 + 120 + 200.415
- Divide. Divide 415 by 5 layers.415 divided by 5 is 83
- Write the answer. 83 million years
Check. 5 times 83 is 415. ✓
Watch out
Watch out: the age of a fossil is the age of its layer, not of the living thing that you can see. Read the table carefully.
Exam tip
Exam tip. When you compare ages, give the unit, which here is millions of years.
Try it (with your teacher, or a grown-up at home). Make a simple cliff from layers of clay or play dough, one colour for each layer, with a small object pressed into one layer. Write the order of the layers, the oldest at the bottom. Explain which layer the object would be found in, if the top layers were worn away.
Exercise 5C Fossils show living things long ago
Method. Find the shell in the table.
- Read the fossils. The shell is in the top layer, layer A.A
- Write the letter. So the letter is A.A
- Write the answer. A
Check. The shell is the youngest fossil in this cliff. ✓
Method. Find layer C.
- Read the row. Layer C holds a fish.fish
- Write the name. So the fossil is a fish.a fish
- Write the answer. a fish
Check. Layer C is aged 60 million years. ✓
Method. Read the table.
- Read the age. Layer C is 60 million years old.60
- Write the number. So the answer is 60.60
- Write the answer. 60
Check. Layer C is between layers B and D in age. ✓
Method. Find the smallest age.
- Read the ages. The smallest age is 10 million years, in layer A.10
- Write the letter. So the youngest layer is A.A
- Write the answer. A
Check. Layer A is at the top of the cliff. ✓
Method. Read the table.
- Read the row. Layer B holds a leaf.leaf
- Write the name. So the fossil is a leaf.a leaf
- Write the answer. a leaf
Check. A leaf is a plant fossil. ✓
Method. Subtract the youngest from the oldest.
- Read the ages. Layer E is 200 million years and layer A is 10 million years.200 and 10
- Subtract. The difference is 200 minus 10.200 - 10 = 190
- Write the answer. 190
Check. 10 + 190 = 200. ✓
Method. Compare the ages.
- Read the ages. Layer C is 60 million years old, and layer B is 25 million years old.60 and 25
- Decide. Since 60 is more than 25, the fish is older, so the answer is yes.yes
- Write the answer. yes
Check. Layer C is lower down in the cliff than layer B. ✓
Method. Look at the different fossils.
- Look at the fossils. The fossils in the layers are different from each other, for example a shell and a bone.different
- Decide. Different fossils in different layers show that living things changed over time.yes
- Write the answer. yes
Check. The fossils come from different times. ✓
Method. Read the age of layer D.
- Read the table. Layer D is 120 million years old.120
- Write the number. So the footprint was made about 120 million years ago.120
- Write the answer. 120
Check. The layer age is the age of the footprint. ✓
Method. Subtract the younger age from the older age.
- Read the ages. Layer D is 120 and layer B is 25.120 and 25
- Subtract. The difference is 120 minus 25.120 - 25 = 95
- Write the answer. 95
Check. 25 + 95 = 120. ✓
Method. Add the five ages, then divide by 5.
- Add. The total of the five ages is 415 million years.415
- Divide. Divide 415 by 5.415 divided by 5 is 83
- Write the answer. 83
Check. 5 times 83 is 415. ✓
Method. Compare the two ages.
- Read the ages. The shell is in layer A, aged 10 million years, and the bone is aged 200 million years.10 and 200
- Decide. So the shell is younger, and the answer is yes.yes
- Write the answer. yes
Check. The shell is at the top, and the bone is at the bottom. ✓
Method. Think about how layers form.
- Think about the order. Layers build up one on top of another over time.on top
- Think about the bottom. So the layer at the bottom was laid down first, and is the oldest.first
- Write the answer. Accept any sentence that says layers build up over time, so the layers laid down first are at the bottom and are the oldest.
Check. This only holds if the cliff has not been turned over. ✓
Method. Compare the fossils.
- Compare the fossils. A shell and a bone come from different kinds of living thing.different
- Compare the times. They lived 190 million years apart, so they lived at different times.different times
- Write the answer. Accept any sentence that says a shell and a bone come from different living things that lived at very different times.
