grade 7 science unit 4: the earth’s crust€¦ · plate tectonics in earth’s crust when this...
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PLATE TECTONIC THEORY
Grade 7 ScienceUnit 4: The Earth’s Crust
Alfred Wegener
1880 – 1930
German meteorologist
He noticed that the continents fit together like a puzzle.
He said that at one time all continents were joined together in one large land mass, he called Pangaea.
He proposed that this super-continent broke apart 200 million years ago.
Wegener proposed the Theory of Continental Driftwhich suggests that the continents change position slowly by a few cm a year.
He could not explain how.
Th
eory
of
Co
nti
nen
tal
Dri
ft
Supporting Evidence...
Biological Evidence – Fossils
Similar fossils found on one continent have been found on others. Ex. NL and Wales
Refer to page 361
Wegener believed that at one time there had been a land bridge that has now disappeared to join continents together.
Geological Evidence – Rocks and Rock Layers
Geologists found rocks that were similar on both sides of the Atlantic Ocean. The ages of these rocks are also the same.
These rocks look as though they had been pushed up into mountains together before they were separated.
Meteorological Evidence –Climate Change
Location of coal beds. These should be found in tropical, swampy area BUT have been found in cold and moderate climates.
Glacial evidence. There are warm areas that show evidence that they were once covered in glaciers.
Accepted or Rejected?
Because he was unable to explain HOW the continents move, his theory was rejected by the scientific community.
Plate Tectonics
Developed from the earlier Continental Drift Theory due to new evidence.
New technological advances include the following...
1. Sonar: provides a more detailed picture of the sea floor. (pg. 364)
2. Magnetometers: provide evidence for sea floor spreading. (pg. 365)
3. Deep sea drilling: provides evidence for the internal structure of the crust.
(pg. 366)
Evidence Collected...
Discoveries on the sea floor showed that magma produces new crust which pushes the plates of the Earth’s crust.
The plates can be pushed in three ways.
1. Divergent boundaries: plates moves away from each other.
2. Convergent boundaries: plates move towards each other
3. Transform Boundaries: plates slide past each other.
*This idea was developed by
J. Tuzo Wilson (Canadian Scientist) during the 1960s.
New Theory...
Wilson’s ideas form a new theory in the 1970s.
Because it was discovered that the sea floor as well as the continents were moving, the plate tectonic theory was born.
This theory states that Earth’s crust is broken up into pieces, called plates that are always moving on Earth’s mantel.
Satellites are helping to measure plate movements.
Convection Currents
One explanation to the HOW.
These convection currents, that move the plates, are in the mantel.
Co
nv
ecti
on
C
urr
ents
Canadian Contributions...
J. Tuzo Wilson
He mapped out where earthquakes and volcanoes had occurred over the Earth’s surface, thereby defining the Earth’s plates.
Joseph Tyrell
Discovered dinosaur fossils in Alberta, which proved that the local climate was warmer at an earlier time.
Harold Williams
Highlighted plate tectonic activity that occurred regionally along the eastern edge of the North American continent.
CORE STSE
Plate Tectonics Theory
The shaking of the Earth
Measured using a seismograph
The Richter Scale measures the strength of the earthquake
They are the result of energy released from forces built up due to plate tectonics in Earth’s crust
When this energy is released, it travels in seismic waves.
Usually minor in our
region. They occur due
to the movement along
local faults on the floor of
the Atlantic Ocean.
Burin Peninsula, 1929,
tsunami (pg. 374)
An opening in Earth’s
crust.
Mt. St. HelensMay 18, 1980
Washington
ParicutinFebruary 20, 1943
Mexico
Mt. PinatuboJune 1991
Philippians
KilaueaNovember 24, 2007
Hawaii
The most
active
volcano
on Earth
1. At collision zones intense
pressure can melt rock
that later flows to the
surface as a volcano (the
Pacific Ocean is being
subducted under Japan)
2. Where plates separate,
molten rock flows up to
the surface (Mid-Atlantic
Ridge)
3. In area where the plates
are thin, lava can be
forced up through the
cracks to the surface.
(Hawaiian Islands)
The name given to the
volcanoes encircling the
Pacific Ocean.
Page 386-7
2. Glooscap: Mi’kmaq
legend about the
Sugarloaf Mountains.
1. Pele: Hawaiian goddess
who makes the mountains
shake and lava flow at
Kilauea.
3. Anaxagoras: Greek who
believed that volcanic
eruptions were caused
by great winds within the
earth.
4. René Decartes: French
philosopher who believed
an incandescent earth core
was the source of volcanic
heat.
Due to:
1. folding
2. faulting
3. volcanic eruptions.
A bend in rock layers.
Created when plates
collide at convergent
boundaries.
A break in rock layers.
When the rock is too
brittle to fold.
Faulting can result from
squeezing or stretching
the Earth’s crust.
When magma is forced up by pressure from deep within Earth, it can uplift the rock and create features on the surface. The magma may erupt as volcanoes.