Understanding Weathering and Soil Formation: A Look at the Great Sphinx and Desert Soil, Schemes and Mind Maps of Topography

Download Understanding Weathering and Soil Formation: A Look at the Great Sphinx and Desert Soil and more Schemes and Mind Maps Topography in PDF only on Docsity! Mechanical Weathering Objectives Students will be able to: • Explain how weathering breaks down rock. • Explain how a rock’s surface area affects the rate of weathering. Mechanical Weathering – When physical processes naturally break rocks into smaller pieces, mechanical weathering occurs. – The chemical makeup of a rock stays the same during mechanical weathering. – Mechanical weathering can be caused by ice wedging, abrasion, plants, and animals. Surface Area – When something is broken into smaller pieces, it has a greater surface area. – Surface area is the amount of space on the outside of an object. Ice Wedging One of the most effective weathering processes is ice wedging—also called frost wedging. Water enters cracks in rocks. When the temperature reaches 0°C, the water freezes. Water expands as it freezes and the expansion widens the crack. As shown in the photo, repeated freezing and thawing can break rocks apart. CoS) MU Ce AU aati: Plants Plants can cause weathering by crumbling rocks. Imagine a plant growing into a crack in a rock. As the plant grows, its stem and roots not only get longer, they also get wider. The growing plant pushes on the sides of the crack. Over time, the rock breaks. Abrasion Another effective mechanical weathering process is abrasion—the grinding away of rock by friction or impact. For example, a strong current in a stream can carry loose fragments of rock downstream. The rock fragments tumble and grind against one another. Eventually, the fragments grind themselves into smaller and smaller pieces. Glaciers, wind, and waves along ocean or lake shores can also cause abrasion. Animals Animals that live in soil create holes in the soil where water enters and causes weathering. Animals burrowing through loose rock can also help to break down rocks as they dig. • Do you think the structures in these images have always looked like this? • What do you think caused these structures’ appearances to change? Chemical Weathering – Chemical weathering changes the materials that are part of a rock into new materials. – These granite obelisks show how chemical weathering can affect some rock. Chemical Weathering by Water – Water is important in chemical weathering because most substances dissolve in water. – The process of dissolving breaks up the minerals in the rock into small pieces. – The small pieces mix with water to form a solution and are washed away from the rock. Chemical Weathering by Oxidation – Oxidation combines the element oxygen with other elements or molecules. – The product of oxidation is called an oxide. – Oxides are useful because they form ores, which people use to obtain metals. – Do you know what the common term for iron oxide is? – Do all parts of an iron-containing rock oxidize at the same rate? Weathering rates – Weathering depends on water and temperature. – Mechanical weathering occurs fastest in areas that have a lot of temperature changes. – Chemical weathering is fastest where the climate is warm and wet, near the equator. Soil Components Engagement Which came first? Two friends were wondering which came first—soil or rock. This is what they said: Jenna: I think soil came first. Eventually it combines, hardens, and forms rock. Arnie: I think rock came first. Eventually the rock wears down and forms soil. Which student do you agree with? Explain. What is Soil? – Soil is a mixture of weathered rock, decayed organic matter, mineral fragments, water, and air. – About half the volume of soil is solid materials and the other half is liquids and gases. – Soil contains gases that fill the soil pores–the small holes and spaces in soil. – Why are pore spaces in soil needed to support the animals and plants that live in it? What is Soil? – We discussed before that weathering gradually breaks down rocks into smaller fragments. – What is the difference between sediment and soil? Soil Formation & Horizons Objectives Students will be able to: • Identify evidence of chemical weathering. • Explain how chemical weathering changes rock. • Differentiate between chemical and mechanical weathering. Wildflowers can bloom in all sorts of places, including the desert. Plants need many things to survive, including water and sunlight. But in the desert, as elsewhere, the composition of soil determines whether or not plants will grow. The plants shown here can grow in desert soil, but not on solid rock. 1. Describe the soil of a desert. How does it compare to the soil where you live? 2. Why is it difficult for most plants to grown on a solid rock? 3. Do you think that all plants could grow well in desert soil if you added water? Factors that Affect Soil Formation: Topography • Topography is the shape and steepness of the landscape. • The topography of an area determines what happens to water that reaches the soil surface. • Water running downhill can carry soil with it, leaving some slopes bare of soil. Factors that Affect Soil Formation: Biota • Biota is all of the organisms that live in a region. • Biota in the soil help speed up the process of soil formation in various ways. • Organisms can be involved in decomposition of organic matter or form passages in soil for water to move through. • Rock and soil are affected by organism activity. • Mature soils develop layers as new soil forms on top of older soil. Factors that Affect Soil Formation: Time • As time passes, weathering is constantly acting on rock and sediment. • This means soil formation is a constant, but slow process