Check. The ages show the time gap. ✓
Method. Think about a fossil.
- Think about the fossil. A fossil is the preserved remains of a living thing.remains
- Think about the time. The shell is 10 million years old, so it is not alive today.not alive
- Write the answer. Accept any sentence that says the shell is a preserved remain from 10 million years ago, not a living animal today.
Check. The age of the layer tells us when it lived. ✓
Living things change over time
Over millions of years, living things have changed. Some groups have died out, which means that no living members of the group are left. This is called extinction. A group that is extinct is only known from fossils and from records.
Some groups have survived for millions of years. Ferns and dragonflies, for example, have living members today, although they are not the same as the ones that lived long ago.
The table shows four living things, and whether each one is still alive today.
| Living thing | Still alive today? |
|---|---|
| Trilobite | no, extinct |
| Woolly mammoth | no, extinct |
| Fern | yes |
| Dragonfly | yes |
Key ideas
- Extinct means that no living members of a group are left.
- Fossils tell us about groups that are now extinct.
- Some groups have survived, and living things have changed over time.
- Ferns and dragonflies are still alive today.
Method. Find the row that says no.
- Read the table. The trilobite and the woolly mammoth are both extinct.no, extinct
- Write the name. Trilobite is one extinct living thing.Trilobite
- Write the answer. Trilobite
Check. The woolly mammoth is also extinct. ✓
Method. Count the rows that say extinct.
- Count the rows. The trilobite and the woolly mammoth are extinct.two rows
- Write the number. So two of the four living things are extinct.2
- Write the answer. 2
Check. The fern and the dragonfly are still alive. ✓
Method. Read the dragonfly row.
- Read the row. The table says yes for the dragonfly.yes
- Decide. So the dragonfly is alive today.yes
- Write the answer. yes
Check. Dragonflies have living members today. ✓
Watch out
Watch out: an extinct group is not the same as a group that has changed. A fern alive today is not the same as a fern from millions of years ago, but ferns have not died out.
Exam tip
Exam tip. Say that a group is extinct when none of its members are alive, and use the fossil record as evidence.
Try it (with your teacher, or a grown-up at home). Look at a picture of a fern and a picture of a fossil fern, if you can find one in a book or safe website, with a grown-up. Compare the leaves. Talk about what has stayed the same, and what might have changed.
Exercise 5D Living things change over time
Method. Read the definition.
- Read the definition. Extinction means that no living members of a group are left.extinction
- Write the answer. extinction
Check. Extinct groups are known from fossils. ✓
Method. Read the rows.
- Read the rows. The table says the trilobite is extinct, and the fern is alive.trilobite extinct
- Write the name. So the extinct one is the trilobite.Trilobite
- Write the answer. Trilobite
Check. The fern is still alive today. ✓
Method. Read the table.
- Read the row. The table says no, extinct, for the woolly mammoth.no
- Decide. So the answer is no.no
- Write the answer. no
Check. Mammoths are known from fossils and remains. ✓
Method. Count the rows that say yes.
- Read the rows. The fern and the dragonfly say yes.fern and dragonfly
- Write the number. So two are still alive.2
- Write the answer. 2
Check. Two are extinct, and two are alive. ✓
Method. Read the table.
- Read the row. The fern row says yes.yes
- Decide. So ferns are still alive.yes
- Write the answer. yes
Check. Ferns have living members today. ✓
Method. Think about change over time.
- Think about change. Living things change over millions of years, and this change is called evolution.change over time
- Write one word. So the word is evolution.evolution
- Write the answer. evolution
Check. Evolution is covered in more detail in Chapter 6. ✓
Method. Use the table.
- Read the table. The trilobite and the woolly mammoth are extinct.extinct
- Decide. So Ali is not right.no
- Write the answer. no
Check. Some groups have died out. ✓
Method. Count both kinds of row.
- Count the extinct rows. Two rows say extinct.2
- Count the living rows. Two rows say yes.2 and 2
- Write the answer. 2 and 2
Check. The table has four rows. ✓
Method. Think about survival.
- Think about the groups. Some groups have survived for millions of years.survived
- Think about change. They have changed over time, so their living members are still here.changed
- Write the answer. Accept any sentence that says these groups have survived and changed over time, so living members are still alive.
