Download Plate Tectonics - Mr. Brown`s Science Town

Plate Tectonics
The Dynamic Interior of the Earth
Review of Earth’s Interior:
1. Name, in order going from the center of the
Earth to where we live, the four major layers of
the Earth.
2. What composes the lithosphere?
3. How do the two layers closest to the center of
the Earth differ in their composition?
4. Describe how scientists determine the
composition of the different layers of the Earth.
If you look at a map of the world, do you notice anything
interesting about the shapes of the continents?
Plate Tectonics
• https://www.youtube.com/watch?v=
_5q8hzF9VVE
• The Earth’s crust is divided into 12
major plates which are moved in
various directions.
• This plate motion causes them to
collide, pull apart, or scrape against
each other.
Plate Tectonics
• The plate
interactions cause
the Earth
structures
(mountains,
trenches, etc.).
• Tectonic:
deformation of
the crust because
of a plate
interaction.
What are tectonic plates made
of?
• Plates are made of
rigid lithosphere.
• Remember - The
lithosphere is
made up of the
crust and the
upper part of the
mantle.
Theory of Continental Drift
• Proposed by Alfred
Wegener in early
1900’s.
• He hypothesized
that the continents
were once joined
together in a single
large land mass he
called Pangaea
Theory of Continental Drift
• Pangaea split apart
and the continents
moved gradually to
their present
positions
• Process is known as
Continental Drift
Pangaea, about 200 million years ago, before it began breaking up.
Wegener named the southern portion of Pangaea Gondwana, and
the northern portion Laurasia.
The continents about 70 million years ago. Notice that the breakup
of Pangaea formed the Atlantic Ocean. India’s eventual collision
with Eurasia would form the Himalayan Mountains.
Learning Check
• What layer of the Earth composes the
tectonic plates?
• How many “major” plates make up the
Earth?
• Who developed the theory of plate
tectonics?
• Describe Pangaea.
Evidence of Continental Drift
1. Continents fit
together like a
puzzle.
• Ex. - The Atlantic
coastlines of
Africa and South
America.
More Evidence…
2. Fossils of
several plants
and animals of
the same species
found on
different
continents.
Ex. Mesosaurus
Some More Evidence
3. Rock and Mountain
Correlation.
Identical rocks and
mountain structures
have been found on
either side of the
ocean.
• The order of rock layers
in South America,
Africa, India, Antarctica,
and Australia show
remarkable similarities.
Last Piece of Evidence
4. Ancient
climate information.
• Coal has been found in cold regions and
glacial evidence has been found in warm
climates.
Another Learning Check…
1. Explain at least 3 pieces of evidence used
to support Wegener’s theory of
continental drift.
Was Wegener Correct?
• Everyone agreed that
Wegener’s evidence
was compelling. But
wouldn’t we feel the
movement?
• Also, wouldn’t there be
evidence to show that
the continents were
still moving today?
• Wegener was a
meteorologist and his
theory was not well
accepted. (He died on
an expedition in
Greenland collecting
ice samples)
Holes in Wegener’s Theory…
• One reason
scientists had a
hard time with
Wegener’s theory
is that there was
no mechanism for
the continents
motion.
Sea Floor Spreading
• Henry Hess
• 1960’s
• Using new
technology, radar,
he discovered that
the seafloor has
both trenches and
mid-ocean ridges.
• Proposed the seafloor spreading
theory.
Sea Floor Spreading
• Hess proposed that hot, less dense material
below Earth’s crust rises toward the surface at
the mid-ocean ridges.
• Then, it flows sideways, carrying the seafloor
away from the ridge in both directions.
Sea Floor Spreading
• As the seafloor spreads apart at a midocean ridge, new seafloor is created.
• The older seafloor moves away from the
ridge in opposite directions.
• This helped explain how the crust could
move—something that the continental
drift hypothesis could not do.
• https://www.youtube.com/watch?v=hmM
lspNoZMs
Evidence of Seafloor Spreading
• In 1968, scientists
aboard the research
ship Glomar
Challenger began
gathering
information about
the rocks on the
seafloor.
• Scientists found that
the youngest rocks
are located at the
mid-ocean ridges.
Age of Seafloor Rocks