18Review: Physical Weathering Animals and insects loosen and break apart rocks in the soil.When water freezes in a crack of a rock it expands and makes the crack bigger.Plant roots enter cracks in rocks and as they grow force the cracks apart.As erosion moves material from the surface of a rock, pressure on the rock is reduced. This release of pressure causes it to crack and flake off like the layers of an onion.Sand and other rock particles that are carried by wind, water, or ice can wear away exposed rock surfaces like sandpaper on wood.Animal ActionsFreezing & ThawingPlant GrowthRelease of PressureAbrasion
19Chemical WeatheringThe process that breaks down rock through chemical changes.
23OxygenIron combines with oxygen in the presence of water in a processes called oxidationThe product of oxidation is rust, making rocks soft and crumbly.
24Carbon Dioxide CO2 dissolves in rain water and creates carbonic acid Carbonic acid easily weathers limestone and marble.Sink holes
25Carbon DioxideAlabamaThe Great Blue Hole: BelizeArizona
26Living OrganismsAs plant roots grow they produce weak acids. that dissolve the rock around the roots. Lichens that grow on rocks also produce weak acids.
27Acid RainCompounds from burning coal, oil and gas react chemically with water forming acids.Acid mixes with raindrops and cause very rapid chemical weathering of rock.
28Review: Chemical Weathering Water weathers rock by dissolving it.Iron combines with oxygen in the presence of water in a processes called oxidation or rust, making rocks soft and crumbly.CO2 dissolves in rain water and creates carbonic acid which easily weathers limestone and marble.As plant roots grow they produce weak acids. that dissolve the rock around the roots. Lichens that grow on rocks also produce weak acids.Compounds from burning coal, oil and gas react chemically with water forming acids. Acid mixes with raindrops and cause very rapid chemical weathering of rock.WaterOxygenCarbon DioxideLiving OrganismsAcid Rain
29How Fast Does Weathering Occur? The 2 most important factors that determine the rate at which weathering occurs are the:1. Type of rock (what a rock is made of) – Certain rocks and minerals are naturally weaker than others, while others are more resistant (stronger).2. The climate - Warmer, moister climates have the most weathering. Heat & Water speed up all chemical reactions. This is the most important factor in weathering.