Year 3 science · Key Stage 2 · Rocks
Year 3 rocks, fossils and soils: grouping rocks and how fossils form
In Year 3, children learn that there are many kinds of rock and that they can be compared and grouped by what they look like and how they behave. They find out in simple terms how fossils form when living things are trapped in rock, and they learn that soil is made from rocks mixed with organic matter. The work often involves a hand lens, a few rock samples and a walk outside.
Rocks, fossils and soils, explained
Children begin by looking closely at rocks and describing them using their senses and simple tests. Is it hard or soft? Rough or smooth? Does it have a pattern of layers, or tiny sparkling crystals, or separate grains you can feel? What colour is it? Is it heavy for its size? Does it soak up water? A hand lens or a simple microscope is used to see the crystals or grains. Pupils then group rocks according to what they have found, so the grouping rules come from the rocks rather than from a list. Many schools also introduce the names of three kinds of rock: igneous, which formed from molten rock that cooled (granite and basalt are examples); sedimentary, made from layers of sediment squashed together over a long time (sandstone, limestone and chalk); and metamorphic, which are rocks changed by heat and pressure (marble and slate). Those names are a common choice rather than something every school has to teach.
Rocks are used in the places children know, such as stone walls and buildings, paving, roofs and gravestones. Looking at them shows why people choose particular rocks. Slate splits into thin flat sheets and doesn’t let water through, so it is used for roofs. Granite is very hard and wears slowly, so it is used for kerbstones and gravestones. Softer rocks like some sandstones and limestones can weather and wear away more quickly, and children can spot where the surface of a stone has crumbled over many years.
Fossils are the next topic. Children learn in simple terms that a fossil is the preserved remains or traces of a living thing that died long ago and became trapped in rock. Typically, a plant or animal such as a shellfish dies and sinks into mud or sand on a sea bed. Soft parts rot away, but hard parts like shells and bones stay. More layers cover it and, over millions of years, the sediment is squashed and hardened into rock with the shape of the shell or bone preserved inside. Later the rock may be lifted up and worn away, and the fossil can be found. Fossils are mostly found in sedimentary rock. Dinosaurs make good stories, but a fossil can be a seashell, a leaf or a footprint, and most are much smaller creatures.
Finally, children learn that soil is made from rocks and organic matter. Over a very long time, wind, rain, ice and plant roots break rock into tiny pieces. These mix with organic matter, the remains of dead plants and animals that rot away, along with air, water and living things like worms. Soils differ in colour, texture and how much water they hold, and children compare samples from different places, perhaps with a link to geography.
Words your child will hear
- Property
- A way of describing a rock, such as hard, rough, layered or absorbent.
- Grains and crystals
- The tiny pieces that make up a rock. Grains are separate rounded pieces stuck together; crystals fit tightly together like a jigsaw and often glint in the light.
- Permeable
- Lets water soak into it. Chalk is permeable; granite mostly isn’t.
- Sedimentary
- A kind of rock made from layers of tiny pieces (sediment) pressed together, such as sandstone.
- Fossil
- The remains or traces of a living thing that died long ago, preserved in rock.
- Organic matter
- Material that comes from living things, such as rotted leaves and the remains of animals.
- Soil
- A mixture of tiny pieces of rock, organic matter, water and air that plants grow in.
What the National Curriculum says
In Year 3, pupils should be taught to:
- Compare and group together different kinds of rocks on the basis of their appearance and simple physical properties
- Describe in simple terms how fossils are formed when things that have lived are trapped within rock
- Recognise that soils are made from rocks and organic matter
Objectives from the National Curriculum in England, © Crown copyright, used under the Open Government Licence v3.0.
Try it: comparing three rocks
You have three rock samples: granite, chalk and slate. How could you compare and group them?
- Look closely with a hand lens and describe each one. Granite has a speckled pattern of crystals that sparkle. Chalk is white and powdery looking, with no visible crystals. Slate is dark grey, smooth and looks as if it is made of thin sheets.
- Test how hard each one is. Scratch each one gently with a fingernail. The chalk is scratched easily and white powder comes off, so it is soft. The granite and slate are not scratched, so they are harder.
- Test whether water soaks in. Use a dropper to put one drop of water on each rock. The drop sinks into the chalk and stays on top of the granite and slate.
- Test whether any pieces rub off by rubbing two similar rocks together over a sheet of paper. The chalk leaves a lot of white dust; the granite leaves almost none.
- Choose a grouping rule from your results, such as “soft and soaks up water” and “hard and does not soak up water”, and say which rocks fit in each group.
Group 1, soft and soaks up water: chalk. Group 2, hard and does not soak up water: granite and slate. Granite can be told apart from slate because it is made of sparkly crystals while slate is smooth and splits into thin layers.
Common mistakes and how to help
Thinking all rocks are hard and look alike
Children picture a grey stone from the garden, so the idea of a soft rock like chalk, or a layered one, is surprising.
What helps: Collect different rocks and describe each in detail. Rub them, drop water on them and look at them through a magnifier so differences can be spotted.
Believing a fossil is the actual animal or that fossils are only dinosaurs
Dinosaur skeletons in museums and films make fossils seem like preserved bodies of big animals.
What helps: A fossil is usually a copy in stone, or a trace such as a footprint. Look at examples such as shells, ammonites and leaves, and talk about how they got buried.
Thinking soil is just crushed rock or just “dirt”
Soil looks like a uniform brown material, so children don’t notice what is in it.
What helps: Look at a handful with a magnifier. You will see tiny stones, bits of dead leaf and roots, and perhaps minibeasts. Soil is rock pieces plus organic matter, with air and water.
Grouping rocks only by colour
Colour is the first thing children notice, but rocks of the same kind can vary in colour and different rocks can look alike.
What helps: Ask for a second and a third property: How does it feel? Does it have grains or crystals? Does it absorb water? Colour is one clue, not the whole story.
How to help at home
- A rock walk. Look at stone walls, buildings, paving and gravestones in your area. Notice colour, texture and where the surface has worn away. Ask why that stone may have been chosen. Don’t climb on walls or collect from places where it’s not allowed.
- Start a collection. Collect a few pebbles and stones from the garden or a walk, and sort them using a rule your child chooses. Then swap and ask someone else to work out the rule.
- Shake a soil jar. Put a few spoonfuls of garden soil in a clear plastic bottle, add water and shake. Leave it for a day and look at the layers as the heavier pieces settle first. Wash your hands after handling soil.
- Make a fossil imprint. Press a shell, a leaf or a toy into a flat piece of modelling clay or play dough, then lift it away. The shape left behind shows how a fossil can record a living thing. Talk about the many layers and the great length of time needed to make a real one.
Related topics
Updated .