Download Overhead: Continental Drift / Plate Tectonics

Physical Geography
Continental Drift / Plate Tectonics
Geologic History
•  The surface of the earth is a thin layer of moving plates that float on the
mantle.
•  Each earthquake is an indication of the movement of the earth’s upper
layer called the crust.
•  Seismologists (scientists who study earthquakes) have discovered that
earthquakes occur more frequently in specific areas.
•  Earthquakes and volcanoes frequently occur where the edges of the
earth’s plates are spreading, colliding, or sliding from one another.
Types of Plate Behaviour
Spreading / Divergent
Colliding / Convergent
Sliding / Transform
The Earth’s Interior
A.  Crust
B.  Upper Mantle
C.  Asthenosphere
D.  Lower Mantle
E.  Outer Core
F.  Inner Core
Moho Discontinuity – The dividing line
between the asthenosphere and the earth’s
crust.
Gutenberg Discontinuity – The dividing
line between the solid mantle and the liquid
core of the earth.
Alfred Wegener’s Theory of
Continental Drift
①  He saw the jigsaw fit between South America and Africa.
②  He found fossils of the same plants and animals on different
continents.
③  There are mountains similar in age and structure on both sides of the
Atlantic Ocean ! the Appalachian Mountains in North America were
similar to the Caledonian Mountains in Europe.
④  Glaciers once covered southern Africa, India, Australia and South
America.
Why did most scientists disagree with Wegener?
"  Wegener could not explain what mechanism was powerful enough
to move huge continents.
Alfred Wegener’s Theory of
Continental Drift
Plate Tectonics
•  In the 1960’s the idea of continental drift was revived by John Tuzo
Wilson (Canadian geophysicist and geologist).
•  He conducted a detailed analysis of glaciers, mountains and sea beds.
"  He expanded on Wegener’s ideas by establishing the concept that
the continents moved on plates
•  About 300 million years ago all the earth’s land masses were joined
together into one supercontinent called Pangaea
•  About 200 million years ago Pangaea began to break up, with each
tectonic plate moving in a different direction.
Plate Behaviour
Pangaea
Given the currently
estimated drift rates and
directions of the plates, we
can trace their movements
back into the past. About
200 million years ago, they
would have been at the
approximate positions
shown in (a). The
continents’ current
positions are shown in (d)
Theory of Plate Tectonics
•  The earth’s crust is made up of about 20 plates.
•  These plates are moving over a layer of molten rock known as the
mantle.
•  It is believed that the unequal distribution of heat within the earth
causes convection currents to move the plates.
Mount Kilauea, Hawaii / Kobe, Japan
[A] An active volcano on Mount Kilauea in Hawaii. Kilauea seems to be a
virtually ongoing eruption.
[B] The aftermath of the earthquake that claimed more than 5000 lives and
caused billions of dollars' worth of damage in Kobe, Japan in January 1995.
San Andreas Fault
The San Andreas and
associated faults in
California result from the
North American and
Pacific plates sliding past
one another.
(a) A small part of the
fault line separating the
two plates. (b) A satellite
photo of the San
Francisco Bay area,
showing the location of
two fault lines. (c) A
larger-scale view of the
fault system.
Evidence of Plate Tectonics
①  Coastline Fit – Continents fit together like a jigsaw puzzle.
②  Geologic Fit – similar mountains in North America and Europe.
③  Glacial Evidence – Evidence that glacier existed on Africa, Australia,
India and South America.
④  Fossil Correlation – Similar fossils of plants and animals found on
adjacent continents.
Evidence of Plate Tectonics (continued)
⑤  Paleomagnetism – As volcanic rock cools magnetic elements align
themselves with the earth’s magnetic field.
⑥  Mid-oceanic Ridge – Rocks are younger closer to the ridge and older as
you move further away from it.
⑦  Satellite Measurements – Satellites have detected that the plates are
moving 1-2 cm per year.
Major Earthquakes and Volcanoes
Red dots represent active sites where major volcanoes or earthquakes
have occurred in the twentieth century. The sites outline vast "plates" that
drift around on the surface of our planet.
Earthquakes in Canada
Significant Earthquakes in Canada