Download Theory of Continental Drift

Theory of Continental Drift
vs.
Plate Tectonics
Essential Question:
Explain the Theory of Continental Drift
and the Plate Tectonics Theory.
Looking at the world map, what do you notice
about the shape of the continents?
The thing is…the world didn’t always look
like this! It used to look like this:
This super land mass was connected into one
piece called Pangaea
Theory of Continental Drift
•Alfred Wegner – in 1910 noticed that the continents
fit like puzzle pieces, thought that at one time they
were all together as one huge continent
•Pangaea – meaning “all land”, the super continent
that existed about 200-300 million years ago
•Theory of Continental Drift – Wegner’s idea that
continents slowly moved (this idea was not excepted
by others at the time)
Theory of Continental Drift
•Evidence –
• plant and animal fossils that were identical even
though they were found on opposite sides of
the Atlantic Ocean.
• Mountain ranges and layers of rock on both
sides of the Atlantic Ocean Matched.
• Glacial Movement, fossils of plants and animals
embedded in rocks in the Arctic that were
known to be tropical.
Seafloor Spreading
• In the early 1960’s Harry Hess proposed seafloor
spreading.
• He believed that molten rock rises from the mantle along
mid ocean ridges, forcing the crust to move in opposite
directions and creating a new seafloor in the process.
• He also believed that crust was being
destroyed as it sinks into deep ocean
trenches in a process called subduction.
• Based upon these two discoveries
Alfred Wegner’s ideas were
finally accepted.
Convection Currents
• Arthur Holmes – in 1929 suggested that the Earth’s
Mantle had convection currents that were strong
enough to carry the continents around.
• Convection Currents:
• the transfer of heat by the
circulation or movement of
the heated parts of a liquid
or gas. Ocean currents,
air currents, mantle
currents
Plate Tectonics Theory
•Earth’s surface is fractured just like the shell of a
cracked egg.
•These fractures outline large plate-like chucks of the
Earth’s crust.
•These plates are floating on the mantle, drifting apart
1-10 cm yearly, sometimes colliding into other plates.
•Earthquakes and volcanoes occur on the edges.
•Mountain ranges form where continents collide.
Difference between the two
Theories…
•Plate tectonic theory states that
the entire crust moves, not just the
continents.