Plate Tectonic Notes • Earth’s Layers: • Crust • Mantle • Core Earth’s Layers • Crust Lithosphere outermost layer that is the tectonic plates but does have some mantle rock • Mantle – 2 Parts Asthenosphere: (solid, soft layer that moves slowly) The layer that the tectonic plates move on Mesosphere: solid lower part of the mantle • Core – Outer core (liquid iron and nickel) – Inner core (solid iron and nickel) Earth’s plates Pangaea- Supercontinent that once existed on Earth around 245 million years ago… Plate Movement • Continental Drift – Lithosphere (tectonic plates) is divided into plates that slide around on top of the slowly moving asthenosphere – It occurred after the break-up of Pangaea, and since then the continents have drifted apart Theory of Continental Drift – Alfred Wegener (early 1900’s) was the first to discuss the theory of Pangaea and continental drift. – Theory of Pangaea- claimed that the continents had formed a single land mass which has split apart over time. – Wegner was not the first to suggest this theory, but he was the first to present information from several fields. – Continental Drift Theory – Was that all of the continents were once joined together, but over time have drifted apart., – Pangea – name of the supercontinent that contained all land on Earth Evidence of Continental Drift • Evidence of Wegner’s theory: – Similar glacier deposits in South America and Africa, and fossil findings – The outlines of the continents fit with each other. – Mountain ranges line up between Africa and South America. How does continental drift work? - Plates compress or pull apart from each other • Plates collide = convergent boundary • Plates separate = divergent boundary • Plates slide past one another horizontally = transform boundary • Subduction zone = one plate slides under another Convergent Boundary • Plates collide while moving towards each other • When both plates are continental plates, the plates push against each other, creating mountain ranges. Subduction Zone • When an oceanic plate slides under a continental plate. Cause: oceanic trenches, and can cause volcanoes to form due to the oceanic plate melting and creating pressure under the continental plate. Divergent Boundary • Plates separate (pull apart) When plates pull away from one another they form: sea floor spreading, mid-oceanic ridges or rift valleys Sea Floor Spreading Theory • Harry Hess formulated the idea of sea floor spreading in 1962. • Sea Floor Spreading Theory- idea that the seafloor moves and carries the continents with it. • Caused by divergent boundaries moving apart and allowing the liquid like asthenosphere to move upward and cool creating new oceanic crust. Transform Boundary • Plates slide past one another horizontally • These areas are likely to cause earthquakes, and volcanic action, and fault lines. What is the force moving Plate tectonics: CONVECTION CURRENTS - Convection currents in the mantle are what causes the movement of tectonic plates. - As the extremely hot molten material from the mantle rises toward the crust, it cools enough to become denser and sink back into the hotter area of the mantle. - The process repeats (cycles) continually. Rock does two things when stress is placed on it. It can fold or fault (break). When plates push against one another, they form MOUNTAINS. • Folded Mountains – made when rock is squeezed together and pushed upward Fault – broken rock layers resulting from stress • These mainly occur around transform boundaries • They are due to stress from tectonic plate movement. Ring Of Fire • 90% of the world's earthquakes and 89% of the world's largest earthquakes occur along the Ring of Fire in the Pacific Ocean from California around to India – Caused by subduction zones. .