Pick one before you read on. It is fine to be wrong.
By the end you can
Draw the rock cycle with melting, cooling, burying and lifting
Explain how one rock can become another over millions of years
Does a rock stay the same for ever? It seems so, because we cannot see it change. But over millions of years, rocks change from one kind into another. The path they follow is the rock cycle.
Start deep underground. There, rock can get so hot that it melts. Melted rock under the ground is magma. Magma that reaches the surface is called lava.
Draw it first
Draw the rock cycle
1 Draw a box for magma and a box for igneous rock. Draw an arrow from magma to igneous rock and write cools on it.
2 Add a box for sediment. The arrow into it says lifted and worn away.
3 Add a box for sedimentary rock. The arrow into it says buried and pressed.
4 Add a box for metamorphic rock. Heat and pressure make it. Draw an arrow from it back to magma and write melts.
When magma cools, it hardens into igneous rock. Magma that cools slowly under the ground makes big crystals, like granite. Lava that cools fast on the surface makes small crystals, like basalt.
Slow cooling gives big crystals. Fast cooling gives small ones.
Rock deep down can be lifted up when plates push together. At the surface, weathering and erosion wear it into sediment.
Plates that push together can lift rock up. Then weathering and erosion wear the top away.
Rivers drop sediment in layers on a lake floor or the sea floor. New layers bury the old ones. The weight presses the lower layers, and minerals in the water glue the bits together. The layers become sedimentary rock.
The lower layers are buried and pressed. They have become rock.
Rock buried deeper still gets hot and is squeezed hard. Heat and pressure can change it without melting it. Shale becomes slate. Limestone becomes marble. These are metamorphic rocks.
If the rock gets hotter, it melts into magma. Then the cycle can start again. One turn of the cycle takes millions of years.
The ring is not the only way round. A rock can take a shortcut. Igneous rock can be buried and heated into metamorphic rock, without becoming sediment first. Metamorphic rock can be lifted and worn away to sediment.
Solid arrows are the ring. Dashed arrows are shortcuts.
See it three ways
As a picture
In words
Each row changes one rock into the next, and each row ends where the next begins. Lifting brings deep rock up, so that it can be worn away. Cooling, wearing, pressing, heating and melting are the changes.
Try it
Make a block of sedimentary rock
You need: sand, a spoon of mud or clay soil, water, a small cup, a sunny place.
Be safe: Wash your hands after you touch mud. Never look at the Sun.
Mix a cup of sand with a spoon of mud. Add a little water and stir to a thick paste.
Press the paste firmly into the cup. Leave it in the sun for two days.
Tip the block out. Press on it gently with your thumb.
What you will see: The mud has glued the sand into a block, as minerals glue sand into sandstone. Your block crumbles more easily than real rock, because real rock was pressed for millions of years.
If you cannot try it, this is what happens.
A wrong idea many people have
Rocks must follow the cycle in one fixed order.
Why it feels right: A picture of a ring with arrows seems to show only one path.
The test that breaks it: A sedimentary rock can be lifted and worn away again without being heated. An igneous rock can be buried and changed into a metamorphic rock. Any rock can be melted.
What is true: There are many shortcuts. Any kind of rock can become any other kind, given enough time.
Key words
rock cycle
the slow change of rock from one kind to another and back.
magma
melted rock under the ground.
lava
melted rock that has reached the surface.
Back to your guess
The answer is C: Yes. Over millions of years, heat, pressure, weathering and melting can turn it into another kind.
Rocks do change kind, but very slowly. One full turn of the rock cycle takes millions of years.
Check yourself
Try each one before you look. A wrong answer tells you where to go next.
What happens when magma cools and hardens?
See the answer
It becomes igneous rock.
Igneous rock forms when melted rock cools and hardens.
If you chose A: Sedimentary rock is made from pressed layers of sediment. Cooled magma makes igneous rock. Go to S3.11.4.
If you chose C: Metamorphic rock is changed by heat and pressure without melting. Magma that cools makes igneous rock. Go to S3.11.4.
Which step turns solid rock into sediment?
See the answer
Weathering and erosion
Weathering breaks rock into small pieces. Erosion carries them away. The pieces are sediment.
If you chose B: Cooling turns magma into rock. It does not wear rock into pieces. Go to S3.11.4.
If you chose C: Burying comes after sediment exists. It presses sediment into rock. Go to S3.11.4.
How is sedimentary rock made?
See the answer
Layers of sediment are buried, pressed and glued together.
The weight of new layers presses the old ones. Minerals glue the bits into rock.
If you chose A: That makes igneous rock. Sedimentary rock never melts on the way. Go to S3.11.4.
If you chose C: That makes metamorphic rock. Sedimentary rock is built from pressed layers of sediment. Go to S3.11.4.
Rock that formed deep underground is found in the hills. What brought it up?
See the answer
Plates pushing together lifted it, and the rock above wore away.
Moving plates can lift rock up. Weathering and erosion then wear away the rock above, and the deep rock shows.
If you chose A: Rivers only carry rock downhill. Lifting rock needs the huge push of moving plates. Go to S3.11.4.
If you chose B: Wind cannot lift solid rock from deep down. Plates push it up over millions of years. Go to S3.11.4.
About how long does it take for a rock to change from one kind into another?
See the answer
Millions of years
The rock cycle is very slow. One turn takes millions of years.
If you chose B: We would see rock change in front of us. It is far too slow for that. Go to S3.11.4.
If you chose C: One year is too short. Burying, pressing and heating rock take millions of years. Go to S3.11.4.
Can sedimentary rock melt and become igneous rock?
See the answer
Yes. Buried deep and heated, it melts into magma. The magma can cool into igneous rock.
Any kind of rock can melt. When the magma cools, it becomes igneous rock.
If you chose A: That is only one path. If the rock gets hot enough, it melts, whatever kind it was. Go to S3.11.4.
If you chose C: Every kind of rock can melt if it gets hot enough. Go to S3.11.4.
From an earlier chapter
What is erosion?
See the answer
The carrying away of rock pieces by a river, wind or waves
Erosion carries away the pieces that weathering breaks off.
If you chose B: That is weathering. Erosion is the carrying away of the pieces. Go to S3.11.3.
If you chose C: Melting makes magma. Erosion happens at the surface and carries pieces away. Go to S3.11.3.
Keep it
Copy this into your exercise book.
Magma cools to igneous rock. Rock wears into sediment. Sediment is buried and pressed into sedimentary rock. Heat and pressure make metamorphic rock. More heat melts it.
Draw: Draw five boxes in a ring: magma, igneous, sediment, sedimentary, metamorphic. Add an arrow with a word between each pair. Add one dashed shortcut.
