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
Alfred Wegener 1900’s
Continents 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
http://members.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml
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 pushed
farther 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
Erosion
Weathering
Deposition
Volcano
earthquake
destructive
constructive
both
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
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
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
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