Download Movement of the Earth Theory of Plate Tectonics

Movement of the Earth
Theory of Plate Tectonics
(Part 1)
Continental Drift
Hypothesis
• In 1912 Alfred Wegener suggested that all the
continents were once connected as one large
landmass now called Pangaea.
• Pangaea means “all land”.
• The landmass broke apart about 200 million
years ago and the continents slowly drifted to
their present positions.
Seafloor Spreading
-explains the motion of the
continents
• Hot dense material below the Earth’s crust rises upward
to the surface at the mid-ocean ridges.
• It then flows sideways, carrying the seafloor away from
the ridge.
• As the new seafloor spreads apart, magma moves up and
flows from the cracks, cools, and forms new seafloor.
• Youngest rocks are located at the mid-ocean ridges and
become increasingly older the further out you go.
Plate Tectonics
• In the 1960’s scientists developed a new
theory that combined continental drift and
seafloor spreading.
• It is called The Theory of Plate Tectonics.
Plate Tectonics
• The Earth’s crust and upper mantle are broken
into sections.
• The sections, called plates, move on a plastic-like
layer of the mantle.
– Geologists use the term plastic to describe the
consistency of rock that flows but is not a liquid like
Silly Putty, modeling clay, or toothpaste.
Plate Tectonics
• The plates and upper mantle form the
lithosphere.
– The lithosphere is about 100km thick and generally is
less dense than the material underneath.
• The plastic-like layer is called the asthenosphere.
– The rigid plates of the lithosphere float and move
around on the asthenosphere.
Plate Boundaries
• When plates move, they can interact in several
ways.
– They can collide, pull apart, or slide alongside each
other.
• When plates interact, the result of their
movement can be seen at the plate boundaries.
Divergent
Boundaries
• Plates moving apart at the mid-ocean
ridges are examples of divergent plate
boundaries.
– In the Atlantic Ocean, the North
American Plate is moving away from the
Eurasian and the African Plates.
– The Great Rift Valley in eastern Africa
may become a divergent boundary. The
continental plate is being pulled apart.
Convergent Boundaries
• As new crust is added in one place, it
disappears below the surface at another.
Convergent
Boundaries
• When Ocean and Land Plates
Meet:
– The denser oceanic plates sink under less dense
continental (land) plates.
– The area where the ocean plate moves down is called
a subduction zone.
– This type of convergent boundary forms a deep sea
trench.
Convergent Boundaries
• When Ocean and Land Plates
Meet (continued):
– Newly formed hot magma is forced
upward along the subduction zones
and forms volcanic mountains.
– The Andes Mountain Range in
South America contains many
volcanoes that were formed at the
convergent boundary of the Nazca
and South American Plates.
Convergent Boundaries
• When Two Oceanic Plates Collide:
– The older, denser plate will
subduct and sink down into the
mantle.
– The Mariana Islands in the
Western Pacific are a chain of
volcanic islands formed from two
oceanic plates colliding.
Convergent
Boundaries
• When Two Continental (Land)
Plates Collide:
– There is usually no subduction
because both of these plates are less
dense than the material of the
asthenosphere.
– Plates will crumple up to form
mountain ranges.
– Earthquakes are common here, but
not volcanoes.
– The Himalayas in Asia are forming
where the Indo-Australian Plate
collides with the Eurasian Plate.
Eurasian
Plate
Indo-Australian
Plate
Transform Boundary
• When one plate slips past another suddenly,
earthquakes occur.
– The Pacific Plate is sliding past the North American
Plate forming the famous San Andreas Fault in
California.
Causes of
Plate Tectonics
• Convection inside the Earth
– Cycle of heating, rising, cooling
and sinking is called a
convection current.
– This process occurring inside the
mantle of the Earth is the
driving force behind plate
tectonics.
Convection
currents occur
inside the
mantle. They
are the driving
force behind
plate tectonics.
Features Caused by Plate
Tectonics
• The interaction of plates produces
forces that build mountains,
create ocean basins, and cause
volcanoes.
• When rocks in the Earth’s crust
break and move, the energy is
released as seismic waves.
• We feel this release as an
earthquake.
Features Caused by
Plate Tectonics
• Mid-Ocean Ridges, Faults and Rift Valleys –
formed at divergent boundaries where plates are
pulled apart
• Mountains and Volcanoes – formed at
convergent boundaries where plates collide
• Strike-Slip Faults- cause of earthquakes and are
found at transform boundaries where plates
grind past each other
Testing for Plate
Tectonics
• Using lasers and satellites, scientists can measure
movements as little as 1 cm per year.
• Scientists have observed that the plates move at
rates from about 1cm to 12cm per year.
– Hawaii is moving toward Japan at a rate of about 8.3
cm per year.
– Europe and North America are moving away from
each other at the rate of about 3 cm per year.
Part 1 Assessment
Using a separate sheet of paper, answer
the following questions.
1) What happens to plates at a transform boundary?
2) What occurs at plate boundaries that are
associated with seafloor spreading?
3) Describe the types of plate boundaries where
volcanic eruptions can occur.
4) How are convection currents related to plate
tectonics?
5) Using a flow map, describe the three theories
that were discussed at the beginning of the
PowerPoint.
Part 1 Assessment
ANSWERS
1)
What happens to plates at a transform boundary?
One plate slips past another suddenly,
resulting in an earthquake.
2)
What occurs at plate boundaries that are associated with
seafloor spreading?
Oceanic crust is very dense
compared to land crust, so it
sinks beneath land crust and
pulls away from other ocean
plates. When this happens, a
void is left at the plate boundary.
Magma fills the void where it
cools to create new oceanic
crust. It is a continual process.
Part 1 Assessment
ANSWERS (continued)
3)
Describe the types of plate boundaries where volcanic
eruptions can occur.
• Diverging boundaries (plates pulling
apart) either on the ocean floor or on
land
• Converging boundaries where an ocean
plate collides with a land plate or where
two ocean plates collide.
Part 1 Assessment
ANSWERS (continued)
4)
How are convection currents
related to plate tectonics?
Magma can heat, rise, cool,
and sink just like water can
when boiling or air can
creating wind. Magma is
heated below Earth’s
surface. This heated, less
dense magma rises towards
Earth’s crust where it cools
and become more dense. It
sinks back down towards
Earth’s surface where it’s
heated again, starting the
cycle over.
Part 1 Assessment
ANSWERS (continued)
5)
Using a flow map, describe the three theories that were
discussed at the beginning of the PowerPoint.
CONTINENTAL
DRIFT - In 1912
Alfred Wegener
suggested that all
the continents were
once connected as
one large landmass
now called Pangaea.
The land mass broke
apart about 200
million years ago
and the continents
slowly drifted to
their present
positions.
SEAFLOOR
SPREADING –
Refer to question
#2 for
description
THE THEORY of
PLATE TECTONICS In the 1960’s
scientists developed
a new theory that
combined
continental drift and
seafloor spreading.