Chapter 4: Weathering and Soil Formation

1. Chapter 4: Weathering and Soil Formation

2. SWORD WORD • Weathering – is a mechanical or chemical process that causes rocks to change by breaking them down into small pieces.

3. Weathering • Weathering is the breaking down rocks into smaller pieces either chemically or mechanically. • Example : holes in the roads and cracks in the sidewalk

4. Types of Weathering • There are 2 types of weathering, Mechanical and Chemical.

5. Mechanical Weathering • Mechanical Weathering is when rocks are broken down into smaller pieces without changing them chemically. • These pieces are the SAME as the original rock. • Two main causes are: Ice Wedging and Living Organisms.

6. Ice Wedging • Ice Wedging is • Water seeps into the cracks of rocks • Cold Temperature cause the water to freeze • Freezing water puts pressure on the rocks • Temperatures increase causing thawing – which melts the water and the rocks break apart. • Ice Wedging occurs when temperatures are constantly increasing and decreasing

7. Organic Matter (Plants and Animal) • Plants can grow in unlikely places. • Sometimes roots grow deep into cracks of rocks where water collects. • This puts pressure on the rocks and slowly pulls them apart.

8. Organic Matter (Plants and Animals) • Gophers and Prarie Dogs – These animals burrow through the ground, these animals break rock apart.

9. Chemical Weathering • Chemical Weathering occurs when the chemical composition of rocks change. • MOST COMMON in tropical regions where its mostly warm. • Two important causes: Natural Acids and Oxygen.

10. Natural Acids and Plant Acids • Natural Acids – when water mixes with carbon dioxide you get Carbonic Acid which can change the chemical composition of minerals in rocks. • Plant Acids – Many plants produce a substance called tannin. When water and tannin mix, it forms tannic acid. Tannic acid can dissolve rocks and break the remains into smaller pieces.

11. Oxygen • When you see a rusty car, red soil, or red stains on rocks you are seeing Oxidation. • Oxidation – is the effect of chemical changes causes by oxygen. • This involves iron containing minerals and oxygen, leaving it weak and it can break.

12. Soil • What is Soil??? • Soil is a mix of weathered rock, organic matter, water and air that supports growth of plant life. • Organic Matter means rotted leaves, twigs and roots

13. Soil Formation • Things that affect soil formation • Parent Rock • Slope of the Land • Climate • Time • Organisms

14. Soil Formation • Parent Rock – The type of rock originally weathered • Slope of the Land – The topography, or surface features of the land also influence the types of soil that forms. • Steep Hills – soil has little chance of forming. Why? Rock fragments are always moving downhill.

15. Soil Formation • Climate – If rock weathers rapidly, deep soils can form quickly. • Climate also affects the amount of organic material in soil. • Dead plants and animals eventually create humus, which helps soil hold water and provide nutrients for plants

16. Soil Formation • Time – As soil develops, they become less like the rock from which they are formed. • Organisms – Lichen are small organisms that consist of alga and a fungus. They grow directly on the rock. • As they grow, they take nutrients from the rock that they are breaking down and form thin soil.