Earth Science Week 20 PDF

Earth Science  Internal Structure of Earth  Learning Targets… Today I can… 1. Identify and differentiate the layers of Earth; 2. Describe the continental drift theory; 3. Discuss the evidence that support continental drift; 4. Explain how seafloor spread; 5. Describe the stru...

Earth Science  Internal Structure of Earth  Learning Targets… Today I can… 1. Identify and differentiate the layers of Earth; 2. Describe the continental drift theory; 3. Discuss the evidence that support continental drift; 4. Explain how seafloor spread; 5. Describe the structure and evolution of ocean basins; and 6. Explain how the movement of plates leads to the formation of folds, faults, trenches, volcanoes, rift valleys, and mountain ranges.  Continental Drift Theory Earth’s continents are not static; instead, they gradually migrate across the globe. Because of these movements, blocks of continental materials collide, deforming the intervening crust, thereby creating Earth’s great mountain chains.  Evidences 1. Fit of Continental Shorelines (Jigsaw Puzzle) 2. Distribution of Glacial Sediments 3. Paleoclimate 4. Distribution of Fossils 5. Distribution of Rocks PLATE TECTONIC BOUNDARIES  Plate Tectonics  The theory of plate tectonics The crust is the surface of the Earth. It is a rock layer forming the upper part of the lithosphere. The lithosphere is split into tectonic plates. Continental crust is typically 30-50 km thick. Oceanic crust is only 5-10 km thick. Oceanic crust is denser, can be subducted and is constantly being destroyed and replaced at plate boundaries. Continental crust is older, lighter and cannot be destroyed. The Earth's crust is broken into plates. Heat rising and falling inside the mantle creates convection currents generated by radioactive decay in the core. The convection currents move the plates. D I V E R G E N T A DIVERGENT BOUNDARY occurs when two tectonic plates move away from each other. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earth’s mantle to the surface, solidifying to create new oceanic crust.  Oceanic Ridges and Seafloor Spreading The majority of, but not all, divergent plate boundaries are associated with oceanic ridges: elevated areas of the seafloor characterized by high heat flow and volcanism. The mechanism that operates along the oceanic ridge system to create new seafloor is appropriately called seafloor spreading. Typical rates of spreading average around 5 centimeters (2 inches) per year, roughly the same rate at which human fingernails grow.  Continental Rifting Divergent boundaries can develop within a continent, in which case the landmass may split into two or more smaller segments separated by an ocean basin. Continental rifting begins when plate motions produce opposing (tensional) forces that pull and stretch the lithosphere. Because the lower lithosphere is warm and weak it deforms without breaking. As the tectonic forces continue to pull apart the crust, the broken crustal fragments sink, generating an elongated depression called a continental rift, which eventually widens to form a narrow sea and then a new ocean basin. C O N V E R G E N T When two plates come together, it is known as a CONVERGENT BOUNDARY. The impact of the colliding plates can cause the edges of one or both plates to buckle up into a mountain ranges or one of the plates may bend down into a deep seafloor trench.  Oceanic-Continental Convergence When the leading edge of a plate capped with continental crust converges with a slab of oceanic lithosphere, the buoyant continental block remains “floating,” while the denser oceanic slab sinks into the mantle.  Oceanic-Oceanic Convergence Where two oceanic slabs converge, one descends beneath the other, initiating volcanic activity by the same mechanism that operates at all subduction zones.  Continental-Continental Convergence The third type of convergent boundary results when one landmass moves toward the margin of another because of subduction of the intervening seafloor. T R A N S F O R M F A U L T Two plates sliding past each other forms a TRANSFORM PLATE BOUNDARY. Natural or human-made structures that cross a transform boundary are offset—split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. Earthquakes are common along these faults. In contrast to convergent and divergent boundaries, crust is cracked and broken at transform margins, but is not created or destroyed. The End