Check. Survival and change are both part of the story. ✓
Method. Think about fossils.
- Think about the living. Extinct groups have no living members to study.no living members
- Think about the fossils. Fossils show what they looked like, so we know about them.looked like
- Write the answer. Accept any sentence that says fossils are the only evidence of groups that are no longer alive, so they show what they looked like.
Check. Fossils are the record of the past. ✓
Method. Think about the layers.
- Think about different layers. Different fossils are found in layers of different ages.different layers
- Think about change. So the living things in the layers have changed over time.changed
- Write the answer. Accept any sentence that says different fossils are found in different layers, so the living things changed over time.
Check. Layers in time order show change. ✓
Using fossils as evidence
Evidence is information from observations or tests that can support an idea, or refute it, which means show that it is wrong. Fossils are evidence about the living things of the past.
Fossils have limits. Soft parts are rarely preserved, and the fossil record has gaps. So a fossil can support an idea, but it does not always show everything. A new fossil can change what we think, if it is found in the right layer.
Key ideas
- Evidence from fossils can support or refute an idea about the past.
- Two fossils can be compared by their ages, to decide whether they lived at the same time.
- Fossils rarely show soft parts, so they cannot show everything.
- The fossil record has gaps, so some living things are not known from fossils.
Method. Compare the two ages.
- Read the ages. The bone is 200 million years old, and the footprint is 120 million years old.200 and 120
- Decide. The ages are different, so they lived at different times.different times
- Write the answer. no
Check. The difference is 80 million years. ✓
Method. Check the evidence.
- Read the evidence. The bone and footprint are in different layers, with different ages.different layers
- Decide. So the evidence does not support Sam's idea.does not support
- Write the answer. does not support
Check. Being in the same cliff does not mean being the same age. ✓
Method. Think about what is rarely preserved.
- Think about soft parts. Soft parts, such as skin and muscle, decay quickly and are rarely preserved.soft parts
- Write one word. So fossils rarely show soft parts.soft parts
- Write the answer. soft parts
Check. Fossils mostly show hard parts. ✓
Watch out
Watch out: a fossil can support an idea, but one fossil does not prove a whole idea. Look at the evidence, and check whether it is in the right layer.
Exam tip
Exam tip. When you use fossil evidence, say what the fossil shows and whether it supports or refutes the idea.
Try it (with your teacher, or a grown-up at home). Look at three pictures of fossils with a grown-up, and write one idea that each could support. For each, write one thing it could not show. Discuss your answers with a partner.
Exercise 5E Using fossils as evidence
Method. Read the definition.
- Read the definition. Evidence is information from observations or tests that supports or refutes an idea.evidence
- Write the answer. evidence
Check. Fossils are one type of evidence about the past. ✓
Method. Read the limit of fossils.
- Read the limit. Soft parts decay quickly, so they are rarely preserved.decay
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. Hard parts are more often preserved. ✓
Method. Read the limit of fossils.
- Read the limit. Not every living thing has been preserved, so the record has gaps.gaps
- Decide. So the answer is yes.yes
- Write the answer. yes
Check. Gaps mean we cannot know everything from fossils alone. ✓
Method. Compare the ages.
- Read the ages. The bone is 200 and the footprint is 120 million years old.200 and 120
- Decide. They are different ages, so the answer is no.no
- Write the answer. no
Check. The difference is 80 million years. ✓
Method. Think about layers.
- Think about layers. Fossils in different layers have different ages.different layers
- Decide. So being in the same cliff does not show they are the same age.no
- Write the answer. no
Check. Each layer has its own age. ✓
Method. Compare hard and soft parts.
- Compare. Bones are hard and last longer than skin.bones last
- Choose. So bones are more likely to be found as fossils.bones
- Write the answer. bones
Check. Hard parts are more likely to be preserved. ✓
Method. Think about the order of layers.
- Think about the order. In an undisturbed cliff, the top layer is the youngest, so it should not be older than the layer below.youngest at the top
- Decide. A 300 million year old fossil at the top does not fit, so the answer is does not fit.does not fit
- Write the answer. does not fit
Check. The ages do not follow the order of the layers. ✓
Method. Compare the ages.
