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11/17/2016 1 Section 1: Weathering and Soil Formation Do Now: Why do you think soil is an important part of our ecosystem? 2 • Weathering: Mechanical or chemical surface process that breaks rocks into smaller pieces – Examples: • Freezing and thawing • Oxygen in the air • Plants and animals • These examples cause rock’s surface to weather, and in some cases become soil • 2 types of weathering: Mechanical and Chemical 3 1. MECHANICAL WEATHERING • Mechanical weathering is the breaking down of rock without changing them chemically. This is caused by ice, water, or wind (think naturally!) – Two main categories: • Ice wedging • Plants and Animals 4 Ice Wedging • Air temperature can drop low enough to FREEZE water, but when the air temperature rises, the water thaws • • • 5 Ice Wedging • When water seeps into cracks, the deeper the cracks are the deeper the water can get in. The water freezes (expands) breaking the cracks further. • • • 6 Plants and Animals • As trees grow, their roots grow deep into cracks in rocks where water collects. • As they grow, the roots become larger, causing pressure to wedge rock further apart. • • Animals that burrow in the ground break the rocks apart. • • 7 2. CHEMICAL WEATHERING • Chemical weathering is when the chemical composition of rock changes – Three main categories: • Natural Acids • Plant Acids • Effect of Oxygen 1 • 11/17/2016 7 2. CHEMICAL WEATHERING • Chemical weathering is when the chemical composition of rock changes – Three main categories: • Natural Acids • Plant Acids • Effect of Oxygen 8 Natural Acids • Carbonic acid: when water mixes with carbon dioxide in the air or soil • Carbonic acid changes the composition of the minerals in the rocks • Carbonic acid dissolves rocks 9 Plant Acids • Tannin ( from the roots of plants ) forms Tannic acid, which dissolves some minerals in rock • This causes the rocks to break into pieces 10 Effect of Oxygen • Oxidation: if the substance contains IRON, when it oxidizes it will rust. • • In Rocks, it turns the appearance a darker color, because rocks can contain iron. 11 SOIL • Soil: Mixture of weathered rock, organic matter, and air that supports the growth of plant life. • • Organic matter: decomposed leaves, twigs, roots, and other material 12 Factors that affect soil formation 1. Parent rock 2. Slope of land 3. Climate 4. Time 5. Organisms 13 1. Parent Rock • The soil type depends upon the type of rock it comes from – Example: Limestone causes clay-like soil 14 2. Slope of the Land • The TOPOGRAPHY (surface features) of an area influence the types of soils that develop. – Example: on a steep hill, soil has a little chance of developing because the pieces of rock roll downhill. 15 3. Climate • Affects the amount of organic material is in the soil – In deserts, the soil contains little organic material – In warm humid environments, the soil contains a lot of organic material • Why? –Because not a lot of plants live in the desert because of the lack of WATER. 16 3. Climate • Humus: the formation of a dark-colored material from fungi or bacteria after plants and animals die. 2 15 3. Climate • Affects the amount of organic material is in the soil – In deserts, the soil contains little organic material – In warm humid environments, the soil contains a lot of organic material • Why? –Because not a lot of plants live in the desert because of the lack of WATER. 16 3. Climate • Humus: the formation of a dark-colored material from fungi or bacteria after plants and animals die. • • Humus holds most of the organic matter, water, and provides nutrients for the soil. 17 4. Time • It can take THOUSANDS of years for rocks to weather. • As time passes, the soil becomes less like its’ parent rock. • If weathering is undisturbed, thick and well developed soil will form. 18 5. Organisms • Fungi, bacteria, and other types of decomposers create well developed soil. • The decomposers break down dead organisms and cause a thin layer of humus to form. This is enough soil for plant life to grow. 11/17/2016 3