Plate Tectonics

Continental drift All continents were once connected as one large landmass called Pangaea. Landmass broke apart and drifted to their present positions.

Evidence for continental drift Puzzle-like fit of the continents Similar fossils have been found on different continents. Remains of warm weather plants found in arctic areas and glacial deposits found in tropical areas. Similar rock structures are found on different continents.

Seafloor Spreading Mid-ocean ridges- underwater mountain ranges discovered using sound waves. The theory of Seafloor spreading (Harry Hess) explained these ridges.

Hot, Less dense material below Earth’s crust rises upward to the surfaces at the mid ocean ridges. Then, it, flows sideways, carrying the seafloor away from the ridge. As the seafloor spreads apart, magma moves up and flows from the cracks, cools, and forms new seafloor.

Evidence for SFS Youngest rocks are located at mid-ocean ridges. Reversal of Earth’s magnetic field are recorded by rocks in strips parallel to ridges.

Discussion Question How could seafloor spreading be related to continental drift?

Answer If the Seafloor is constantly spreading apart and moving, it will effect and move the continents as well.

Theory of Plate Tectonics Earth’s crust and upper mantle are broken into sections called plates, they move on a plastic-like layer of the mantle. Plates and upper mantle form the lithosphere. Plastic-like layer below is called asthenosphere.

Plate Boundaries Divergent Plate boundaries Plates moving apart.

Convergent Boundaries Plates moving together. Denser plates sink under less dense plates. Newly formed hot magma forced upward forms volcanic mountains

Plates collide Plates crumple up to form mountain ranges. Earthquakes are common

Transform boundary Plates slide past one another. Sudden movement can cause earthquakes

Features caused by plate tectonics Convection inside the Earth is thought to be the force behind plate tectonics. Features caused by plate tectonics Faults and rift valleys Mountains and volcanoes Strike- slip faults – cause of earthquakes.