Earth Science
Plate Tectonics
Essential Question
• What is the history of Plate Tectonics?
• What are the mechanisms?
Geosphere
Use the plate tectonics theory
to explain features of
the earth’s surface and geological phenomena,
and describe evidence
for the plate tectonics theory.
Key concepts
Earth Composition
Crust: The Earth’s Skin, outer layer
Mantle: upper part is able to
flow very slowly
Core: interior at high temperature
and pressure
starryskies.com/.../Earth/ under_the_surface.html
Key concepts
Evidence of “continental drift”—
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•Physical fit of continents
•Fossil evidence
•Measurements of movement
•Rock layer sequences
•Glacial evidence
Alfred Wegener
What is the theory of continental drift?
• the idea that the continents were once all joined
together in one super-continent called Pangaea
and slowly moved to their current positions
http://wrgis.wr.usgs.gov/docs/parks/animate/A08.gif
What evidence supports the
theory of continental drift?
Shoreline Fit of the Continents
http://www.abdn.ac.uk/zoohons/lecture1/img008.GIF
Fossil Evidence
The fossils from the exact same animals are found on
continents separated by vast oceans.
Matching Rock Layers
Glacier Evidence
Glaciers scars are found on continents
which are today too warm for glaciers.
How fast are the plates moving?
Essential Question:
You may wonder…
Why are the
continents moving?
Seafloor Spreading
The oceans are widening along the
mid-ocean ridges.
Volcanoes located along ocean ridges
erupt, creating new ocean floor.
Key concepts
Plates—continental crust, oceanic crust
Features—faults, trenches, mid-ocean
ridges, folded mountains, hot spots, volcanoes
Related actions —earthquakes, volcanic
activity, seafloor spreading, mountain building,
convection in mantle.
Three Types of
Plate Boundaries
• Divergent
• Convergent
• Transform
The earth’s lithosphere is broken into huge
sections called plates that are in constant motion.
What are the plates made of?
• Ocean plates are
made of basalt.
• Continental plates
are made of granite.
Divergent Plate Boundaries
Two land or ocean plates move apart in opposite
directions. Magma flows to the surface between
them creating new crust.
Mid-Atlantic Ridge = Divergent Boundary
http://www.geo.lsa.umich.edu/~crlb/COURSES/270/Lec12/spreexamples.jpeg
Iceland – a continent directly
over the Mid-Atlantic Ridge
Subduction Zones
• An ocean plate and a continental plate hit head-on.
The ocean plate subducts under the continent
forming a trench. The subducting plate melts.
Magma rises to the surface creating a string of
volcanic mountains parallel to the shoreline.
Andes Mountains
Subduction zones form chains of
volcanic mountains along the shoreline.
Collision Zones
Two continents hit head-on, crinkling up the
land into a high mountain chain.
India’s Collision with Asia
Himalayas
The Himalayas Are Born…
Island Arcs
Two ocean plates hit head-on. One ocean plate is forced
to subduct under the other forming an ocean trench.
The subducting plate melts. Magma rises to the surface
forming a string of volcanic islands parallel to the trench.
The Aleutian
Islands
Key concepts
Forces—tension, compression shearing
Ask a Geologist
Ask an earth scientist
How does tectonic activity affect
the earth’s crust?
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Builds mountains
Creates deep ocean trenches
Causes earthquakes
Create volcanoes
Ocean Trenches
http://www.nhusd.k12.ca.us/ALVE/wow/Ocean/seafloor.gif
Volcanoes
Most volcanoes occur at plate boundaries…
http://www.thirteen.org/savageearth/hellscrust/assets/images/ringoffire.jpg
Real-world contexts:
Recent patterns of earthquake and volcanic activities;
maps showing the direction of movement of major plates
and associated earthquake and volcanic activity
Compressional boundaries: folded mountains, thrust faults,
trenches, lines of volcanoes (e.g. Pacific “ring of fire”)
Tensional boundaries: mid-ocean ridges, rift valleys
Shearing boundaries: lateral movement producing
faults (e.g. San Andreas Fault).
http://www.gfz-potsdam.de/pb2/pb22/projects/mamba.html
Resources
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http://www.calstatela.edu/faculty/acolvil/plates/pangaea.jpg
http://platetectonics.pwnet.org/img/wegener.jpg
http://home.tiscalinet.ch/biografien/images/wegener_kontinente.jpg
http://library.thinkquest.org/17457/platetectonics/comic.jpg
http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/images/fossil_c
orrelation_lge.jpg
http://earthobservatory.nasa.gov/Library/Giants/Wegener/Images/plate_bou
ndaries.gif
http://www.calstatela.edu/faculty/acolvil/plates/atlantic_profile.jpg
http://pubs.usgs.gov/publications/graphics/Fig16.gif
http://cps.earth.northwestern.edu/SPECTRA/IMG/basalt.png
http://cc.usu.edu/~sharohl/granite.jpg
http://tlacaelel.igeofcu.unam.mx/~GeoD/figs/tgondvana_ice.jpg
http://www.physics.uc.edu/~hanson/ASTRO/LECTURENOTES/F01/Lec11/
Pangaea.gif
http://www.poleshiftprepare.com/glacial_striation.jpg
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http://www.ggs.org.ge/plates.jpg
http://earth.geol.ksu.edu/sgao/g100/plots/1008_world_volc_map.jpg
http://www.aeic.alaska.edu/Input/affiliated/doerte/personal/aleutians/ak_ma
p_big.jpg
http://www.4reference.net/encyclopedias/wikipedia/images/Aleutians_aerial.
jpg
http://www.avo.alaska.edu/gifs/2-3/02-95-03.jpg
http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/images/island_a
rc.jpg
http://nte-serveur.univlyon1.fr/nte/geosciences/geodyn_int/tectonique2/himalaya/images/Fig5a_in
de.gif
http://terra.kueps.kyoto-u.ac.jp/~sake/himalaya.jpg
http://www.andes.org.uk/peak-info-5000/sabancaya.jpg
http://www-step.kugi.kyoto-u.ac.jp/~keizo/photos/andes.JPG
http://www.letus.northwestern.edu/projects/esp/top10/andespage/andesphy
sical.jpg
• http://www.soc.soton.ac.uk/CHD/classroom@sea/carlsberg/images/
atlantic_tectonics%20.jpg