What we know…What we know…

Wegener collected evidence and Wegener collected evidence and proposed the theory of proposed the theory of Continental Continental DriftDrift..

Hess found the “mechanism” to Hess found the “mechanism” to support the idea with his theory of support the idea with his theory of Sea-Floor SpreadingSea-Floor Spreading..

Put the two together… we get the Put the two together… we get the Theory Theory of Plate Tectonicsof Plate Tectonics..

Plate TectonicsPlate Tectonics The Earth’s crust and rigid upper mantle are The Earth’s crust and rigid upper mantle are

broken into huge slabs called tectonic broken into huge slabs called tectonic plates (about a dozen major plates, and plates (about a dozen major plates, and several smaller ones).several smaller ones).

Tectonic plates interact at places Tectonic plates interact at places called called plate boundaries.plate boundaries.

This is where MOST of the action is This is where MOST of the action is really taking place. really taking place.

Divergent BoundariesDivergent Boundaries The place where two tectonic plates are pulling away from The place where two tectonic plates are pulling away from

each other (not always, but usually occurs on the seafloor).each other (not always, but usually occurs on the seafloor). A common feature associated with a divergent boundary is A common feature associated with a divergent boundary is

a a ridge/rift.ridge/rift. A good example of a divergent boundary is the A good example of a divergent boundary is the Mid-Mid-

Atlantic Ridge.Atlantic Ridge.

Another Picture of a Divergent Another Picture of a Divergent Boundary – A Mid-Ocean RidgeBoundary – A Mid-Ocean Ridge

Arguably the best example of a divergent Arguably the best example of a divergent boundary – The Mid-Atlantic Ridgeboundary – The Mid-Atlantic Ridge

Convergent BoundariesConvergent Boundaries : : The place where two tectonic plates are pushing against each The place where two tectonic plates are pushing against each

other. other. – Oceanic/Continental: Basalt/Granite (a trench and a Oceanic/Continental: Basalt/Granite (a trench and a

continental arc are formed)continental arc are formed)– Oceanic/Oceanic: Basalt/Basalt (a trench and an island arc are Oceanic/Oceanic: Basalt/Basalt (a trench and an island arc are

formed)formed)– Continental/Continental: Granite/Granite (folded mountains Continental/Continental: Granite/Granite (folded mountains

are formed)are formed)

Convergent Boundaries Cont…Convergent Boundaries Cont… A common feature associated with a convergent boundary A common feature associated with a convergent boundary

is a is a subduction.subduction. A good example of a convergent boundary is the A good example of a convergent boundary is the Mariana Mariana

Trench / Mariana IslandTrench / Mariana Island..

Transform BoundariesTransform Boundaries The place where two tectonic plates are sliding past one The place where two tectonic plates are sliding past one

another.another. A good example of a transform boundary is the A good example of a transform boundary is the San Andres San Andres

Fault in CaliforniaFault in California..

More Photos of the San Andreas More Photos of the San Andreas FaultFault

The San Andreas near San FranciscoThe San Andreas near San Francisco

… … in Central Californiain Central California