Weathering and Soil Formation

1. Weathering and Soil Formation

2. The Effects of Weathering • Weathering is the process that breaks down rock and other substances at Earth's surface. • What contributes to weathering? • Heat • Cold • Water • Ice • all contribute to weathering.

3. The Effects of Weathering • Forces of weathering break rock into smaller and smaller pieces. • Forces of erosion carry the pieces away. • Erosion is the movement of rock particles by wind, water, ice, or gravity • There are two kinds of weathering: • Mechanical weathering • Chemical weathering

4. Mechanical Weathering • Weathering in which rock is physically broken into smaller pieces is called mechanical weathering. • smaller pieces have same composition as the original rock • Mechanical weathering breaks rock by • Freezing and thawing • Release of pressure • Growth of plants • Actions of animals • Abrasion • Abrasion refers to the grinding away of rock, by rock particles carried by water, ice, wind, or gravity.

5. Mechanical Weathering

6. Chemical Weathering • Chemical weathering is the process that breaks down rock through chemical changes. • The agents of chemical weathering include • Water • Oxygen • Carbon dioxide • Living organisms • Acid rain • Chemical weathering produces rock particles that have a different mineral makeup from the rock they came from.

7. Chemical Weathering

8. Chemical and Mechanical Weathering • Chemical and mechanical weathering often work together. • As mechanical weathering breaks rock into pieces, more surface area becomes exposed to chemical weathering.

9. Water • How does water contribute to weathering? • Water is the most important agent of chemical weathering. • Water weathers rock by dissolving it. • When a rock or other substance dissolves in water, it mixes throughout the water to make a solution. • Over time, many rocks will dissolve in water. • Water can also freeze, expand in rock and break it apart. (Ice wedging)

10. Oxygen • How does oxygen contribute to weathering? • The oxygen gas in air is an important cause of chemical weathering. • Bicycle or metal tool outside in the rain • Iron combines with oxygen in the presence of water in a process called oxidation. • The product of oxidation is rust. • Rust makes rock soft and crumbly

11. Living Organisms   • How do living organisms contribute to weathering? • Weak acids that slowly dissolve rock around the roots. • Plantlike organisms that grow on rocks—also produce weak acids that chemically weather rock.

12. Acid Rain   • How does acid rain contribute to weathering? • Over the past 150 years, people have been burning large amounts of coal, oil, and gas for energy. • Burning these fuels can pollute the air with sulfur, carbon, and nitrogen compounds. • Such compounds react chemically with the water vapor in clouds, forming acids. • These acids mix with raindrops and fall as acid rain. • Acid rain causes very rapid chemical weathering

13. Rate of Weathering • The most important factors that determine the rate at which weathering occurs • Type of rock • Climate

14. Permeable Rocks • Some rock weathers easily because it is permeable. • Permeable means that a material is full of tiny, connected air spaces that allow water to seep through it. • Permeable rock weathers chemically at a fast rate

15. Climate • How does climate contribute to weathering? • Climate refers to the average weather conditions in an area. • Both chemical and mechanical weathering occur faster in wet climates. • Chemical reactions occur faster at higher temperatures.