Plate Tectonics Year 7 Science PDF

Plate tectonics Year 7 Science Continental Drift In 1915, Alfred Wegener claimed that the Earth’s continents were once connected to each other and that over time the continents had separated and drifted apart. Continental Drift He called the single supercontinent Pangaea. Which over time split i...

Plate tectonics Year 7 Science Continental Drift In 1915, Alfred Wegener claimed that the Earth’s continents were once connected to each other and that over time the continents had separated and drifted apart. Continental Drift He called the single supercontinent Pangaea. Which over time split into two land masses, Laurasia (the northern continent) and Gondwana (the southern continent) Evidence of Continental Drift Wegener based his conclusions on two main observations. - The continents seemed to fit together like a jigsaw puzzle That fossils of the same species were found on continents that were a long way apart. Tectonic plates The crust is made up of a number of moveable lithospheric plates sitting and moving along the molten asthenosphere below What scientific evidence do we have that these cracks in the crust exist? Seafloor spreading Studies of the ocean floor discovered the presence of large underwater mountain ridges running around the Earth. These ridges were found to have huge series of rifts (cracks) in their centres. It has been described as the Great Global Rift System, Seafloor spreading Seafloor spreading Harry Hess, an American geologist proposed that new rocky crust was being formed at the ocean ridges and spreading outwards. He also proposed that the crust was sinking down into the Earth in ocean trenches through the process of subduction. When combined, seafloor spreading and subduction are involved in the creation and destruction of the crust. Convection currents in the mantle ● ● As magma in the mantle is heated, it becomes less dense and rises. Once it reaches the crust the magma then travels along the underside of the solid crust until it cools down, becoming more dense. This causes the magma to sink back down. This movement of magma is thought by some scientists to play a role in the movement of the continents. How plates move Theory 2: Ridge push and slab pull Types of crust Oceanic crust ● ● ● ● ● 5 – 10 km thick More dense Tiny Crystals Very hard rock Contains heavier elements e.g. iron, magnesium Continental crust ● 25 – 100 km thick ● Less dense ● Larger crystals ● More easily eroded ● Contains lighter elements e.g. aluminum, silicon Type of plate movement