Chapter 5 Notes: Plate Tectonics Earth s Interior Scientists learn about the interior of Earth in 2 ways o Direct Method Rock Samples Drilling Caves o Indirect Method Seismic Waves Speed of waves and paths shows the structure of the planet o Show that the earth is made up of several layers The Layers of the earth vary in several ways Temperature o Gets warmer as you descend toward the center of the earth Temperature rises 1 o C for every 40 meters descended Pressure o Pressure increases as you descend The Layers of the Earth The Crust o Outer Layer Includes dry land Includes the ocean floor Includes Water and soil o Thinner than other layers Thinnest under oceans Called oceanic crust o Composed of BASALT Thickest under mountains Called continental crust o Composed of Granite The Mantle o 40 Km below surface o Hot Solid Rock o About 3000 km thick o Divided into layers Lithosphere Upper part of mantle Rigid Layer Asthenosphere
Below lithosphere Hotter Increasing pressure Softer but still solid Lower Mantle Under Asthenosphere Solid- extends to the core The Core o Made of iron and Nickel o Has 2 parts Outer Core Liquid Molten(melted) metal surrounding inner core Inner Core Dense ball Solid metal o Creates a Magnetic Field Due to movement in the core Magnetic poles Convection and Mantle Types of Heat transfer Radiation: transfer of energy through space o No direct contact between heat source and object o Examples The sun Fire Conduction: heat transfer within a material or between materials that are touching o Responsible for some of the heat transfer within the Earth o Example: metal spoon in a hot pot Convection: heat transfer by the movement of currents in a fluid o Caused by differences in temperature and densities in a fluid o Examples Convection zone in the sun Deep currents in ocean Convection Currents in Earth Mantle o Heat from the mantle causes convection current Moves the plates of the lithosphere Core o Heat in the outer (liquid) core causes a convection current Causes Earth s magnetic field
Continental Drift Alfred Wegner o Thought all continents formed Pangaea at one time Pangaea: a single land mass Evidence Shape of the continents Fossils o Glossopteris Climate o Wegener s theory was rejected He could not explain the forces that push and pull the continents Sea Floor Spreading Mid Ocean Ridges Tall mountain ridges hidden under the oceans o Curve around the world In a few places the ridge or mountain is above the surface of the ocean Example: Iceland Mapped using Sonar o Sonar is a device that bounces sound waves off underwater objects and then records the echoes of the sound waves Sea Floor Spreading Sea floor spreads apart along both sides of the mid ocean ridge o Adds New Crust o Ocean floor like a conveyor belt Carries continents Evidence of Sea Floor Spreading o Molten material Submarine Alvin finds pillow shaped rocks These rocks only form when molten material cools quickly o Magnetic strips The earth s magnetic poles have reversed many times Evidence in the rocks on the ocean floor o Drilling Samples The samples far from the ridge are older The youngest rocks near the center of the ridge
Subduction at Trenches Process by which ocean floor sinks under the trench and back into the mantle o Crust near ridge moves away from ridge Like a giant conveyor belt The ocean floor o Pacific Ocean is shrinking Lots of deep trenches Trench swallows more of the floor faster than its made o Atlantic Ocean expanding Oceanic crust attached to the continental crust Continents move Theory of Plate Tectonics J. Tuzo Wilson Scientist who discovered the plates o Plates: a section of the lithosphere that slowly moves over the Asthenosphere carrying pieces of the continental and oceanic crust Combined continental drift and sea floor spreading into a scientific theory o Scientific Theory: well tested concept that explains a wide range of observations Ideas that are supported by data. How Plates Move Theory of Plate Tectonics o Earth s lithosphere is in constant, slow motion driven by the convection currents in the mantle. 3 ways of moving o Collide (convergent) o Pull apart (divergent) o Grind past each other (transform) Each changes the earth s surface Plate Boundaries Extend deep into the lithosphere o Faults: breaks in Earth s crust where rocks have slipped past each other Move Slowly
3 kinds of Boundaries Divergent Boundaries o Plates move away from each other o Most occur along the mid ocean ridge Where sea floor spreading occurs o Can occur on land Forms a Rift Valley A deep valley Convergent Boundaries o Two plates that come together or collide o Density of the plates determine which plate is on top Oceanic crust vs. continental crust Subduction. Continental crust vs. continental crust Mountains are squeezed from the crust Transform Boundaries o 2 plates slip past each other Earthquakes are common o Crust is neither destroyed or created