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Transcript
Environmental Science Unit 1: Geology Basics Earth’s Layers & Plate Tectonics 1 2 Lithosphere vs Asthenosphere • Lithosphere: Crust + upper Mantel – 80 km deep (50 miles) – Less dense than Asthenosphere – Floats on the Asthenosphere – Plates move slowly! 2”/yr • Asthenosphere: – Fluid part of Mantel—ductile, like putty – Underneath the Lithosphere 3 Shape of Earth’s Surface • Main force: Movement of Earth’s outer layer by the process of: – PLATE TECTONICS • What is a “tectonic plate”? – Earth’s crust is made up of ~12 “plates” that fit together like a jigsaw puzzle. • Plates have continental and ocean crust. • Plates move around, causing: Earthquakes, Volcanoes, Mountain Building, and much of the Rock Cycle. 4 Processes that change Earth’s surface: • Weathering & Erosion – Weathering • Chemical • Physical – Wind – Water • Volcanism • Deformation 6 Plate Movements • Converging Plates – plates moving together, form trenches • Diverging Plates – Plates moving apart, form mid-oceanic ridges 7 What is “Subduction” ? • Two sections of crust collide – One slab is forced down deep into Earth 8 Volcanism • Bring Magma to the surface 9 Volcanism • The most general cause of volcanism on earth is Subduction of earth’s crust. – One tectonic plate is forced under another plate as the plates push together. 10 11 Mid-Ocean Ridges • Bottom of sea splits apart: – Magma rises – New Crust formed • “Spreading Ridges” – Lithosphere slides away from elevated region • 4 cm/yr – Central portions of oceans 12 Rifting • Continents can also split apart at “rifts”. – Continued rifting can form a new ocean. Chemical Weathering • Minerals in rocks are dissolved into rainwater or • changed from one type of mineral into another. Occurs most readily in warm, moist areas. – Warm speeds up chemical reactions. – Water is required for chemical weathering. • Minerals differ in their resistance to chemical weathering. – Quartz resists chemical weathering. – Feldspar does not resist well. • Breaks down into clay minerals. Chemical Weathering • Ever been to a cave? – Caverns develop as water flows underground, dissolving minerals in rock and transporting them away. • Cave features, such as stalactites and stalagmites form when mineral-carrying water drips and leaves behind some of its mineral load. 15 Cave • Stalactites “Hang on tight” to the ceiling. – Form as minerals come out of water as a drip forms. • “Mighty” Stalagmites – Form as minerals come out of water after it drips to the floor. Physical Weathering • Rocks are broken apart into smaller pieces by water and other forces. – Moving liquid water can break rock apart by knocking rocks together. • Rivers, Ocean surf, etc. – Glaciers break, grind, and move rock. – Water can break rock as it freezes in cracks. • Water expands as it freezes, and can exert tremendous forces. Potholes in roads and exploding soda cans show the power of freezing water. Soil • Bits of broken rocks + remains of plants & animals 19 Soil • Soil Horizon – Each layer of soil in a soil profile • Soil Profile – The arrangement of the layers of soil in an area 20 What is a “Fault” ? • Fracture due to stress on rock • Cause: pushing & shoving of crust: – Seafloor spreading 21 22 Making Mountains 23 Making Mountains • Folding – Colliding plates—neither is subducted – Plates crash and rise vertically 24