Plate Tectonics

1. Plate Tectonics By Leanne

2. How The Theory was discovered. Plate tectonic theory arose out of the hypothesis of continental drift proposed by Alfred Wegener in 1912[and expanded in his 1915 book The Origin of Continents and Oceans. He suggested that the present continents once formed a single land mass that drifted apart, thus releasing the continents from the Earth's core and likening them to "icebergs" of low density granite floating on a sea of denser basalt. But without detailed evidence and a force sufficient to drive the movement, the theory was not generally accepted: the Earth might have a solid crust and a liquid core, but there seemed to be no way that portions of the crust could move around. Later science supported theories proposed by English geologist Arthur Holmes in 1920 that plate junctions might lie beneath the sea and Holmes' 1928 suggestion of convection currents within the mantle as the driving force.

3. Theory of Plate Tectonics - Continental Drift • Earths outer shell is composed of plates --> • they move at a rate of about 3 cm per year • affect of more land at higher latitudes: • alter ocean currents and therefore heat transport • alter global atmospheric circulation • more glaciers over land, higher albedo, cooler temperatures. • plate movement also generates more volcanic activity • hence, when the plates are on the move, have more volcanic eruptions -> emit more CO2 into the atmosphere, • this would cause global temps to rise. • if there is little movement, volcanic activity decreases -> so CO2 concentrations are lower in the atmosphere -> average temp decreases.

4. Earthquakes The Richter magnitude scale assigns a single number to measure the amount of seismic energy released by an earthquake. An earthquake is the result of a sudden release of energy in the Earth’s crust that creates seismic waves. The epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. In the case of earthquakes, the epicentre is directly above the point where the fault begins to rupture, and in most cases, it is the area of greatest damage. However, in larger events, the length of the fault rupture is much longer, and damage can be spread across the rupture zone.