Plate TectonicsMr. Q and Mrs. Wolfe

6th Grade Earth Science

What is Plate Tectonics?

• Theory that earth’s crust is broken into plates that float on the upper part of the mantle.

What causes plate tectonics?

• Convection Currents in the mantle

Continental drift – theory that the continents were at one or more times a single landmass that broke apart and eventually moved into the positions they are in today.

Quick Review

• Plate Tectonics: The Earth’s Crust is Broken into plates that Float on the mantle

• Continental Drift: The earth’s Continents were once one piece that have floated away.

• Alfred Wegener – Scientist who came up with the Theory of Continental Drift.

Pangaea – The name of the First single landmass created by Alfred Wegener. http://www.youtube.com/watch?v=ryrXAGY1dmE

• Evidence for Continental Drift

1. Earth’s continents look like puzzle pieces.

2. Fossils (remember Mesosaurus?)

3. Mountain ranges on different continents appear to match-up.

4. Rocks – of one continent match those along another continent.

• There are two (2) kinds of crust:

• Oceanic Crust (ocean)• Continental Crust (land)

• Mid-Ocean ridge: ocean-floor feature resembling a mountain. (New Sea Floor)

• Rift valley: flat area between two ridges that is formed by spreading plates.

• Seafloor spreading: process that forms new sea floor. (happens at Mid ocean Ridge)

http://www.youtube.com/watch?v=ryrXAGY1dmE

• New Seafloor is close to the Mid-Ocean Ridge…older floor is Farther away. (DUH!)

• Subduction Zone: A place where old oceanic crust is forced back down into an ocean trench and back into

the mantle

• A TRENCH is a deep ocean canyon. ( Subduction zones are found here)

• Many volcanoes and earthquakes are found near subductions zones. (ring of fire)

Evidence of Seafloor Spreading

• Fossils• Magnetic strips

What are some effects of Plate

Tectonics?

Earthquakes

Earthquakes

1906 and 1989 San Francisco earthquake was caused by the

movement of tectonic plates at the San Andreas Fault.

Mountain Building• When two plates collide such a collision

can cause the continental plate to crumble, and rise upwards – thus forming mountains.

Volcanoes

• At subduction zones, oceanic plates dip back down into the hot mantle.

• Heat from the mantle melts the rocks in the plate, forming magma.

• Magma collects in underground pockets called magma chambers.

• Hotter than the surrounding rock, the magma rises to the surface.

Volcanoes

Volcanoes

Hot Spot – place where magma

reaches the surface of a tectonic

plate. The Hawaiian islands

were formed this way.

• THE END (for now)