Transcript Continental Drift and Seafloor

Plate Tectonics
Alfred Wegners Theory
Came up with the the Theory Continental
Drift and said that there are several pieces
of evidence that support it.
The Theory of Continental drift
• All continents were once connected as
one large landmass called Pangaea.
• Landmass broke apart and drifted to their
present positions.
Pangea
• Pangea was the ancient Supercontinent
that existed when all of the continents
were connected.
• If you look at a map of the continents they
seem to fit together like a jig saw puzzle
Puzzle like Fit
Animal Fossils
• Fossils of a freshwater reptile,
Mesosaurus, were found on South
America and Africa.
• Mesosaurus could not have swam over
the Atlantic Ocean.
Plant Fossils
• Fossils of the plant, Glossopteris, were
found in Africa, India, South America, and
Antarctica which all have different
climates.
Glacial Deposits
• Eroded rocks and debris left behind by
ancient glaciers can be found in South
America, Africa, India, and Australia which
all have different climates and are not near
the poles.
Similar Rock Structures
• Rock formations identical to the American
Appalachian Mountains can be found in
Greenland and Western Europe
The Theory of Seafloor Spreading
1. On the ocean floor there are areas where
the seafloor is getting bigger.
2. Researchers used sound waves to
discover a system of underwater ridges
or mountains that can be found all over
the world.
Mid Atlantic Ridge
• This underwater chain of mountains and
volcanoes is found in the middle of the
Atlantic Ocean.
• http://www.youtube.com/watch?v=DWKW
dfJtNl0
• http://www.youtube.com/watch?v=6CsTT
mvX6mc
Why does the Seafloor Spread?
1. Hot, Less dense material below Earth’s
crust rises upward to the surfaces at the
mid ocean ridges.
2. Then, it, flows sideways, carrying the
seafloor away from the ridge.
3. As the seafloor spreads apart, magma
moves up and flows from the cracks,
cools, and forms new seafloor.
Evidence for Seafloor Spreading
• Youngest rocks are
located at mid-ocean
ridges.
Evidence for Seafloor Spreading
1. Reversal of Earth’s magnetic field are
recorded by rocks in strips parallel to
ridges.
2. These iron rich rocks point towards
magnetic North wherever it is at the time
they cool.
Discussion Question
How could seafloor spreading be related to
continental drift?
Answer
• If the Seafloor is constantly spreading
apart and moving, it will effect and move
the continents as well.
Theory of Plate Tectonics
• Earth’s crust and upper mantle are broken
into sections called plates, they move on a
plastic-like layer of the mantle.
• Plates and upper mantle form the
lithosphere.
• Plastic-like layer below is called
asthenosphere.
Types Plate Boundaries
• Divergent Plate boundaries
– Plates moving apart causing ridges and rifts
Plates Collide
• Convergent Boundaries
– Plates moving together.
– Denser plates sink under less dense plates.
– Newly formed hot magma forced upward
forms volcanic mountains
Plates collide
• Plates crumple up to form mountain
ranges.
• Earthquakes are common
More Plate boundaries
• Transform boundary
– Plates slide past one another.
– Sudden movement can cause earthquakes
Convection Current
• Hot, less dense melted rock in the earths
mantle rises and sinks in a circular motion
causing the plates to move and magma to
rise.
• This is the driving force behind Plate
Tectonics, Seafloor Spreading and
Continental Drift.