Unit 2 Lesson 1 Weathering Copyright © Houghton Mifflin Harcourt Publishing Company 1

Unit 2 Lesson 1 Weathering Florida Benchmarks SC.6.E.6.1 Describe and give examples of ways in which Earth’s surface is built up and torn down by physical and chemical weathering, erosion, and deposition. LA.6.2.2.3 The student will organize information to show understanding (e.g., representing main ideas within text through charting, mapping, paraphrasing, summarizing, or comparing/contrasting). Copyright © Houghton Mifflin Harcourt Publishing Company 2

Break It Down What is weathering? Unit 2 Lesson 1 Weathering Break It Down What is weathering? Weathering is the breakdown of rock material by physical and chemical processes. Two kinds of weathering are physical weathering and chemical weathering. Copyright © Houghton Mifflin Harcourt Publishing Company 3

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Physical weathering is the process by which rock is broken down into smaller pieces by physical changes. The composition of the material does not change during physical weathering. Agents of physical weathering include temperature changes, pressure changes, plant and animal actions, water, wind, and gravity. Copyright © Houghton Mifflin Harcourt Publishing Company 4

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Changes in temperature can cause a rock to break apart by weakening the structure of the rock. Heat causes expansion. Cold causes contraction. Ice wedging, or frost wedging, causes cracks in rocks to widen with repeated cycles of freezing and thawing. Copyright © Houghton Mifflin Harcourt Publishing Company 5

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? How can a small crack in a rock eventually split the rock into two or more pieces? Copyright © Houghton Mifflin Harcourt Publishing Company 6

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Rocks that formed under deep pressure can be exposed to the surface. Pressure changes can cause the rock to expand as material is removed above the rock. Exfoliation is the process by which the outer layers of rock slowly peel away due to pressure changes. Copyright © Houghton Mifflin Harcourt Publishing Company 7

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Animals can cause physical weathering by digging burrows. New rock material and soils become exposed to the surface as a result of animal actions. Copyright © Houghton Mifflin Harcourt Publishing Company 8

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Abrasion is the breaking down and wearing away of rock material by the mechanical action of other rocks. Three agents of physical weathering that can cause abrasion are moving water, wind, and gravity. Copyright © Houghton Mifflin Harcourt Publishing Company 9

What causes physical weathering? Unit 2 Lesson 1 Weathering What causes physical weathering? Roots of plants can grow in a small crack in a rock, causing it to be wedged apart over time. As roots grow, more pressure is put on rock, causing expansion. Copyright © Houghton Mifflin Harcourt Publishing Company 10

Reaction What causes chemical weathering? Unit 2 Lesson 1 Weathering Reaction What causes chemical weathering? Chemical weathering is the breakdown of rocks by chemical reactions. Chemical weathering changes both the composition and appearance of rocks. Agents of chemical weathering include oxygen in the air and acids. Copyright © Houghton Mifflin Harcourt Publishing Company 11

What causes chemical weathering? Unit 2 Lesson 1 Weathering What causes chemical weathering? Oxidation is the process by which other chemicals in rock combine with oxygen in the air. Rock surfaces can change color during oxidation, indicating a chemical reaction may have occurred. Copyright © Houghton Mifflin Harcourt Publishing Company 12

What causes chemical weathering? Unit 2 Lesson 1 Weathering What causes chemical weathering? Acids can cause chemical weathering by breaking down minerals faster than water alone. Acids in the atmosphere are created when chemicals combine with water in the air. Acid precipitation occurs when strong acids fall to Earth as rain, sleet, or snow. Copyright © Houghton Mifflin Harcourt Publishing Company 13

What causes chemical weathering? Unit 2 Lesson 1 Weathering What causes chemical weathering? Water in the ground can cause chemical weathering. Acids in groundwater can cause rock to dissolve. Dissolved chemicals in groundwater can be deposited in new locations over time. Copyright © Houghton Mifflin Harcourt Publishing Company 14

What causes chemical weathering? Unit 2 Lesson 1 Weathering What causes chemical weathering? Acids in living things can cause chemical weathering. Chemical reactions occur as acids produced naturally by living things move through rock material. Acids can break down rocks. Copyright © Houghton Mifflin Harcourt Publishing Company 15