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