2. Wegener
1880-1930
earthobservatory.nasa.gov
Alfred Wegener first proposed the
theory of continental drift.

3.  Continental drift was Wegener’s theory
that all continents had once been joined
together in a single landmass and have
drifted apart since.
 Wegener named this supercontinent
Pangaea.
 Wegener’s theory was rejected by
scientists because he could not explain
what force pushes or pulls continents.
Continental drift video clip

5. Fit of Continents
Across the Atlantic
Mountain ranges in
South America line
up exactly with
those in Africa!

6. http://evolution.berkeley.edu/evolibrary/images/history/fossils3.gif
Notice how fossils lined up across continents!

7. Amazing Facts: Did you know...
...that India was once in the Southern Hemisphere
connected to Antarctica?
...that North America was once surrounded by warm,
tropical seas?
...that Africa was once covered by glaciers, which were
kilometers in thickness?
...that the Sahara desert was once a tropical rain forest?

8. An example of the proof for changing climate:
At one time,
the area that
is New
Mexico (and
the rest of
the USA was
below the
equator!
As North America has drifted to different latitudes,
changing climates were experienced. This shows the
changes in the state of New Mexico.

9. He could not find the force that was
causing the continents to drift.
Because of this, he could not convince
anyone that continents could move.
He died in Greenland on an expedition.
At the time of his death, no one believed
his hypothesis!
Technology developed during the 1940’s
changed all that!

10. Discovery of Sea-Floor Spreading
Sea floor spreading video clip

11. Sea-Floor
Spreading
m.y.
means
million
years ago
Notice this
compass. It
is important
for the next
slide

13. http://platetectonics.pwnet.org/img/blocks.gif
As the sea floor spreads, the lava cools according to the
magnetic poles at the time. The rocks on the ocean
floor have proved that the earth’s magnetic field
sometimes reverses. The inner core flips and so the
north pole moves to the southern hemisphere! The
earth itself does not flip.

14. What causes sea floor spreading?
Convection currents!

15. Click here for a hyperlink to an animation of convection
Be sure to click the play button!

16. Animation of sea floor spreading
Can you explain this diagram!?

17. The place where two plates move
apart or diverge is called a divergent
boundary.

18. This is a model of sea floor spreading at a divergent
boundary called a mid ocean ridge.

19. : www.ocean.udel.edu
Did you know that the Earth’s longest mountain range is
underwater and is called the mid-ocean ridge?
The Mid-Ocean Ridge system, shown above snaking its way
between the continents, is more than 56,000 kilometers (35,000 mi)
long. It circles the earth like the stitching on a baseball!

20. Continental crust diverging from continental

21. A convergent boundary is where two plates
come together, or converge. The result of the
plates hitting together is called a collision.

22. A transform boundary is a place where
two plates slip past each other, moving in
opposite directions.

23. San Andreas Fault in California

24. en ta l
on tin
oc
ru st t
t al c Continen
ta l c ru s t to
n en o c e a n ic
nti
Co
Oceanic crust to oceanic

25. Continental crust to continental crust
collision Before collision
India-Asia (Himalayas) After collision
from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270

29. Because one plate gets pushed under
another, it is called subduction. This
is where volcanoes form!
Oceanic crust
Oceanic crust colliding
colliding with
with continental crust
oceanic crust
all from: http://www.geo.lsa.umich.edu/~crlb/COURSES/270

32. The process by
which the ocean
floor sinks
beneath a deep-
ocean trench
and back into
the mantle is
called

33. Here is an great link for seeing where each type of
boundary is located.
Click here for a great hyperlink! Make sure you
click on each type of boundary in the key!
Plate tectonics video clip

34. Worldwide Earthquake patterns help us
know where the edges of plates are located

35. The Earth’s Plates

36. Here you see
the two slides
together.
What do you
see?

37. http://www.livescience.com/images/pangea_animation_03.gif