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Continental Drift and Plate Tectonics

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Title: Continental Drift and Plate Tectonics Author: Steven Dutch Last modified by: User Created Date: 1/18/2001 12:21:04 AM Document presentation format – PowerPoint PPT presentation

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Title: Continental Drift and Plate Tectonics


1
Continental Drift and Plate Tectonics
2
Wegener 1880-1930
earthobservatory.nasa.gov
  • Alfred Wegener first proposed the theory of
    continental drift.

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

Continental drift video clip
4
Wegener searched and found three main pieces of
evidence.
Geologic - evidence in the layers of rocks
across continents
Fossil - evidence in the places certain fossils
are found
Climate - evidence in the changing climates
during the past
5
Fit of Continents Across the Atlantic Mountain
ranges in South America line up exactly with
those in Africa!
Geologic evidence
6
Fossil evidence
http//evolution.berkeley.edu/evolibrary/images/hi
story/fossils3.gif
Notice how fossils lined up across continents!
7
Climate change
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 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
Wegener's problem
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 1940s 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
12
Amazing proof of that the inner core flips!
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
earths magnetic field sometimes reverses. The
inner core flips and so the north pole moves to
the southern hemisphere! The earthh itself does
not flip.
13
What causes sea floor spreading? Convection
currents!
14
Can you explain this diagram?
Click here for a hyperlink to an animation of
convection
Be sure to click the play button!
15
Animation of sea floor spreading
Can you explain this diagram!?
16
  • The place where two plates move apart or diverge
    is called a divergent boundary.

17
This is a model of sea floor spreading at a
divergent boundary called a mid ocean ridge.
18
www.ocean.udel.edu
Did you know that the Earths 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!
19
Plates can also move together!
  • A convergent boundary is where two plates come
    together, or converge. The result of the plates
    hitting together is called a collision.

20
Plates can also slide past each other.
  • A transform boundary is a place where two plates
    slip past each other, moving in opposite
    directions.

21
There are three conbinations of how earth's
crust can come together.
Continental crust to continental
Continental crust to oceanic
Oceanic crust to oceanic
22
Continental crust to continental crust collision
Before collision
India-Asia (Himalayas)
After collision
from http//www.geo.lsa.umich.edu/crlb/COURSES/2
70
23
This is how the Himalaya Mountains formed
Also the way the Appalachian Mountains formed!
24
Because one plate gets pushed under another, it
is called subduction. This is where volcanoes
form!
Oceanic crust colliding with oceanic crust
Oceanic crust colliding with continental crust
all from http//www.geo.lsa.umich.edu/crlb/COURS
ES/270
25
The process by which the ocean floor sinks
beneath a deep-ocean trench and back into the
mantle is called
subduction
26
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
27
Worldwide Earthquake patterns help us know where
the edges of plates are located
28
The Earths Plates
29
Here you see the two slides together. What do
you see?
30
http//www.livescience.com/images/pangea_animation
_03.gif
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