Lesson focus: How can loose sand become rock?
Sequence weatheringWhen rock is broken down where it is, by weather, chemicals or living things., erosionWhen bits of rock are worn away and carried off by water, wind or ice., depositionWhen moving water, wind or ice drops the bits of rock it was carrying., compactionWhen layers of sediment are squashed together by the weight of layers above. and cementationWhen minerals glue grains of sediment together to make rock..
Build on earlier learning
MixturesConsider the properties of different particles in a mixture.
Practical
Modelling sedimentary rock
- Shake sand, gravel and soil in a jar of water and let it settle.
- Observe the layers: larger, denser grains settle first.
- Relate the layers to compaction and cementation over time.
Record: A labelled drawing of the layers with grain sizes.
You will be successful when you can…
- Distinguish weathering from erosion.
- Sequence a clastic pathway.
- Explain compaction and cementation.
- Recognise other sedimentary routes.
Words that carry the science
- weathering
- Breakdown of rock in place.
- erosion
- Removal and transport of weathered material.
- deposition
- Settling of transported sediment.
- compaction
- Grains pressed closer together during burial.
- cementation
- Minerals deposited between grains bind them together.
Keep weathering, transport and rock formation as distinct processes
01Break down before moving
Physical, chemical or biological weatheringWhen rock is broken down where it is, by weather, chemicals or living things. acts on rock in place. erosionWhen bits of rock are worn away and carried off by water, wind or ice. then removes and transports material by water, wind, ice or gravity.
02Flow controls deposition
When a transporting fluid loses energy, larger or denser particles often settle sooner, while fine particles may remain suspended longer.
03Burial turns sediment into rock
Overlying layers compact sediment and minerals precipitated in pore spaces cement grains. This describes clastic rocks; chemical precipitation and biological material form others.
Sedimentary rock forming
Rivers carry broken bits of rock into lakes and seas. The bits settle in layers: big, heavy grains sink fastest, fine clay last. Layers build up; their weight compacts the lower layers and minerals cement them into rock.
Brown: sand and pebbles (sink fastest). Tan: silt. Grey: clay (sinks slowest).
Controls
Speeds are illustrative; real layers take thousands to millions of years. Fossils are found in sedimentary rocks such as sandstone, limestone and mudstone.
Explain graded sediment
A flood layer has coarse grains at the bottom and finer grains above.
- Fast water can carry a wide range of grain sizes.
- As flow loses energy, larger grains settle first.
- Finer particles stay suspended longer.
- Continued slowing deposits finer grains above the coarse layer.
How to make the reasoning visible: The vertical grain-size pattern can preserve evidence of changing flow energy.
Process and evidence sequence
Connect each process to an observable consequence.
| Process | Location/action | Evidence | Common confusion |
|---|---|---|---|
| Weathering | Rock breaks in place | Cracks/fragments | Not transport |
| Erosion | Material removed/moved | Rounded grains/pathway | Not deposition |
| Deposition | Sediment settles | Layers/graded beds | Not cementation |
| Compaction | Burial pressure | Reduced pore space | Does not melt |
| Cementation | Minerals bind grains | Cement between grains | Not simple drying |
How can several layers record several events?
Why may coarse grains lie below fine grains?
Use the table. What is the difference between weathering and erosion?
Check your understanding
Answer from memory, then check against the suggested answer.
What is weathering?
What is erosion?
What is deposition?
What is compaction?
Give an example of a sedimentary rock.
Describe how loose sand becomes sandstone.
Why is chalk a warning against treating the clastic sequence as universal?
Why are fossils usually found in sedimentary rocks and not igneous rocks?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
Describe how loose sediment becomes sedimentary rock.
(4)Total for this question: 4 marks
Command word: Give the stages in causal order and do not include melting.