Plate Tectonics

Definitions

Asthenosphere - A portion of the Earth’s mantle underneath the lithosphere that can flow

Continental Drift - The theory that the continents have moved in position over time

Lithosphere - Earth’s rigid outer zone, made up of tectonic plates

Tectonic Plate - A section of the Earth’s lithosphere

Mantle - Earth’s middle layer

Mid-ocean Ridge - A long chain of mountains under the ocean formed by plate tectonics

Rift Valley - A valley formed when a continent is being pulled apart

Subduction - When one tectonic plate moves underneath another

Convergent Boundary - Where two tectonic plates are moving towards each other

Divergent Boundary - Where two tectonic plates are moving away from each other

Transform Boundary - Where two tectonic plates are sliding past one another

Fault - A break in the Earth’s surface where blocks of rock slide past each other

Fold Mountain - A mountain formed by the folding of continental crust when tectonic plates collide

Convection - The transfer of heat by movement of a liquid or gas

Slab Pull - When a tectonic plate is pulled across the mantle towards the subduction zone


Alfred Wagner’s Theory of Continental Drift

  • Continents had once been joined as one large land mass called Pangea

Supporting Evidence

  • Evidence found for glacial climates in Equatorial Africa and tropical climates in Northwest Europe

  • Continental shelves fit together like pieces of a jigsaw

  • Identical rock formations on either side of the Atlantic Ocean

  • Identical plant and animal fossils on different continents separated by oceans


The seafloor is spreading apart

  • Spreading occurs when molten rock rises up from the mantle at the mid-ocean ridges

Supporting Evidence

  • Rift valleys along mid-ocean ridges

  • Magnetic stripping

  • Depth of sediments

  • Age of seafloor


Old lithosphere is subducted

  • Subduction occurs when the edge of one tectonic plate is pushed under the one next to it

Supporting Evidence

  • Ocean trenches

  • Earthquake locations get deeper the further they are from ocean trenches

  • Volcano chains above zones


Ridge push is caused by gravity

  • Ridge push happens at mid-ocean ridges

  • When magma rises up the mid-ocean ridge, it forms a new lithosphere

  • This new lithosphere sits higher than the old lithosphere, and so gravity causes it to move downhill

  • This push helps to move the tectonic plate along, away from the ridge and towards the subduction zone


Convection Currents

  • Convection is a way to move heat

  • This transfer happens when a fluid, like air or water, is in motion

  • Convection is driven by temperature differences across that fluid

  • The portion of fluid that is less dense then rises