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Title: Plate%20Tectonics:%20Earth's%20Plates%20and%20Continental%20Drift


1
Plate TectonicsEarth's Plates and Continental
Drift
2
  • Some questions we will answer today
  • How is the earth always changing?
  • What forces inside the earth create and change
    landforms on the surface?
  • What is the theory of plate tectonics and how
    does it work?
  • What two theories help make up the theory of
    plate tectonics?
  • What is continental drift and sea floor
    spreading?
  • What happens when the plates crash together, pull
    apart, and slide against each other?

3
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 the landforms, or natural
    features, found on the surface of the earth.

4
  • Before we start to look at the forces that
    contribute to landforms,lets look at the
    different layers of the earth that play a vital
    role in the formation of our continents,
    mountains, volcanoes, etc.

5
Crust
Mantle
Outer Core
Inner Core
crust - the rigid, rocky outer surface of the
Earth, composed mostly of basalt and granite. The
crust is thinner under the oceans. mantle - a
rocky layer located under the crust - it is
composed of silicon, oxygen, magnesium, iron,
aluminum, and calcium. Convection (heat) currents
carry heat from the hot inner mantle to the
cooler outer mantle. outer core - the molten
iron-nickel layer that surrounds the inner core.
inner core - the solid iron-nickel center of the
Earth that is very hot and under great pressure.
6
DID YOU KNOW?
7
Land and Water
  • Photographs of the earth taken from space show
    clearly that it is a truly a watery planet.
  • More than 70 percent of the earths surface is
    covered by water, mainly the salt water of oceans
    and seas.

8
Land
  • The large landmasses in the oceans are called
    continents.
  • List the continents in your notes.
  • Landforms are commonly classified according to
    differences in relief. The relief is the
    difference in elevation between the highest and
    lowest points. Another important characteristic
    is whether they rise gradually or steeply.
  • The major types of landforms are mountains,
    hills, plateaus, and plains.

9
  • Together, lets look at your Land and Water
    Features handout.
  • Please join me in filling out the correct
    answers. Use a map pencil to color the different
    types of land and water features.

10
  • Most people know that Earth is moving around the
    Sun and that it is constantly spinning.
  • But did YOU know that the continents and oceans
    are moving across the surface of the planet?
  • Volcanoes and earthquakes as well as mountain
    ranges and islands all are results of this
    movement.
  • Why is this?

11
  • Plate Tectonics

12
  • Most of these changes in the earths surface
    takes place so slowly that they are not
    immediately noticeable to the human eye.
  • 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.

13
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. 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!) Currently Earths surface layers are
divided into nine very large plates and several
smaller ones.
14
  • 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. The plates vary in size
    and thickness.

15
  • The North American Plate stretches from the
    mid-Atlantic Ocean to the northern top of Japan.
    The Cocos Plate covers a small area in the
    Pacific Ocean just west of Central America.
  • These plates are not anchored in place but slide
    over a hot and bendable layer of the mantle.

16
  • How is the earth always changing?
  • What is the theory of plate tectonics and how
    does it work?

17
  • 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.

18
  • Less than 100 years ago, many scientists thought
    the continents always had been the same shape and
    in the same place.
  • A few scientists noted that the eastern coastline
    of South America and the western coastline of
    Africa looked as if they could fit together.
  • Some also noted that, with a little imagination,
    all the continents could be joined together like
    giant puzzle pieces to create one large continent
    surrounded by one huge ocean.
  • In your study groups for today, take your
    continent cut outs and shape them into one large
    land mass.

19
So, if my contintents fit together, why does the
earth look like it does today?
20
Continental Drift Theory
  • When the tectonic plates under the continents and
    oceans move, they carry the continents and oceans
    with them.
  • In the early 1900s a German explorer and
    scientist proposed the continental drift theory.
    He proposed that there was once a ingle
    supercontinent called Pangaea.

21
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22
  • Wegners theory was that about 180 million years
    ago, Pangaea began to break up into separate
    continents. To back this theory up, he perserved
    remains and evidence from ancient animals and
    plants from South America, Africa, India, and
    Australia that were almost identical.

23
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. The youngest rocks were
    those nearest the underwater ridge system which
    is a series of mountains that extend around the
    world, stretching more than 64 thousand
    kilometers (40 thousand miles).

24
  • The theory of seafloor spreading suggests that
    molten rock (think of a melted chocolate bar that
    has been left in your pocket for too long)...
    This hot substance (lava) from the mantle rises
    under the underwater ridge and breaks through a
    split at the top of the ridge (the crust...
    Remember, the plate). The split is called a rift
    valley. The rock then spreads out in both
    directions from the ridge as if it were on two
    huge conveyor belts. As the seafloor moves away
    from the ridge, it carries older rocks away.
    Seafloor spreading, along with the continental
    drift theory, became part of the theory of plate
    tectonics.

25
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.
26
  • What two theories help make up the theory of
    plate tectonics?
  • What is continental drift and sea floor
    spreading?

27
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?

28
  • What is their answer?

29
Plate Tectonics
  • But this doesnt actually tell me how the
    mountains or volcanoes were formed or how
    earthquakes happen, does it?

30
YES!
  • As mentioned earlier, those tectonic plates are
    always moving. They are always moving
  • 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 you
and I are standing on.
31
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.
32
The Crash!
  • What happens when plates crash into each other
    depends on the types of plates involved.
  • Because continental crust is lighter than oceanic
    crust, continental plates float higher.
  • Therefore, when an oceanic plate meets a
    continetnal plate, it slides under the lighter
    plate and down into the mantle. The slab of
    oceanic rock melts when the endges get to a depth
    which is hot enough. A temperature hot enough to
    melt si about a thousand degrees!) This process
    is called subduction. Molten material produced
    in a subduction zone can rise to the earths
    surface and cause volcanic building, mountains,
    and islands.

33
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34
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.

35
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.

36
Converging...They Crash! And theyre both
Continental Plates
  • When both are continental plates, the plates push
    against each other, creating mountain ranges.

37
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!

38
They meet and slide past each other!
  • Sometimes, instead of pulling away from each
    other or colliding with eac hother, plates slip
    or grind past each other along faults. This
    process is known as faulting.

39
  • These areas are likely to have a rift valley,
    earthquake, and volcanic action.

For example Here, 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 wit hearthquakes.
40
  • 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?

41
  • All graphics were taken from Google Images,
    enchanted learning, boom zone, and other
    educational sites.
  • All written information was taken from Prentice
    Hall, World Geography, PBS.org, and other
    educational websites.
  • A good website for a deeper understanding is
    www.observe.arc.nasa.gov/
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