Plate Tectonics
6-1 Continental Drift Continental Drift theory
that the continents were once a single land mass that broke apart
Pangaea supercontinent
Evidence of Continental Drift
South America & Africa look like they fit together
Fossils of mesosaurus found in S. America & Africa
Evidence of Continental Drift cont.
6-2 Seafloor Spreading
2 types of crustContinental
○Less denseOceanic
○More dense
6-2 cont. Mid-ocean ridge
underwater mt. chain in the oceans
Rift crack Rift valley flat area
btw. ridges
6-2 cont. New seafloor magma rises up through a rift
Magma cools making new crust
New crust pushes floor apart at ridges
6-3 Evidence of Seafloor Spreading Trench deep canyons
in the ocean floor Most in the Pacific Ocean
Old crust ends up in trenches
Melts & becomes magma again
6-3 cont. Subduction zone area
where crust is forced down in trenches
Youngest fossils = closest to rift valleys, ridges, & trenches
6-4 Plate Tectonics Tectonic plates the
lithosphere broken into pieces
7 major plates & 8 minor plates
Asthenosphere liquid part of the mantle
6-4 cont. Theory of Plate
Tectonics explains how & why plates (continents) moveLithosphere floats on asthenosphere
6-5 Plate Tectonics Convection current less
dense warm rises & denser cool sinks
3 types of plate boundariesConvergentDivergentTransform
6-5 cont.
Transform 2 plates sliding past each other Cause earthquakes
6-5 cont.Convergent 2 plates move toward each other○Oceanic + continental = oceanic subducts under the continental
○Continental + continental = mountain
6-5 cont.
Divergent 2 plates move away from each otherCause rift valleysCause seafloor spreading
6-6 Effects of Plate Tectonics Earthquakes plates
slide past each other at a fault
Mountains plates collide & buckle upward
6-6 cont. Volcanoes oceanic plate
dips down & magma collects
Hot spots place where magma reaches the surface
Islands plates move over hot spots & volcanoes build
