Some questions we will answer today:

1
0
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?
• 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?

0
3
The Earths Layers
0

• 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.

4

• Lets look at the different layers of the earth
  that play a vital role in the formation of our
  continents, mountains, volcanoes, etc.

0
5
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.
0
6
Remember the crust and the upper part of
the mantle make up the lithospherethe rest of
the mantle is the asthenosphereouter 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.
0
7
0

• 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?

8
0

• Plate Tectonics

9
0

• 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.

10
Plate Tectonic Theory
0
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.
11

• 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.

0
12
0

• 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.

13
0

• 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.

14
0

• 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.

15
0

• 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.

16
Continental Drift Theory
0

• 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.

17
0
18

• 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. Rock
  sequences and glaciation also was evidence.

0
19
Seafloor Spreading
0

• 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.

20
0

• The theory of seafloor spreading suggests that
  molten rock, the hot substance (lava) from the
  mantle rises under the underwater ridge and
  breaks through a split at the top of the ridge
  (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.

21

• Evidence to support sea-floor spreading is
  magnetic mapping. When the rock is magma/lava it
  allows the atoms of the metals to align with the
  magnetic poles of the earth. These magnetized
  metals cool and form rocks and then can be mapped
  using magnetic equipment. This along with
  radiometric dating proves sea-floor spreading.

0
22

0

• Seafloor spreading, along with the continental
  drift theory, became part of the theory of plate
  tectonics.

23
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.
0
24
0

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

25
0

• As mentioned earlier, tectonic plates are always
  moving. They are always moving
• pulling away from each other (Divergent plate
  boundary)
• crashing head-on (Convergent plate boundary)
• or sliding past each other. (Transform plate
  boundary)

26
Theyre Pulling Apart!
0

• 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.
27
The Crash!
0

• 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.
• 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.
  This process is called subduction. Molten
  material produced in a subduction zone can rise
  to the earths surface and cause mountains, and
  islands.

28
0
29
When they Crash
0

• 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.

30
0
31
Converging...They Crash! And theyre both
Continental Plates
0

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

32
A Crash and are both continental plates!
0

• 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!

33
They meet and slide past each other!Transform
plate boundary
0

• 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.

34

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

0
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.
35
What evidence supports continental drift.

• similar rock sequences.
• Similar glaciation patterns.
• Similar fossils of plant and animals.
• All of the above.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32
36
What evidence supports sea floor spreading.

1. Magnetic mapping.
2. Igneous intrusion.
3. Similar glaciation patterns.
4. All of the above.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32
37
When two plates slide past each other what type
of plate boundary is it?.

1. Convergent .
2. Divergent.
3. Transform.
4. Subduction.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32
38
When two plates go away from each other what type
of plate boundary is it?.

1. Convergent .
2. Divergent.
3. Transform.
4. Subduction.

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
21 22 23 24 25 26 27 28 29 30 31 32