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Plate Tectonics Location of earthquakes since 2000 M>3 Volcanoes Locations Topographic and Barometric map Shows elevations Continental Drift theory Alfred Wegener (1912) Continental Drift theory Alfred Wegener (1912) - He postulated that all landmasses were originally united into a supercontinent named Pangaea. - Pangaea consisted of a northern landmass called Laurasia and a southern landmass called Gondwana. - As Pangaea broke up, the various continents moved to their present-day locations. What is the Evidence for Continental Drift? • Evidence 1: Fossil Evidence – Some of the most compelling evidence comes from fossils like the Glossopteris fern. – One of the strongest examples is the Mesosaurus, a fresh water reptile. What is the Evidence for Continental Drift? • Evidence 2.Similarity of Rock Sequences and Mountain Ranges – Marine, nonmarine, and glacial rock sequences of old age (Jurassic) are nearly identical on all the Gondwana continents Fig. 2.4, p. 32 What is the Evidence for Continental Drift? • Evidence 3. Glacial Evidence – Glacial tills and striations on the bedrock beneath the till provide evidence of glaciation at the same time on all the Gondwana continents, with South Africa located at the South Pole. Earth’s Magnetic Field • Paleomagnetism is the remnant magnetism in ancient rocks recording the direction and intensity of Earth’s magnetic field at the time of the rock’s formation. Fig. 2.8, p. 35 Earth’s Magnetic Field – Evidence 4 Paleomagnetic studies during the 1950's revived interest in continental drift – The continents had moved over time. If the continents were moved into different positions relative to each other, the separate poles could be resolved into one. Fig. 2.9, p. 36 Earth’s Compositional Layers Atmosphere & Hydrosphere Crust Mantle Core Lithosphere & Asthenosphere Earth’s Tectonic Plates What moves the plates? Convection cells The Three Types of Plate Boundaries • Types of Plate Boundaries – Divergent – Convergent – Transform http://www.iris.edu/hq/programs/education_and_outreach/animations/11 • B1. Divergent Boundaries – Form when plates move away from one another. • New oceanic lithosphere is forms at the opening rift. Red means younger! • B2. Convergent Boundaries. Places where two plates collide • B3. Transform Boundaries – These are boundaries along which plates slide laterally past each other along transform faults Fig.4.22a Formation of Volcanic Chain ation of Island Chains V1 lithosphere melting at base of crust V1 V1 Hot (not molten) rising plume Fig.4.22b Example: The Hawaiian Chain Fixed hot spot Basic Premise of Plate Tectonics • Earth’s crust is divided into plates • Plates move relative to one another (at 1-15 cm/yr) • Deformation is concentrated at plate boundaries • There are 3 types of tectonic boundaries Consequences: • Plate tectonics constantly change Earth’s surface • Earthquakes occur mostly at plate boundaries • Volcanoes occur mostly at plate boundaries