Plate Tectonics. 6-1 Continental Drift Continental Drift theory that the continents were once a...

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