Plate Tectonics Mrs. Ramsey 6 th Science

Inside the Earth Composition of earth: Divided into three layers – Crust: km think. Thinnest layer – Mantle- thicker than crust, contains most of earth’s mass. – Core- makes up 1/3 of earths mass

Inside the earth Physical structure of the earth – Lithosphere- outermost layer; made of crust and mantle – Asthenosphere- plastic layer where lithosphere moves – Mesosphere- strong lower part of mantle – Outer core- liquid layer of earth’s core that surrounds inner core – Inner core- solid and dense center of planet

Inside the earth Tectonic plates Think of lithosphere as “Giant jigsaw puzzle” Major tectonic plates – 1. Pacific plate – 2. North American plate – 3. Cocos plate – 4. Nazca plate – 5. South American plate – 6. African plate – 7. Eurasion plate – 8. Indian plate – 9. Australian plate – 10. Antarctic plate

Inside the Earth Some tectonic plates have both oceanic and continental crust. Look at pg 195 for reference. Answers about our earth’s core sometimes come from earthquakes. When a earthquake happens seismic waves are produced resulting in vibrations. Their speed depends on density and composition of what they are traveling through. Seismograph can measure seismic waves

The Theory of Plate Tectonics Plate tectonics is the theory to explain how plate tectonics move Boundary- place where tectonic plates touch Three types – Convergent- move towards – Divergent- move away – Transform- move past

The Theory of Plate Tectonics Convergent boundaries: Three types- continential-continential boundaries, Continential-oceanic boundaries, and oceanic- oceanic boundaries. Divergent boundaries: mid ocean ridges most common type. Transform boundaries: San Andreas fault good example

The Theory of Plate Tectonics San Andreas Fault

Theory of Plate Tectonics

The Theory of Plate Tectonics Possible Causes of Tectonic Plate motion – Ridge Push- oceanic lithosphere slides downhill under force of gravity – Convection- causes oceanic lithopshere to move sideways and away from the mid ocean ridge – Slab Pull-edge of tectonic plate that contains oceanic lithosphere sinks and pulls the rest of the tectonic plate with it.

The Theory of Plate Tectonics Movement is measured in centimeters a year.

Restless Continents Alfred Wagner- scientist who looked at world as “pieces of puzzle” He wrote hypothesis of continental drift. Continental drift- explains why fossils of same plant and animal species are on different sides of Atlantic Ocean

Restless Continent Breakup of Pangaea- Pangaea is Greek of “all earth” Gradual breakup- see Figure 2 Pangaea is the huge piece of land that Wagner believe was once all connected Laurasis and Gondwana are the two continents that Pangaea split into once it begin to move

Restless Continents Mid ocean ridges are underwater mountain chains where sea floor spreading takes place. Evidence for sea-floor spreading: magnetic reversal. North and south magnetic poles have changed place many times. Magnetic reversals are recorded in molten rock when grains of magnetic materials align with Earth’s magnetic field

Earthquakes Earthquakes are the shaking of earths ground. Seismology: Study of earthquakes MOST earthquakes occur near edges of tectonic plates. How do earthquakes occur? Faults: Break in the earth’s crust Deformation: bending, tilting, and breaking of the earth’s crust. Plastic deformation does NOT lead to earthquakes, but elastic deformation does

Earthquakes Elastic rebound- the sudden return of elastically deformed rock to its undeformed shape Energy is released during elastic rebound. Some energy travels in seismic waves which causes an earthquake

Earthquakes Plate motion Plate MotionMajor Fault type TransformStrike slip fault ConvergentReverse fault DIvergentNormal fault