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Alfred Wegener
• 1880 - 1930
• Doctorate in planetary
astronomy and an
interest in meteorology
• Proposed the Theory of
Continental Drift in
1915
Theory of Continental Drift
• Proposed by Alfred
Wegener - 1915
• Continents started as
a single landmass and
split apart 200 million
years ago
• Not accepted by
scientists as a valid
theory
Fossil Evidence of Continental Drift
• Jigsaw puzzle fit of
the continents
• Mesosaurus (reptile)
fossils found in
South America and
Africa
• Glossopteris (seed
fern) fossils found in
Africa and Australia
Rock Evidence of Continental Drift
• Glacier evidence in warm
weather places
• Mountains in South America and
Africa line up when the
continents are together
• Layers of rock in Antarctica,
Australia, South America, Africa
and India are similar.
• Glacial till found in places
• currently too close to the
equator for glaciers to
Connecting Glacial Evidence
Problems With Wegener’s Theory
•Could not explain
the forces that
moved the
continents
•Not possible for
the continents to
move through the
ocean floor
Technology & the 1950’s
• Development of sonar during WWII
– Mapping of the ocean floor
– Discovered ruggedness of ocean floor
• Development of submarines and submersibles
– youth of ocean floor
– Confirmation of reversals in the Earth’s magnetic field
– sea-floor spreading hypothesis
• Documentation of the locations of earthquake &
volcanic activity
Development of the Plate Tectonics
Theory
• Surface of the Earth is split into a series of
plates which float on semi-molten rock
• Convection currents in the mantle push the
plates around on the surface of the Earth
• Because of plate movements the surface of
the Earth is constantly changing
•Plate boundaries are where Earthquakes,
volcanoes and mountain ranges occur
• Crust is made at mid-ocean ridges
• Crust is destroyed at subduction zones
Earthquake Zones
Global Distribution of Earthquakes
Sea-Floor Spreading
Harry Hess 1906-1969
•Professor of Geology at Princeton
•Conducted echo-sounding surveys
of the ocean floor during WWII
•magma oozes up along mid ocean ridges and creates new sea floor
Divergent
Boundary
• Mid-Atlantic Ridge
• Caused by sea-floor
spreading
• Rate of spreading
averages 2.5 cm/yr
• Has taken 100-200
million years to create
the Atlantic Ocean
Types of Plate Boundaries
Convergent Plate Boundary
Oceanic/Continental Plates
Convergent Plate Boundary
Oceanic/Oceanic Plates
Convergent Plate Boundary
Continental/Continental Plates
Raising the Himalayas
Formation of the Himalayas
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