Grade 7 Science Unit 4: The Earth s Crust PLATE TECTONIC THEORY
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 supercontinent broke apart 200 million years ago.
Wegener proposed the Theory of Continental Drift which suggests that the continents change position slowly by a few cm a year. He could not explain how.
Theory of Continental Drift
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.
Convection Currents
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.
Plate Tectonics Theory CORE STSE
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. Helens May 18, 1980 Washington
Paricutin February 20, 1943 Mexico
Mt. Pinatubo June 1991 Philippians
Kilauea November 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.