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Warm-Up A tree root is growing into rocks on the side of a hill. What do you think is happening and how will it affect the rocks? Weathering Earth’s Changing Surface Weathering, erosion and deposition act together in a cycle that wears down and builds up Earth’s surface. What is weathering? The process where rocks are broken into smaller rocks. What is mechanical weathering? Occurs when rocks are broken into smaller pieces by physical processes. …by plant activity Roots grow in cracks of rock – As roots grow, so does the crack …by animal activity Burrowing animals (worms, rabbits, etc.) create holes – Exposes more rock This picture shows prairie dogs burrowing into the soil. Note the small rocks that are now exposed. …by grinding of rocks (abrasion) Caused by wind, running water, waves, and gravity Rocks pushed together, causing pieces to chip away See how the wind has weathered this rock? Another example of abrasion – running water How can ice wedging break rocks? Water expands when it freezes. Liquid water seeps into rock cracks and freezes. …by ice wedging Water gets into cracks and freezes – Remember, water EXPANDS when it freezes – Causes cracks to get bigger Another picture of ice wedging Chemical Weathering What is chemical weathering? breakdown of rock through changes in its chemical makeup. – breaks down or weakens the rock – More rapid in warm, wet climates …by carbonation Carbon dioxide + water = carbonic acid – Carbonic acid reacts with minerals (like calcite) Rocks (like limestone) can be entirely dissolved, leaving extensive caverns – Can cause massive damage to structures above ground (ex: creating sinkholes) …by oxidation Oxygen + iron = iron oxide Iron oxide + water = rust If you compare a rusty nail to a regular nail, the unweathered nail is much stronger. …by acids From plants (when it decays) Acid rain – Normal rain is pH 6.2 – Sometimes rain can be at a pH of 4 due to pollution, factories, and coal burning plants True or False Ice wedging occurs because of animals. True or False Weathering is the process where rock is broken down. True or False Mechanical weathering creates rocks with new chemicals. True or False Animals that dig tunnels do not help to break down rocks. True or False Abrasion is the grinding of rocks against other rocks.