Earth Sciences 1022A/B Lecture 1: Earth Science Lecture January 7 2016

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JANUARY 7 2016 LECTURE
INTRODUCTION TO PHYSICAL GEOLOGY AND PLATE TECTONICS
Geology
Derived from Greek
oMeans the study of earth
Why?
oIt is important for energy and natural resources, solving environmental
problems, building cities and highways, predicting and protecting against
natural disasters like earthquakes, volcanic eruptions, landslides, floods
Uniformitarianism
oFundamental principle that the present is the key to the past
How long?
oGeologic time is measured in billions of years
Thought to be four and a half billion years old
The Canadian Shield used to be comprised of a mountain chain as
large as the Rockies
It would have taken that much time to wear it down to the
point that it is at now
Where and How?
oAfter the Big Bang (about 14 billion years ago) Earth may have formed by
the nebular theory
About 5 billion years ago a solar nebula of hydrogen and helium
gravitationally contracted into a rotating disc with our Sun at the
centre, and the planets and moons revolving around it
Within the disc, Earth evolved through many collisions of
rocky and metallic fragments into a rocky sphere divided into
a dense core, large mantle and lighter crust
oThe heavier objects migrated toward the inside of the
planet and the lighter objects migrated to the outer
circle of the planet
Plate Tectonics
The crust and uppermost mantle eventually split into rigid plates of lithosphere (sphere
of rock) that move over Earth’s surface above the soft, convecting asthenosphere (weak
sphere) by Continental Drift, based on
oFit of the continents
South America, Africa and other continents fit well together at 900 m
depth which coincides with the edge of their continental shelves
oFossil evidence
Same type and age found on continents separated by ocean basins
oRock types and structural similarities
Match when continents are fit back together
oPaleo climates
Evidence of ancient glaciations in warm areas of today show the
pattern of a single ice sheet if continents are refitted back together
Ancient coal fields that formed in tropical swamps now occur in
areas of cold climate
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