Transcript Plate Tectonics

Plate Tectonics
Liz LaRosa for use with my 5th Grade Science Class
http://www.middleschoolscience.com 2009
Earth’s Layers
The Earth's rocky outer
crust solidified billions of
years ago, soon after
the Earth formed.
This crust is not a solid
shell; it is broken up into
huge, thick plates that
drift atop the soft,
underlying mantle.
The Crust
• Outermost layer
• 5 – 100 km thick
• Made of Oxygen, Silicon,
Aluminum
The Mantle
• Layer of Earth
between the crust
and the core
• Contains most of
the Earth’s mass
• Has more
magnesium and
less aluminum and
silicon than the
crust
• Is denser than the
crust
The Core
• Below the mantle
and to the center of
the Earth
• Believed to be
mostly Iron, smaller
amounts of Nickel,
almost no Oxygen,
Silicon, Aluminum,
or Magnesium
Tectonic Plates
Plate Tectonics
• The theory of the formation and movement of the plates
that cover the Earth’s surface
• The earth is constantly changing. In addition to the effects
of weathering and erosion, there are much larger scale
changes occurring due to the movement of large plates in
the lithosphere.
• Each plate has a name and fit together like jigsaw puzzles.
• They float on top of the mantle similar to ice cubes in a
bowl of water
• In the 1930’s, Alfred Wegener proposed the idea that
continents were drifting.
• He could not successfully explain the force that could move
such massive amounts of material so his theory did not
gain acceptance.
Acceptance of Wegener’s Theory
• In the late 1950’s and early 60’s, evidence emerged that
suggested convection within the Earth’s asthenosphere
could be the driving force behind the movement of the
plates.
• Further investigations have led to wide spread
acceptance of the theory of plate tectonics.
• The interactions of the plate boundaries also help
explain the location of volcanoes and earthquakes. This
further supports the theory.
Continental Drift
•The theory that all continents
are fragments of Pangaea now
drifting apart is called 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/Contin
ents.shtml
Evidence of Pangea
Boundaries
• The plates interact in 3 different ways
called boundaries.
• The 3 types of boundaries are
– transform
– convergent and
– divergent
Different Types of Boundaries
http://pubs.usgs.gov/gip/dynamic/understanding.html
Convergent Boundaries
• At convergent boundaries the plates are crashing
into each other.
• If both plates are the same (oceanic/oceanic or
continental/continental) they push each other
upward in a process called uplift.
• If the plates are different (oceanic/continental) the
oceanic plate gets pushed beneath the continental
plate.
• As the oceanic plate gets pushed deeper into the
earth, the oceanic plate melts and the hot magma
rises to the surface forming a chain of volcanic
mountains.
Convergent Boundary – Indian and Eurasian Plates
Convergent Boundary – Oceanic & Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundaries - Continental
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Convergent Boundary – Oceanic & Oceanic
http://pubs.usgs.gov/gip/dynamic/understanding.html & http://www.geology.com
Divergent Boundaries
• Plates that are moving apart from each
other are called divergent.
• When continental plates separate, land
subsidence occurs.
– Subsidence is the motion the Earth's surface
as it shifts downward relative to sea-level.
• When oceanic crust moves apart, magma
rises to fill the space creating new oceanic
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
Transform Boundaries
• Transform boundaries happen when two
plates are sideswiping each other (in very
slow motion).
• Major earthquakes occur as these
boundaries slip past each other.
• The plates may be stuck for years, then
suddenly break free and move several
inches or even feet.
Transform Boundary – San Andreas Fault
www.geology.com
Review
• Name the 3 main layers of the Earth.
– Crust, Mantle, Core
• What is a tectonic plate?
– Piece of the lithosphere that moves around.
• What was Pangea?
– A supercontinent from about 245 million years ago.
• Name the three different types of plate
boundaries and one location on Earth for each
one
– Convergent = Eurasian and Indian Plates
– Divergent = Arabian and African Plates
– Transform = San Andres Fault