pg. 47/48 Plate Tectonics

Pangaea Continental drift caused the supercontinent Pangaea to separate Pangaea -Greek word meaning ‘all the earth’; most recent supercontinent Theory proposed by Alfred Wegener Evidence from similar rock formation and fossil remains found on two different continents Coal deposits in Antarctica indicate the climate was once warm and temperate Was initially rejected because there was no reason why the continents were moving

Seafloor spreading Harry Hess credited with the discovery of seafloor spreading Seafloor was once thought to be flat and unchanging Technology has proved otherwise Sonar –uses reflecting sound waves Magnetometer- detects changes in magnetic fields; measured strength of rocks magnetic field Magma creeps up and creates new seafloor close to the ocean ridge As new magma breaks through, older parts spread out

Ocean Floor Topography Maps were made containing ocean ridges Volcanoes and earthquakes common near ridges Also found trenches Largest trench is the Mariana Trench in the Pacific Ocean (11 km deep)

Ocean floor and magnetism Scientists found the ages of rocks and thickness of rocks increased the further away from ocean ridges. Used paleomagnetism to map the rocks and sediments Basalt is commonly used to record magnetism Revealed magnetic reversals Using data from magnetic reversals, scientists were able to create an isochron

Theory of plate tectonics Earth’s crust and mantle are broken into enormous slabs called plates Tectonic plates interact at plate boundaries Some converge, others diverge, some move horizontally past one another

Divergent Boundaries Most are found on seafloor; form ocean ridges Located in a rift, or fault bounded valley Associated with high volcanic activity, earthquakes, and high heat Divergent boundaries on continents create a rift valley Long narrow depression

Convergent boundary 3 types Oceanic crust converging w/ oceanic crust One of the plates descends under another in a process called subduction Can form islands Oceanic converging w/ continental crust Subduction occurs Produces a trench and volcanic arc Continental converging w/ continental Mountain ridges form

Transform Boundary Place where 2 plates slide past one another Crust is deformed and fractured Characterized by long faults and small earthquakes