Transcript Plate Tectonics

Plate Tectonics
A Whole Lot of Shakin’ Goin’ On
Layers of the Earth - Review
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Crust
Mantle
Outer core
Inner core
http://www.ccsf.edu/Departments/History_of_Time_and_Life/content/EarthLayers.htm
Review - Mapping the Earth’s Interior
• Scientists have gained the majority of
their knowledge about the inner parts of
the Earth from earthquakes.
• Earthquakes produce seismic waves which
travel through the Earth at different
speeds, depending on the material they
pass through.
• Seismographs measure the difference in
the waves’ arrival times, which let
scientists know the density of the material
the waves passed through.
The Crust
• The crust is the
outermost layer of
the earth
• It is made of two
types of crust
• Continental (35-100
km)
• Oceanic (5-10 km)
• It is not very thick
• 5-100 km thick
• We have only drilled
about 5 miles (8 km)
into the crust
• It’s a solid
• Where we live
http://www.sirinet.net/~project/MeersEarthsCrust.html
http://www.dlt.ncssm.edu/TIGER/diagrams/basics/ElementsInEarthsCrust.gif
• Convection – hot rises, cold sinks
Other Names
• Crust and upper mantle – lithosphere
• Where the tectonic plates are found
• Bottom of the upper mantle – asthenosphere
• Where the convection cells are
• Lower mantle - mesosphere
http://www.visionlearning.com/library/modules/mid69/Image/VLObject-1630-030917010902.gif
What are tectonic plates?
•Tectonic plates are pieces of the crust that
move around on top of the mantle.
•There are ten major tectonic plates.
•The tectonic plates form a “jigsaw puzzle”
like structure.
http://www.acmecompany.com/stock_thumbnails/11997.world_plates.gif
Restless Continents
•If you were to remove
all of the oceans from
the Earth and move the
continents together,
they would fit together
like a jigsaw puzzle.
•Is this a coincidence?
NO!
•If you try to put them
back together, there’s
only 1% that doesn’t fit
right!
http://www.scarborough.k12.me.us/wis/teachers/dtewhey/webquest/nature/images/pangaea%20fitting%20together.gif
Wegener’s Theory of Continental Drift
• It is the theory that
continents can drift apart
from one another and have
done so in the past.
• Wegener’s proof was fossils
of the same plant or animal
found on both sides of the
Atlantic Ocean. Many of
these species couldn’t
make it across the ocean.
• Continental drift also
explained similar glacial
patterns found on different
continents.
http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part5.html
http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_pics/F1.4.gif
Evidence of Pangea
The Breakup of Pangaea
• Wegener thought that all of
the continents of today were
once joined together about
245 million years ago in a
single supercontinent called
Pangaea.
• Around 180 million years
ago, Pangaea split into two
big pieces, called Laurasia
and Gondwana.
• 65 million years ago,
Laurasia and Gondwana split
into the current continents.
http://volcano.und.nodak.edu/vwdocs/vwlessons/plate_tectonics/part2.html
The Breakup of Pangaea
Sea-Floor Spreading
• Many scientists did not accept Wegener’s
theory. Wegener could not explain what
force caused the continents to drift apart.
• Sea-floor spreading answers that
question. Sea-floor spreading is the
process by which new oceanic crust is
created (by magma) as older materials are
pulled away.
• The crust increases in age the farther it
gets from the mid-ocean ridge formed by
the process.
Sea Floor Spreading
Sea-Floor Spreading
http://www.shenet.org/middle/acadia/bmoses/bm%20images/seafloor%20spreading.jpg
http://hal.physast.uga.edu/~jss/1010/ch14/ridge.jpg
Theory of Plate Tectonics
• The Theory of Plate Tectonics replaced
Wegener’s theory.
• This theory states that the Earth’s crust is
divided into tectonic plates that move around
on top of the mantle.
http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part12.html
Possible Causes of Plate Motion
•There are three possible causes of
motion, they are diagramed below.
Tectonic Plate Boundaries
• Convergent – Occurs when two
tectonic plates push into one another.
The three types of convergent
boundaries are
continental/continental,
continental/oceanic, and
oceanic/oceanic.
• Divergent – Occurs when two tectonic
plates move away from one another.
Mid-ocean ridges are the most
common divergent boundary, but they
can also be found on continents.
• Transform – Occurs when two tectonic
plates slide past one another
horizontally. The San Andreas Fault is
a good example
of a transform boundary.
http://volcano.und.edu/vwdocs/vwlessons/plate_tectonics/part13.html
What happens when these plates move?
• Convergent plate boundaries form
mountains.
• Divergent plate boundaries cause
volcanoes.
• Transform plate boundaries cause
earthquakes.
Tectonic Plate Boundaries
Tectonic Plate Boundaries
Different Types of Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.htm
Tracking Plate Motion
• The speed at which plates move depends
• the type and shape of the plate
• the way it interacts with the plates that surround it.
• The movement is generally so slow that you can’t see
or feel it. It is measured in centimeters per year.
• The exception is the San Andreas Fault, which moves
in jerks and jolts. These jerks and jolts cause
earthquakes.
• Scientists use the Global Positioning System (GPS) to
measure the movement of the tectonic plates. Radio
signals are sent from the Earth to orbiting satellites,
measuring the distance between the two. Over time,
the distances change slightly.
http://www.geologie.ens.fr/~vigny/images/gps-cours3.jpg
Review
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Name the 3 main layers of the Earth
What is a tectonic plate?
What was Pangea?
What is Sea-Floor spreading?
Name the three different types of plate
boundaries and one location on Earth for
each one