GEG-1 Lecture Notes - Lecture 2: Plate Tectonics, Physical Geography, Geologic Time Scale
Physical Geography
Notes
Joseph Yang
● By 1968, a new theory, known as plate tectonics, was developed
○ Plate tectonics is the theory that helps explain most geological processes
○ States that the earth’s outer shell is made up of about twenty plates
○ Most of these plates are made up of both a continent and an ocean
○ They are moving over a weak layer of hot rock, several kilometres below the earth’s
surface, which moves like slow-moving plastic
○ The unequal distribution of heat within the earth causes convection currents to
move the plates
■ No one fully understands the forces that cause the plates to move over this
weak layer
■ Convection cells are caused by the uneven temperatures inside the earth
■ They are the driving force that moves the plates
■ As two plates move apart, magma comes up from the earth, the sea floor
spreads, and a ridge is formed
■ As two plates collide, one plate descends under the other, creating a trench
○ The movement of the earth’s plates has shaped Canada in many ways
■ The mountain chains on the east and west coasts were formed as a result of
plates bumping close together
○ Plate tectonics have also played a role in forming Canada’s fossil fuels
■ Oil, gas, and coal were formed as a result of events which took place when
Canada’s land mass was located in a warmer, tropical climate
Canada’s Geologic History
● Besides plate tectonics, the earth’s physical landscape is also partly the result of conflict
between forces that build up the land higher and those that wear it down
○ Land that is violently pushed upward by great forces within the earth may form
mountains
○ Mountains, in turn, are slowly and continuously worn down by wind, rain, running
water, and ice
■ This wearing down is called erosion
○ Sometimes, one force is stronger than the other
■ This conflict has taken place over hundreds of millions of years, and forms
the story of the earth’s geologic history
■ We can find out about earth’s early physical history by carefully analyzing
landforms, rocks and fossils
○ To make geologic time easier to understand, geologists have divided the earth’s
history into four time periods called eras
■ Each era represents a time of major sediment deposition and earth
movement
■ Precambrian era:
● The hot earth cooled to form mounds of rock called shields
● Volcanic activity continued to change the landscape
■ Paleozoic era
Document Summary
By 1968, a new theory, known as plate tectonics, was developed. Plate tectonics is the theory that helps explain most geological processes. States that the earth"s outer shell is made up of about twenty plates. Most of these plates are made up of both a continent and an ocean. They are moving over a weak layer of hot rock, several kilometres below the earth"s. The unequal distribution of heat within the earth causes convection currents to. No one fully understands the forces that cause the plates to move over this surface, which moves like slow-moving plastic move the plates weak layer. Convection cells are caused by the uneven temperatures inside the earth. They are the driving force that moves the plates. As two plates move apart, magma comes up from the earth, the sea floor spreads, and a ridge is formed. As two plates collide, one plate descends under the other, creating a trench.
