Continental Drift/Plate
Tectonics
Who is the Scientist that
developed the ideas that
led to the theory of
Continental Drift?
Alfred
Wegener
Alfred Wegener
“Doesn’t the east
coast of South
America fit exactly
against the west coast
of Africa, as if they had
once been joined”?
Alfred
Wegener
 Hypothesized the existence of Pangea – This very large single
landmass of continents existed millions of years ago.
 This land mass covered about one-third of Earths surface
 This land mass formed about 300 million years ago and began to
split up about 200 million years
What is Continental
Drift?
 Proposed the idea of continental drift!
Alfred
Wegener
 Continental Drift is the idea that continents slowly move over the
earths surface.
What kinds of evidence
did Wegener use to
develop his hypothesis?
 Climatological evidence
Evidence
 Fossil evidence
 Land features
 Glacial evidence
 Temperate tree fossils under polar ice caps
Climatological
 Coral Reefs
 Coal in antartica
 In 1911 the same type of plant and animal fossils are found in
rocks of the same age but are on continents that are now widely
separated.
Fossil Evidence
 Glossopteris and Mesosaurus are examples. They are large reptiles
that are unable to swim. The land masses must have been
connected at one time.
Land feature
evidence
 Appalachian mountains are just like the mountain ranges in
eastern Greenland, Iceland, Great Britain, and Norway.
 The same Rock types, structures, and ages now on opposite sides
of the Atlantic Ocean
 Continental slope (elevation above sea level) match up between
continents across oceans.
What was
Alfred's
hypothesis
missing?
 Wegener developed the idea that the continental plates are
moving.
 What he lacked is a explanation of how the continental plates
move.
What force is
responsible for tectonic
plate movement?
Convection in
the mantle
moves the
plates!!
Plate Tectonics
 Wegener proposed the idea that continental plates are slowly
moving.
Plate Tectonics
 The theory of Plate Tectonics states that the earths lithosphere is
made up of plates (both continental and oceanic) that are moving
due to convection currents in the mantle.
 The way these plates interact are responsible for many of earths
features that we can observe.
What are the three
types of Plate
boundaries ?
Plate
Boundaries
 Convergent
 Divergent
 Transform
Convergent
Plate
Boundaries
 Convergent boundaries are when two plates collide with one
another
 Can be oceanic plate with continental plate, two continental
plates, or two oceanic plates.
 Each combination result in different land features
Oceanic plate
–Oceanic plate
 Oceanic plates are thin and really dense.
OceanicOceanic
 One of the ocean plates will go under the other and form a
subduction zone
 Subduction zones result in Volcanos due to the melting of the
crust of the suducted plate. (ie. islands form)
 LAND FORMS – Deep ocean Trench and volcanic islands
ContinentalOceanic
Continental –
Oceanic
 Oceanic curst is a lot denser than the continental crust and forms
another subduction zone.
 LAND FORM- Volcanic Mountain ranges
Continental –
Continental
ContinentalContinental
 Both plates are of the same density. Neither wants to go under the
other.
 LAND FORM- Large mountain ranges – (ie. Himalayan Mountains)
No volcanos
Divergent
 Plates move away from each other
Divergent
 Magma from the mantle moves up and fills the space between the
plates.
 Land Form- Two ocean plates form a Mid-Ocean Ridge
 Land Form- Two continental plates form a continental Rift.
Transform
 Two plates are sliding past each other
Transform
 Major outcome from this plate boundary is Earthquakes( ie.
California’s )
What are the three
types of evidence for
sea floor spreading?
 Molten Material- Unique rock structures (looks like toothpaste
coming out of the tube) form when magma cools extremely fast.
This shows plates are pulling apart and magma from mantle is
constantly coming up and filling gap.
Sea Floor
Spreading?
 Magnetic Stripes- Earths magnetic poles reverse about every
million years. As the magma cooled the iron in it lined up towards
the magnetic pull. This created “magnetic memory”. When we
look at the ocean floor we can see strips of different magnetic field
showing that the curst is continuously being created.
 Drilling samples – Shows that the farther you get away from a
ocean ridge the older the rocks are.