1. Sedimentary rocks
Thursday, 15 November 2018
Learning objectives;
To be able to describe how sedimentary rocks form and how dinosaur fossils may appear in them.

2. Sedimentary rocks
Weathering breaks up rocks into smaller pieces, or sediments. There are 3 types of weathering…

3. Sedimentary rocks
Chemical weathering…
…happens when acids in rainwater react with some rock minerals. Chemical weathering makes gravestone writing go blurry.

4. Chemical Weathering
Chemical weathering

5. Sedimentary rocks
Biological weathering…
… happens when plant roots or animal actions break up rocks.

6. Biological weathering

7. Sedimentary rocks
Physical weathering…
for example freeze-thaw weathering, happens when water gets into rock cracks:
On cold nights, water freezes.
When water freezes, it expands.
The ice pushes against the sides of the crack. The crack gets bigger.
This happens again and again. The rock breaks.

8. Freeze-thaw weathering

9. Sedimentary rocks
Erosion
Sediments are transported away by water, wind, gravity or ice. This is erosion.

10. Erosion
Erosion

11. Sedimentary rocks
When rivers reach the sea, they slow down. The tiny sediments suspended in the water drop to the bottom and settle in a layer. This is deposition, or sedimentation.
New layers settle on top of older layers.
Eventually the sediments in the layers stick together. This is cementation.
The layers become hard. They are now strata.

12. Sedimentary Rocks
Sedimentary Rocks

13. 8.3 Fossil formation Fossil formation - 1 An animal or plant dies.
It falls onto mud or sand.

14. 8.3 Fossil formation Fossil formation - 2
More mud or sand buries the body.

15. 8.3 Fossil formation Fossil formation - 3
Soft parts of the body rot away.
Bones and teeth remain.

16. 8.3 Fossil formation Fossil formation - 4
The mud or sand becomes rock.
Hard minerals may replace the hard parts of the body.

17. 8.3 Fossil formation Fossil formation - 5
Later, rocks around the fossil wear away. The fossil is exposed.

18. Fossils
Fossils

19. Show a video clip about the discovery of the fossilised remains of a three-year-old girl – ‘Selam’ – in Ethiopia.