- Read the ages. The fish is 60 million years old and the leaf is 25 million years old.60 and 25
- Decide. They lived 35 million years apart, so the evidence does not support Ali.does not support
- Write the answer. does not support
Check. The difference is 35 million years. ✓
Method. Think about what is not preserved.
- Think about soft parts. Colour and sound are not preserved in a fossil, and soft parts usually decay.not preserved
- Write one thing. Any one of these cannot be seen in a fossil.one thing
- Write the answer. Accept any one of: the colour, the sounds it made, the soft parts, how it behaved.
Check. A fossil shows the hard parts that lasted. ✓
Method. Think about evidence.
- Think about one piece. One fossil is only one piece of evidence.one piece
- Think about more. More evidence from more fossils and tests is needed to be sure.more evidence
- Write the answer. Accept any sentence that says one fossil is only one piece of evidence, and more evidence is needed to be sure.
Check. Scientists look for patterns across many results. ✓
Method. Think about what refutes an idea.
- Think about the fossil. A fossil with an age that does not fit the idea can show it is wrong.does not fit
- Think about the layers. A fossil in the wrong layer, or a wrong age, can refute an idea.wrong age
- Write the answer. Accept any sentence that says a fossil found in the wrong layer or with the wrong age can show that an idea is wrong.
Check. Refuting an idea means showing it is wrong. ✓
Method. Think about how ages are found.
- Think about the ages. The age of a fossil comes from the layer it is in, which is an estimate.estimate
- Think about certainty. So an exact date would be uncertain, and it needs care.uncertain
- Write the answer. Accept any sentence that says ages come from the layers, which are estimates, so the exact date is uncertain.
Check. Scientists say how sure they are. ✓
Chapter summary
| Skill | Method |
|---|---|
| What fossils are | The remains or trace of a living thing that lived long ago. Body fossils are parts; trace fossils are signs. |
| How they form | Remains are buried in sediment. Layers build up, rock forms, and minerals replace the hard parts. |
| Dating layers | In an undisturbed cliff the lower layers are older. Compare fossil ages by subtraction. |
| Change over time | Living things have changed over millions of years. Some groups are extinct, and others are still alive. |
| Evidence | Fossils can support or refute ideas. They rarely show soft parts, and the record has gaps. |
Can you…?
- I can say what a fossil is, and give a body fossil and a trace fossil
- I can describe how a fossil forms, in order
- I can use the order of layers and the ages of fossils to say which is older
- I can explain that some groups are extinct, and living things have changed
- I can say whether fossil evidence supports or refutes an idea, and what fossils cannot show
Key terms
- fossil
- the remains or trace of a living thing that lived long ago, preserved in rock
- body fossil
- a part of a living thing, such as a bone or a shell, that has been preserved
- trace fossil
- a sign that a living thing was there, such as a footprint
- sediment
- tiny pieces of rock, sand and mud that settle in layers
- sedimentary rock
- rock formed when layers of sediment are pressed and cemented together
- extinct
- no living members of a group are left
- extinction
- when a group of living things has died out completely
- evolution
- the way that living things change over many generations and millions of years
- evidence
- information from observations or tests that can support or refute an idea
- erosion
- the wearing away of rock by wind, water or ice, which can expose fossils
Exercise 5Z Check-up
Method. Recall the definition.
- Recall. A fossil is the remains or trace of a living thing from long ago.fossil
- Write the answer. fossil
Check. Fossils are preserved in rock. ✓
Method. Read the definitions.
- Read the definitions. A trace fossil is a sign of a living thing, such as a footprint.sign
- Write the answer. trace fossil
Check. A body fossil is part of the living thing. ✓
Method. Recall the rock.
- Recall. Fossils form in layers of sediment, so they are found in sedimentary rock.sedimentary
- Write the answer. sedimentary
Check. Layers of sediment make this rock. ✓
Method. Read the steps.
- Read step 1. The first step is that an animal or plant is buried by sediment.buried
- Write the answer. an animal is buried
Check. Burial comes before the layers build up. ✓
Method. Think about how layers are laid down.
