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The Changing Earth. Relative aging, fossils, natural disasters. Erosion. Rocks breaking down into smaller pieces. Runoff. Water that moves over Earth’s surface Causes sheet erosion Moves downhill Forms rills and gullies. Rivers.
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The Changing Earth Relative aging, fossils, natural disasters
Erosion • Rocks breaking down into smaller pieces
Runoff • Water that moves over Earth’s surface • Causes sheet erosion • Moves downhill • Forms rills and gullies
Rivers • Erosion creates valleys, waterfalls, flood plains, meanders, oxbow lakes • Deposition creates alluvial fans, deltas, add soil to flood plain
Groundwater • Underground water • Chemical weathering-water combines with CO2 to form carbonic acid, breaks down limestone • Forms caves, stalactite (roof) and stalagmite (floor)
Glaciers • Continental glaciers-covers much of continent, island • Valley glaciers-long, narrow glacier from snow and ice in mountain valley
Glaciers • Plucks rocks • Breaks rocks • Drags rocks which scratches bedrock • Deposits sediment when it melts- till, moraine, kettle
Waves • Energy comes from wind blown across water’s surface • Break apart rocks on shore • Abrasion-headland, arch, cave • Deposit sediment-beaches, spits, sandbars, barrier beaches
Wind • Deflation-wind removes surface materials, Dust Bowl • Abrasion-Polishes rock, little erosion • Deposits-sand dunes, loess-sediment that is finer than sand
Loose, weathered material on Earth’s surface in which plants can grow. Soil
Rock broken down by weathering • Sediment mixes with materials on surface • Soil horizon-layer of soil that is different in color and texture Soil Formation
Topsoil- crumbly, dark soil that is a mixture of humus, clay, and other minerals • Subsoil-Clay, other particles, little humus Soil Layers
Humus-formed from organic material • Litter-layer of dead plant leaves • Decomposers-break down organic matter to form humus • Earthworms, and other burrowing animals mix soil Living Organisms in Soil
Fertility-ability for plants to grow depend on nutrients in soil • Dust Bowl-loss of topsoil, devastating • Soil conservation by farmers Importance of Soil
Fossils • Preserved remains or traces of living things
How fossils form • Living things die and are buried in sediments • Sediments harden into rock and preserve shapes of organisms • Sedimentary rock
Molds and casts • Most common • Mold-hollow area in sediment in shape of organism • Cast-sold copy of the shape of organism
Petrified Fossils • Minerals replace all or part of an organism • Petrified wood
Carbon Films • Extremely thin coat of carbon on rock • Carbon from organism left behind in shape of organism
Trace Fossils • Provide evidence of activities of organisms • Footprints • Trails • Burrows
Preserved Remains • Organism trapped in tar, or amber • Rancho La Brea tar pits • Freezing in Siberia • Protects organism from decay
Relative Age of Rocks • Age compared to the age of other rocks • Absolute age-number of years since rock formed
Law of Superposition • In horizontal sedimentary rock layers, the oldest layer is at the bottom and each higher layer is younger than the layers below it.
Determining Relative Age • Extrusion- lava that hardens on the surface • Always younger than the extrusion below it • Intrusion- Magma that hardens into igneous rock • Always younger than the rock layers around and beneath it • Faults-Break in Earth’s crust • Younger than rock it cuts through • Unconformity- Gap in geological record • Rock layers lost because of erosion
Index Fossils • Tell relative ages of the rock layers in which they occur
Radioactive Dating • Atoms of one element break down to form atoms of another element • Half-life- time it takes for half of the radioactive atoms to decay • Carbon-14- measure amount of Carbon-14 left in organism to determine absolute age