Plate Tectonics: Earth's Plates and Continental Drift

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Plate TectonicsEarth's Plates and Continental
Drift
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• Questions we will answer
• How is the earth always changing?
• What forces inside the earth create and change
  landforms on the surface?
• What happens when the plates crash together, pull
  apart, and slide against each other?

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Review - The Earths Layers

• The Earth is made of many different and distinct
  layers.
• The deeper layers are composed of heavier
  materials they are hotter, denser and under much
  greater pressure than the outer layers.
• Natural forces interact with and affect the
  earths crust, creating landforms, or natural
  features, found on the surface of the earth.

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• Layers of the Earth

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Land and Water

• More than 70 percent of the earths surface is
  covered by water, mainly the salt water of oceans
  and seas.

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Land

• The large landmasses in the oceans are called
  continents.
• List the continents in your notes.

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Types of Landforms

• Landforms are commonly classified according to
  differences in relief.
• The relief is the difference in elevation between
  the highest and lowest points.
• The major types of landforms are mountains,
  hills, plateaus, and plains.

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DID YOU KNOW?

• that the continents and oceans are moving across
  the surface of the planet?
• that volcanoes and earthquakes, as well as
  mountain ranges and islands, all are results of
  this movement.
• Why is this?

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• Plate Tectonics

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• According to the theory of plate tectonics, the
  earths outer shell is not one solid piece of
  rock. Instead the earths crust is broken into a
  number of moving plates.

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• The idea that the earths landmasses have broken
  apart, rejoined, and moved to other parts of the
  globe forms part of the plate tectonic theory.
• Most of these changes in the earths surface
  takes place so slowly that they are not
  immediately noticeable to the human eye.

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Plate Tectonic Theory

• About forty years ago, scientists exploring the
  seafloor found that it is full of tall mountains
  and deep trenches.
• A single seafloor mountain chain circles Earth
  and contains some of Earths tallest mountains.

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Plate Tectonic Theory

• Along this mountain chain is a deep crack in the
  top layers of earth.
• Here the seafloor is pulling apart and the two
  parts are moving in opposite directions, carrying
  along the continents and oceans that rest on top
  of them.
• These pieces of Earths top layer are called
  tectonic plates.
• They are moving very slowly, but constantly.
  (Most plates are moving about as fast as your
  fingernails are growing -- not very fast!)
• These plates but slide over a hot and bendable
  layer of the mantle.
• Currently Earths surface layers are divided into
  nine very large plates and several smaller ones.

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• To really understand how the earth became to look
  as it does today, and the theory of plate
  tectonics, you also need to become familiar with
  two other ideas
• Continental Drift
• and
• Seafloor Spreading.

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• Continental Drift
• In a group, cut out the continents and shape them
  into one large land mass.

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So, if my contintents fit together, why does the
earth look like it does today?
http//www.wwnorton.com/college/geo/egeo/flash/2_1
.swf
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Seafloor Spreading

• The other theory theory supporting plate
  tectonics emerged from the study of the ocean
  floor.
• Scientists were suprised to find that rocks taken
  from the ocean floor were much younger than those
  found on the continents.
• http//education.sdsc.edu/optiputer/flash/seafloor
  spread.htm

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Plate motions also can be looked at into the
future, and we can have a stab at what the
geography of the planet will be like. Perhaps in
250 million years time there will be a new
supercontinent.
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Turn to your neighbor and discuss.

• What two theories help make up the theory of
  plate tectonics?

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So....

• When a geologist or a geographer looks at a piece
  of land they often ask, What forces shaped the
  mountains, plains, and other landforms that are
  here?

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Plate Tectonics

• What is their answer?

But this doesnt actually tell me how the
mountains or volcanoes were formed, or how
earthquakes happen, does it?
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YES!

• As mentioned earlier, those tectonic plates are
  always moving by
• pulling away from each other
• crashing head-on
• or sliding past each other.

Depending on which way these plates are moving
will decide what is happening on the earth where
you and I are standing.
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Theyre Pulling Apart!

• When plates pull away from one another they form
  a diverging plate boundary, or spreading zone.

Thingvellir, the spreading zone in Iceland
between the North American (left side) and
Eurasian (right side) tectonic plates. January
2003.
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When they Crash!

• When two plates of the same type meet, the result
  is a process called converging.
• Depending on what type of plates these are,
  depends on what occurs.

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Converging... They crash! And theyre both ocean
plates!

• When both are oceanic plates, one slides under
  the other. Often an island group forms at this
  boundary.

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Converging...They Crash! And theyre both
Continental Plates

• When both are continental plates, the plates push
  against each other, creating mountain ranges.

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They Crash and are both continental plates!

• Earths highest mountain range, the Himalayas,
  was formed millions of years ago when the
  Indo-Australian Plate crashed into the Eurasian
  Plate. Even today, the Indo-Australian Plate
  continues to push against the Eurasian Plate at a
  rate of about 5 cm a year!

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They meet and slide past each other!

• Sometimes, instead of pulling away from each
  other or colliding with each other, plates slip
  or grind past each other along faults.
• This process is known as faulting.

• These areas are likely to have a rift valley,
  earthquake, and volcanic action.

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They meet and slide past each other!

• Example The San Andreas Fault lies on the
  boundary between two tectonic plates, the north
  American Plate and the Pacific Plate.
• The two plates are sliding past each other at a
  rate of 5 to 6 centimeters each year.
• This fault frequently plagues California with
  earthquakes.