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Download Dynamic Earth Interactive Notes Earth`s Structure Plate Tectonics
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Transcript
Dynamic Earth Interactive Notes Objectives: [8.9A] Describe the historical development of evidence that supports plate tectonic theory. [8.9B] Relate plate tectonics to the formation of crustal features. Earth’s Structure Cross Section Plate Tectonics Alfred Wegener – suggested that the Earth’s continents were once joined together in one large mass he called Pangaea using the following evidence: o Coastlines of Africa and South America fit together o Same plant and animal fossils on coastlines o Similar geologic features on both coastlines Plate Tectonic Theory – States that Earth’s outer layer, or lithosphere, is broken into several large slabs called plates. Plates and Boundaries - Continental Crust – Crust that makes up the continents. (20-40 miles thick) Oceanic Crust – Crust that makes up the ocean floor. (4-6 miles thick) Boundary – Border between two tectonic plates 3 types of Plate Boundaries Convergent Boundary Divergent Boundary Transform Boundary Slip, Slide and Collide Convergent Boundaries Subduction Zones and Volcanoes Form when oceanic crust is involved Lithosphere – Rigid outer layer of the Earth broken up into tectonic plates. Asthenosphere – Hot, semi-liquid zone of the mantle on which the tectonic plates float. Subduction Zone – The area where one plate is being pulled under the edge of another plate at a convergent boundary. Trench – a deep oceanic trench, or valley, that forms at a subduction zone as the oceanic crust sinks under the other tectonic plate. Island Arcs – Chains of volcanoes that form at the subduction zone in the ocean between two oceanic plates. Tsunami – a huge ocean wave caused by a sudden shift on the ocean floor, such as an undersea earthquake. Collision Zones and Mountains Form when only continental crusts collide. Continental crust is less dense than oceanic crust therefore does not subduct and causes the rock to crunch and fold upwards forming mountains. An example is the Himalayan mountain range where the continental crust of the Indian plate is colliding with the continental crust of the Eurasian plate. Divergent Boundaries – Spreading Plates Tectonic plates are moving away from each other. In Oceans: Seafloor Spreading – Occurs at divergent boundaries in the middle of the oceans at features called mid-ocean ridges where oceanic crust is pulled apart as magma comes up from the mantle forming new oceanic crust. On Land: Rifts – Valleys that form when two continental plates move apart at divergent boundaries. Transform Boundaries – Grinding Plates Tectonic plates grind past each other in a horizontal direction forming a fault – a crack or fracture in the earth’s crust that is associated with this movement. Faults and Earthquake Faults produce many earthquakes, the shaking and trembling of the earth’s crust caused by the sudden movement of plates as they build up stress at transform boundaries. These are called Strike-Slip Faults. Example – San Andreas Fault in California