Plate tectonics

Tectonic Plates

Plate Tectonics

• Greek – “tektonikos” of a builder• Pieces of the lithosphere that move around• Each plate has a name• Fit together like jigsaw puzzles• Float on top of mantle similar to ice cubes

in a bowl of water

Continental Drift

http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml

Alfred Wegener 1900’sContinents were once a single land mass that drifted apart.

Fossils of the same plants and animals are found on different continents

Called this supercontinent Pangea, Greek for “all Earth”

245 Million years ago

Split again – Laurasia & Gondwana 180 million years ago

Evidence of Pangea

Sea Floor Spreading

Sea Floor Spreading

• Mid Ocean Ridges – underwater mountain chains that run through the Earth’s Basins

• Magma rises to the surface and solidifies and new crust forms

• Older Crust is pushedfarther away from the ridge

Why do plates move?

Convection currents

Convection currents• What are they?• How do they make plates move?• When mantle rocks near the radioactive core are heated, they

become less dense than the cooler, upper mantle rocks. These warmer rocks rise while the cooler rocks sink, creating slow, vertical currents within the mantle (these convection currents move mantle rocks only a few centimeters a year). This movement of warmer and cooler mantle rocks, in turn, creates pockets of circulation within the mantle called convection cells. The circulation of these convection cells could very well be the driving force behind the movement of tectonic plates over the athenosphere.

Subduction

• What is it?• One plate sinks underneath the other because

it is more dense.

How Plates Move

http://pubs.usgs.gov/gip/dynamic/unanswered.html

Convection currents

• Destructive vs. Constructive forces• Define both of the terms below:• Constructive forces- builds the Earth up• Destructive forces- Breaks the Earth down

Destructive or constructive?type destructive constructive both

Erosion

Weathering

Deposition

Volcano

earthquake

Different Types of Boundaries

http://pubs.usgs.gov/gip/dynamic/understanding.html

Plate boundaries

• Transform• Plates slide past each other• Earthquakes form

Transform Boundary – San Andreas Fault

www.geology.com

Plate boundaries

• Divergent• Plates divide• In ocean- will be mid-ocean ridges• On land- rift valleys• Why? As plates spread apart, magma rises

through the gap and forms new crust

Divergent Boundary – Arabian and African Plates

Arabian Plate

African PlateRed Sea

Divergent Boundary – Iceland

http://pubs.usgs.gov/gip/dynamic/understanding.html

Divergent Boundary - Oceanic

http://www.geology.com

Divergent Boundary - Continental

http://www.geology.com

Convergent Boundary – Indian and Eurasian Plates

Indian Plate

Eurasian Plate

Convergent Boundary – Oceanic & Continental

http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Plate boundaries

• Convergent• Plates collide (go together)• When ocean plates meet continent plates, an

ocean trench forms with volcano on the land• Why? Ocean plate is more dense than

continental and sinks under it into mantle (subduction)

Convergent Boundary – Oceanic & Oceanic

http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

NOTE – PLATES ARE REVERSED

Plate boundaries

• Convergent• Plates collide (go together)• When ocean plates meet ocean plates, an

ocean trench forms with magma forming islands

• Why? The ocean plate that is more dense will sink under the other (subduction)

Convergent Boundaries - Continental

http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com

Plate boundaries

• Convergent• Plates collide (go together)• When continent plates meet continent plates, mountains form Why? Continental plates buckle up as they

push together

Plate tectonic animations

• http://www.nature.nps.gov/geology/usgsnps/animate/pltecan.html

Additional activities:

• Plate tectonics www.brainpop.com• Volcanoes

http://www.brainpop.com/science/earthsystem/volcanoes/

• Earthquake http://www.brainpop.com/science/earthsystem/earthquakes/

• Pangaea activity worksheet• Plate boundary prediction worksheet