Continental Drift
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Continental DriftContinental Drift
Plate TectonicsPlate Tectonics
The lithospheric plates float on top of the liquid asthenosphere.
This causes the plates to move around slowly.
Over a long period of time, they can move large distances.
The lithospheric plates float on top of the liquid asthenosphere.
This causes the plates to move around slowly.
Over a long period of time, they can move large distances.
DiscoveryDiscovery
Alfred Wegener was the first person to come up with the concept of Continental Drift.
He suggested that the continents formed from a super-continent called Pangaea, breaking apart about 200 million years ago
Alfred Wegener was the first person to come up with the concept of Continental Drift.
He suggested that the continents formed from a super-continent called Pangaea, breaking apart about 200 million years ago
We are now going to look at the pieces of
Evidence Wegener used to prove his theory…
We are now going to look at the pieces of
Evidence Wegener used to prove his theory…
1. Jigsaw Puzzle1. Jigsaw Puzzle
Wegener’s first clue was the perfect fit of the African/South American Coastlines
Wegener’s first clue was the perfect fit of the African/South American Coastlines
2. Geological Structure
2. Geological Structure
Analysis of rocks suggested similarities between continents (similar age/type)
Some mountain ranges end at one coastline and begin at another
Analysis of rocks suggested similarities between continents (similar age/type)
Some mountain ranges end at one coastline and begin at another
3. Fossil Evidence3. Fossil Evidence
This is the best support for Wegener’s theory
Similar fossils have been found in different locations across the world
Eg. MesosaurusThe only explanation: all the land was once connected
This is the best support for Wegener’s theory
Similar fossils have been found in different locations across the world
Eg. MesosaurusThe only explanation: all the land was once connected
4. Glacier Evidence4. Glacier Evidence
(Paleoglaciation)When glaciers move, they leave distinctive patterns
(large U shaped valleys, sediments, deep scratches)
All of these were found in tropical areas
(Paleoglaciation)When glaciers move, they leave distinctive patterns
(large U shaped valleys, sediments, deep scratches)
All of these were found in tropical areas
5. Coal Beds5. Coal Beds
Coal beds form from the decomposition of tropical swamps
So how can there be coal beds in Antarctica?
Coal beds form from the decomposition of tropical swamps
So how can there be coal beds in Antarctica?
The best answer for the coal/glacier evidence is that the continents must have been in completely different locations,
which gave them completely different
climates!
The best answer for the coal/glacier evidence is that the continents must have been in completely different locations,
which gave them completely different
climates!
The only question Wegener couldn’t answer
was…
The only question Wegener couldn’t answer
was…
How can continents move if they are large and made out of solid rock?
Plate tectonics and the soft asthenosphere were unknown at the time so he had no answer…
How can continents move if they are large and made out of solid rock?
Plate tectonics and the soft asthenosphere were unknown at the time so he had no answer…
Plate TectonicsPlate Tectonics
Proof – MagnetismProof – Magnetism
The discovery of the mid-atlantic ridge (which is a mountain range under water)
It has bands of opposite polarity called magnetic striping
See p512
The discovery of the mid-atlantic ridge (which is a mountain range under water)
It has bands of opposite polarity called magnetic striping
See p512
Explanation of Striping
Explanation of Striping
Earth is like a bar magnet. It flips polarity every 500,000 years.
As the ridge opens, it makes new rock. As the rock hardens, its domains line up with the earth’s magnetic field.
Earth is like a bar magnet. It flips polarity every 500,000 years.
As the ridge opens, it makes new rock. As the rock hardens, its domains line up with the earth’s magnetic field.
As the earth’s magnetic polarity flips, so does that of the rock.
This creates magnetic stripes.
As the earth’s magnetic polarity flips, so does that of the rock.
This creates magnetic stripes.
Sea Floor SpreadingSea Floor Spreading
Harry HessMagma is less dense so it rises through breaks in the sea floor
We call this spot a spreading ridge
It cools and hardens, making new sea floor
Harry HessMagma is less dense so it rises through breaks in the sea floor
We call this spot a spreading ridge
It cools and hardens, making new sea floor
This process continues, pushing older rock aside. We call this process sea floor
spreading
This process continues, pushing older rock aside. We call this process sea floor
spreading
Plate Tectonic TheoryPlate Tectonic Theory
J. Tuzo Wilson Island arcs form when plates move over stationary hot spots
This is an area where molten rock rises.
He helped form the Plate Tectonic Theory
J. Tuzo Wilson Island arcs form when plates move over stationary hot spots
This is an area where molten rock rises.
He helped form the Plate Tectonic Theory
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