- Think about the order. The lower layers were laid down first, so they are older.first
- Write the answer. lower
Check. The top layer is the youngest. ✓
Method. Read the table.
- Read the row. Layer E holds a bone, aged 200 million years.200
- Write the answer. 200
Check. The bone is the oldest fossil in the cliff. ✓
Method. Subtract the younger age from the older age.
- Read the ages. Layer C is 60 and layer A is 10.60 and 10
- Subtract. The difference is 60 minus 10.60 - 10 = 50
- Write the answer. 50
Check. 10 + 50 = 60. ✓
Method. Read the table.
- Read the rows. The trilobite is extinct, and the dragonfly is still alive.dragonfly alive
- Write the answer. Dragonfly
Check. The trilobite is extinct. ✓
Method. Think about decay.
- Think about soft parts. Soft parts decay quickly after death.decay quickly
- Think about the result. So they are rarely preserved as fossils.rarely
- Write the answer. Accept any sentence that says soft parts decay quickly, so they are less likely to be preserved than hard parts.
Check. Hard parts last longer. ✓
Method. Compare the ages.
- Read the ages. The bone is 200 million years old and the footprint is 120 million years old.200 and 120
- Decide. Their ages are different, so they were made at different times.different times
- Write the answer. Accept any sentence that says their ages are very different, 200 and 120 million years, so they were made at different times.
Check. Ages in the table give the evidence. ✓
Total 15 marks. Allow about 15 minutes.
Exercise 5X Practice test questions
Method. Recall the rock.
- Recall. Layers of sediment form sedimentary rock.sedimentary
- Write the answer. sedimentary
Check. Fossils are often found in this rock. ✓
Method. Find the largest age.
- Read the ages. The largest age is 200 million years, in layer E.200
- Write the letter. So the oldest layer is E.E
- Write the answer. E
Check. Layer E is the bottom layer. ✓
Method. Add the five ages, then divide by 5.
- Add. The total is 10 + 25 + 60 + 120 + 200 = 415.415
- Divide. Divide 415 by 5.415 divided by 5 is 83
- Write the answer. 83 million years
Check. 5 times 83 is 415. ✓
Method. Think about the type of fossil.
- Name the type. A part of a living thing, such as a shell, is a body fossil.body fossil
- Give the reason. The shell is part of the animal, not a sign that it was there.part of
- Write the answer. Accept any sentence that says it is a body fossil, because it is a part of the living thing itself.
Check. A footprint would be a trace fossil instead. ✓
Method. Follow the formation steps.
- Find the first event. The animal is buried first, before the layers build up and the rock forms.buried first
- Write the number. The event that happens first is event 2.2
- Write the answer. 2
Check. Burial, then layers, then rock, then minerals. ✓
Method. Compare soft and hard parts.
- Think about the soft animal. Soft parts decay quickly.decay
- Think about the shell. Hard parts last longer, so they are more often preserved.last longer
- Write the answer. Accept any sentence that says soft parts decay quickly, while hard parts such as shells last longer and are more likely to be preserved.
Check. Hard parts are preserved more often. ✓
Method. Read the table.
- Read the rows. The table says the woolly mammoth is extinct, and the fern is alive.extinct
- Write the name. So the extinct group is the woolly mammoth.Woolly mammoth
- Write the answer. Woolly mammoth
Check. Ferns are still alive. ✓
Method. Think about the layers.
- Think about the fossils. Different fossils are found in layers of different ages.different ages
- Think about change. So the living things in the older layers were different.different
- Write the answer. Accept any sentence that says different fossils are found in layers of different ages, so the living things have changed over time.
Check. Layers in time order show change. ✓
Method. Think about layers.
- Think about the layers. Each layer has its own age.own age
- Think about the claim. So fossils in different layers did not live at the same time.not the same time
- Write the answer. Accept any sentence that says layers have different ages, so fossils in different layers did not live at the same time.
Check. Evidence has to fit the layers. ✓
Method. Think about what is not preserved.
- Think about the colour. The colour of an animal is usually not preserved in a fossil.colour
- Write the answer. colour
Check. Any soft part, such as skin, is also not usually preserved. ✓