How do tectonic plates move? Notes How do tectonic plates move?

Continental Drift Alfred Wegener (1915) Continental Drift Pangaea

Evidence for continental drift: Fossils Climate Geology

? Problem: Wegener could not explain HOW the continents moved. Continental Drift ? Problem: Wegener could not explain HOW the continents moved.

Sonar Technology (World War I) New Evidence in the 1950’s Sonar Technology (World War I) Uses sound to measure distance underwater Like echolocation in bats!

Scientists used sonar to map the ocean floor. New Evidence in the 1950’s Scientists used sonar to map the ocean floor. Led to the discovery of the mid-Atlantic ridge.

Other discoveries: Underwater volcanos Geothermal vents Hot springs New Evidence in the 1950’s Other discoveries: Underwater volcanos Geothermal vents Hot springs Deep ocean trenches

Plate Tectonics The theory of plate tectonics builds on Wegener’s ideas but also explains HOW the plates and continents move.

Plate Tectonics Harry Hess (1906-1969) Discovered that rock on the seafloor is younger near a mid- ocean ridge and older further away from the ridge

Plate Tectonics

Plate Tectonics New crust is being created in the middle of a mid-ocean ridge, where two tectonic plates are being pushed apart.

Cracks in Earth’s crust are the tectonic plate boundaries. Plate Tectonics Cracks in Earth’s crust are the tectonic plate boundaries. Magma rises through the crack, pushes the two plates a little further apart, and cools to form new crust.

Driving Forces Remember-tectonic plates float on the asthenosphere-a layer of hot, soft rock.

Convection: transfer of (heat) by movement of a substance. Driving Forces Convection: transfer of (heat) by movement of a substance. Convection is what happens when you boil a pot of water.

The water at the bottom heats up, becomes less dense and rises. Driving Forces The water at the bottom heats up, becomes less dense and rises. Near the surface, it cools, becomes more dense, and sinks.

Driving Forces Rock in the asthenosphere acts the same way as a boiling pot of water-it moves by convection.

Driving Forces When this rising and sinking repeats, it creates a circular pattern called a convection current.

Driving Forces The movement of the mantle is much slower than a pot of boiling water-only a few centimeters per year!

Driving Forces The movement of the asthenosphere is like heavy boxes on rollers-but moving very, very slowly.

Driving Forces Slab Pull: when gravity pulls the edge of a cool plate into the asthenosphere.

Driving Forces Ridge Push: when material from a mid-ocean ridge slides downhill from the ridge.

Putting it All Together There are several tectonic plates on Earth. One plate cannot shift without affecting the others nearby. Two neighboring tectonic plates can either move apart, move together, or slide past one another.

Putting it All Together Divergent boundary: plates move apart

Putting it All Together Convergent boundary: plates move toward each other

Putting it All Together Transform boundary: plates slide past each other