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1-3 CHANGES ON THE EARTH’S SURFACE I. WEATHERING A. Weathering – breakdown of rock at or near the earth’s surface into smaller and smaller pieces B. Mechanical Weathering – occurs when rock is actually broken or weakened physically 1. breaks large masses of rock into smaller pieces (boulders, stones, pebbles, sand, silt, and dust) C. Chemical Weathering – alters a rock’s chemical makeup by changing the minerals that form the rock or combining them with new chemicals 1. can change one rock into a completely different type of rock 2. many caves are formed when acidic water seeps into cracks of rocks 3. acid rain – chemicals in the polluted air combine with water vapor and fall back to earth (destroys forests, pollutes water, eats away at stone buildings) EXAMPLES Mechanical Weathering Chemical Weathering II. EROSION A. Erosion – movement of weathered materials such as gravel, soil, and sand B. 3 most common causes of erosion: 1. water 2. wind 3. glaciers C. Important part of the cycle that has made and kept the earth a place where living things can survive A. WATER 1. Water is the greatest cause of erosion, because over time, water can cut into the hardest rock and wear it away 2. Water moving down a streambed carries sediment (small particles of soil, sand, and gravel)…that sediment helps grind away the surface of rocks 3. The rock and soil that is carried away with erosion eventually creates other landforms 4. The Mississippi River carries approximately 159 million tons of sediment a year 5. Crashing ocean surf causes steep bluffs, cliffs, or sand dunes B. WIND 1. Cause of erosion in areas where there is little water and few plants to hold the soil in place 2. In the Great Plains, the rich fertile soil that they once had was blown away by the wind during a drought…this area is now known as the “Dust Bowl” because they cannot grow anything there anymore 3. The wind can also deposit mineral-rich dust and silt called loess, which can help areas that once were barren 4. Sandstorms can cause erosion by carving or smoothing the surfaces of rock formations and man-made objects C. GLACIERS 1. Glaciers – huge, slow-moving sheets of ice 2. Form over many years as layers of unmelted snow are pressed together, thaw slightly, and then turn to ice 3. As glaciers move, they carry dirt, rocks, and boulders 4. The time periods where much of the earth is covered in glaciers are known as Ice Ages – geologists believe that we’ve had at least 4 5. Much of the U.S. was formed by glaciers (Great Lakes, Long Island, etc.) 6. Glaciers slide forward because of how heavy they are and only pieces of it move at a time (oozes) GLACIERS