Canada’s Geologic History
Introduction
Cross-section of Earth
The Earth’s
surface is a thin
layer of moving
plates, floating on
more fluid layers
of molten rock
surrounding the
Earth’s core.
• About 300 million years
ago (MYA), the plates
were one large plate or
supercontinent called
Pangaea.
• Over millions of years,
the plates slowly moved
apart to form the
present continents.
• This is why many of the
continents such as
Africa and South
America look as if they
could fit easily together
like a jigsaw puzzle.
Continental Drift and Alfred Wegener
• In 1915, Alfred Wegener suggested
the idea of Continental Drift to explain
the movement and relative position of
the Earth’s continents.
• Wegener based his theory on four
observations:
- Jigsaw puzzle outline of continents
- Similar fossils of the same age on
different continents
- Similar rocks in mountain ranges on
different continents
- Remnants of an ice age in present
warmer regions of Earth
Plate Tectonics
Continental Drift is caused by the
movement of the Earth’s plates. This
theory is called Plate Tectonics.
Plate Tectonics is a relatively new
idea…developed between 1960 and
1970.
The plates move constantly, in
different directions at a very, very
slow rate (about 2-10 cm/yr).
Plate movement is caused by many
factors including currents in the
Mantle and the separation of the
ocean floors.
Continental Drift - Proof
• The Appalachian
Mountains in North
America bear a striking
resemblance to the
Caledonian Mountains in
Europe (e.g., similar age of
rocks)
• Although thousands of
kilometres apart, the two
mountain ranges must
have been formed by the
same geologic forces
More Evidence for Continental Drift
• Fossil records indicate that
Africa, India, Australia and
South America were all
covered by ice sheets
approximately 250 MYA.
• How could ice form in areas
with such warm climates?
• With Wegener’s theory,
these land masses were, at
one point in geological
history, located closer to
the South Pole…and its
extremely cold climate
Key Principles
• The Earth’s surface is made up of
about 20 different plates floating on a
liquid layer of molten rock called the
Mantle.
• The plates are constantly moving at a
slow rate.
• One of the causes of plate movement
is CONVECTION CURRENTS in the
Mantle. At the core, the Mantle is hot,
while at the crust, it is cooler. These
heat differences create a current (i.e.,
hot rises, cools falls).
• These currents apply force to the
plates causing them to shift and move.
• These plates are constantly
interacting with each other In
processes called FOLDING or
FAULTING.
• These interactions are
responsible for geologic
occurrences which shape the
world’s geography. For
example, mountain ranges
such as the Rockies in British
Columbia were formed by
tectonic forces. As well,
Canada’s fossil fuel resources
were formed by the movement
of plates. Gas, oil and coal
were formed when Canada
was located in a warmer
climate.
Types of Plate Boundaries
• TRANSFORM BOUNDARIES – These occur when two plates
grind past each other in a side to side motion (e.g., San
Andreas fault in California)
• DIVERGENT BOUNDARIES – Two plates moving apart from
each other form this type of boundary. The cooling of the
molten rock when it reaches the surface causes new crust to be
formed constantly (e.g., Mid-Atlantic Ridge)
• CONVERGENT BOUNDARIES – Two plates moving towards
each other create this fault. Typically one plate is forced above
the other, contributing to the formation of mountain ranges
(e.g., Andes mountains in South America)
Plate Boundaries
Earthquakes and Volcanoes
• Why are most earthquakes and volcanoes located near plate
boundaries?
• As different plates collide and interact, they cause a number of
phenomena. Two moving plates, typically on a Transform Fault,
could potentially snag on each other and build up energy. If this
energy is released suddenly, it causes an earthquake.
• If two colliding plates build up friction, that heat can break
down the crust in certain areas causing vents to form from the
outer core of magma to the surface. These take the form of
volcanoes.
Connections?
Is there any link between the fault lines between
tectonic plates and the sites of major earthquakes and
volcanoes. The region encircling the Pacific Ocean is
called the Ring of Fire.
TASK - ACTIVITY
• You may choose between the following two
exercises on Plate Tectonics theory.
1) Using any materials in the classroom
create a model or diagram which
demonstrates the movement of plates
on the Earth’s surface. Be sure to
include both the surface plates AND
the Earth’s mantle and core. Consult
page 92 in your textbook for additional
information.
2) Using any materials in the classroom
create a model or diagram which
explains how volcanoes or
earthquakes are caused by plate
tectonics. Consult page 95 in your
textbook for additional information.