Earth Science

Weathering Section 7.1 Notes Earth Science

I. Mechanical Weathering i. Weathering: the process in which materials on or near Earth’s surface break down and change. ii. Mechanical weathering: rocks and minerals break down into smaller pieces. Also called physical weathering. iii. Physical change of rocks b. Effects of temperature i. Water freezes and melts causing cracks in rocks ii. Water expands 9% when frozen iii. Frost wedging: freeze-thaw cycles break apart rocks c. Effect of pressure i. Roots of trees and plants exert pressure on rocks ii. They act as a wedge in the rocks breaking them apart iii. Pressure within earth 1. when overlying rocks are removed so is the pressure 2. the once buried rock begins to expand 3. long curved cracks occur in bedrock with this expansion iv. Exfoliation: outer rock is stripped away from under layers 1. results in dome shaped formations II. Chemical Weathering i. The process by which rocks and minerals undergo changes in their composition. ii. Agents of chemical weathering 1. Water 2. Oxygen 3. Carbon dioxide 4. Acid precipitation iii. Chemical reactions occur in rocks and minerals iv. Rocks and minerals composed of calcite react strongly with acid precipitation v. Temperature – significant factor 1. Affect rate chemical interactions occur 2. Rate of chemical weathering reactions double with each 10 degrees Celsius increase b. Effect of Water i. Important agent in chemical weathering ii. Can dissolve many kinds of rocks and minerals. iii. Serves as a medium in which reactions can occur iv. Can react directly with minerals v. When large molecules of a mineral break into smaller ones with water present, the mineral decomposes into many silicate minerals. c. Effect of Oxygen i. Chemical reaction of oxygen with other substances is called oxidation. ii. Common mineral that contains the oxidized form of iron is hematite. d. Effect of carbon dioxide i. When combined with water in atmosphere, it forms a weak acid called carbonic acid ii. Precipitation includes 1. rain 2. snow 3. sleet 4. fog iii. the acidity causes precipitation to dissolve certain rocks. iv. Decaying organic matter emits large amounts of carbon dioxide v. When acid precipitation lands on this matter, carbonic acid begins to dissolve rocks such as calcite in limestone and marble. e. Effect of acid precipitation i. Caused by sulfur dioxide, carbon dioxide, and nitrogen oxides. ii. These are results of human activities- burning fossil fuels iii. Acid precipitation ha s pH value below 5.6 iv. Many plant and animals are affected by the acid precipitation in addition to structures. III. Rates of weathering