1. Weathering A process that breaks down rocks into smaller fragments.
Mechanical (physical) Weathering
Chemical Weathering

2. Mechanical Weathering
Breaks apart rocks without changing their chemical composition.
Plants
Ice

3. Plants
Roots of plants grow into the cracks of rocks. As the root grows it wedges the rock apart.

5. Ice Wedging
Water enters a crack in a rock. As the water freezes it expands the crack. When it thaws it goes deeper into the expanded crack. As this process repeats itself the rock eventually breaks.

7. Chemical Weathering
Occurs when water, air, or other substances react with the minerals in rocks.
Water: hydrogen and oxygen in water react with the chemicals in some rocks and new compounds form.
Acids: Carbonic acid dissolves some minerals.

8. Rust stain

9. Chemical Weathering
Acids in Plants: Some plants naturally produce acids which can also dissolve minerals.
Oxygen: reacts with some minerals causing oxidation.

10. OXIDATION

11. Weathering forms Soil
Soil: is a mixture of weathered rock, organic matter, mineral fragments, water, and air.

12. Soil Profile Soil is divided into three sections called horizons.
Horizon A: Contains Humus (organic matter turning the soil dark). Humus provides nutrients for plants, providing nitrogen, phosphorus, potassium, and sulfur. Humus also helps soil retain water.

13. Soil Profile
Horizon B: contains minerals leached from horizon A. Leaching is a process by which materials are removed from soil as they are dissolved in water.

14. Soil Profile
Horizon C: contains some materials that were leached from horizon B. Horizon C also contains partly weathered rock that is beginning the long, slow process of evolving into soil.