Continental Drift

Continental Drift

Middle School

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Learning Objectives

• Define the theory of continental drift and the supercontinent Pangaea.

• Describe the four main types of evidence for Alfred Wegener's theory.

• Explain why Wegener's theory was initially rejected by the scientific community.

• Understand the key discoveries that led to the acceptance of continental drift.

Key Vocabulary

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Continental Drift

This is the slow, steady movement of Earth's continents over the ocean floor over millions of years.

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Pangaea

Pangaea was a supercontinent that existed millions of years ago, joining all of Earth's continents together.

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Glossopteris

An extinct plant fossil found on different continents, providing evidence that they were once connected.

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Mid-Ocean Ridge

A large underwater mountain range where new ocean floor is created by cooling magma from the mantle.

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Convection Currents

The circular motion of magma in the mantle that transfers heat and drives the movement of tectonic plates.

Wegener's Big Idea

• South America and Africa's coastlines looked like they could fit together.

• The continents were once a giant supercontinent called Pangaea.

• This movement is very slow, like how your fingernails grow.

Multiple Choice

What is the name of the supercontinent that Alfred Wegener proposed existed before the continents drifted apart?

• Pangaea

• Laurasia

• Gondwanaland

• Eurasia

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Fossil Evidence

• Wegener found matching plant and animal fossils on continents separated by vast oceans.

• Glossopteris fern seeds were too heavy to be carried by wind across an ocean.

• Mesosaurus was a freshwater reptile that could not swim across the salty Atlantic Ocean.

• Land animals like Cynognathus and Lystrosaurus could not have crossed the wide oceans.

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Multiple Choice

Why was the discovery of Mesosaurus fossils in both South America and South Africa considered evidence for continental drift?

• The fossils were carried by ocean currents.

• Mesosaurus was a freshwater reptile that could not have swum across the salty Atlantic Ocean.

• The fossils were from different time periods.

• Mesosaurus was a powerful swimmer that crossed the Atlantic.

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Rock and Climate Clues

• Rocks on Brazil's coast matched the type and age of African rocks.

• The Appalachian Mountains align with ranges in Greenland, Ireland, and Norway.

• Wegener found evidence of ancient glaciers in current-day tropical regions.

• Tropical plant fossils and coal were found in Antarctica's extremely cold climate.

Multiple Choice

What climate evidence did Wegener use to support his theory?

• Finding evidence of glaciers in tropical areas and tropical plant fossils in polar areas.

• Noticing that all continents have similar weather patterns today.

• Discovering fish fossils on mountaintops.

• Finding desert sand in Antarctica.

Rejection and Acceptance

• Wegener's theory was rejected as he could not explain the force moving continents.

• New evidence of sea-floor spreading was discovered by mapping the ocean floor.

• Plate tectonics showed convection currents in the mantle move the Earth's plates.

Multiple Choice

What was the primary reason Alfred Wegener's Continental Drift theory was initially rejected?

• He could not explain the force that caused the continents to move.

• He did not have enough fossil evidence.

• Scientists did not believe that Pangaea could exist.

• The continents did not fit together perfectly.

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The Breakup of Pangaea

• Pangaea existed about 300 million years ago, centered over modern-day Africa.

• This supercontinent began to break apart about 200 million years ago.

• By 180 million years ago, it split into Laurasia and Gondwanaland.

• The continents continued to move to the positions they have today.

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Multiple Choice

Pangaea first split into which two smaller continents?

• Laurasia and Gondwanaland

• Antarctica and Australia

• Africa and Eurasia

• North America and South America

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Common Misconceptions

Misconception	Correction
Continents do not move.	Continents are always moving, but very slowly, about as fast as your fingernails grow.
Alfred Wegener was a geologist.	Wegener was a meteorologist and explorer, not a geologist.
The ocean floor is a flat, empty basin.	The ocean floor has huge features, like the world's longest mountain chain.
Land bridges explain how animals crossed oceans.	Land bridges don't explain fossils found on widely separated continents like Australia and Antarctica.

Multiple Choice

How did matching the rock types and mountain ranges of the Appalachian Mountains with ranges in Greenland and Europe support the theory of continental drift?

• It showed that mountains can form underwater.

• It proved that the rocks were all the same age.

• It suggested these landmasses were once connected as a single mountain chain that later split apart.

• It proved that the Atlantic Ocean is shrinking.

Multiple Choice

What is the relationship between sea-floor spreading and continental drift?

• Sea-floor spreading is the process that creates new crust, providing the mechanism for how continents move.

• Continental drift causes sea-floor spreading.

• They are two competing theories that contradict each other.

• They both describe the process of mountains forming on land.

Multiple Choice

Based on the evidence for continental drift, what can you infer about Earth's geography in the distant future?

• The continents will continue to move, and the map of the world will look different than it does today.

• The Atlantic Ocean will close, and the Pacific Ocean will widen.

• The continents will move back together to reform Pangaea.

• The continents will stop moving and remain in their current positions.

Multiple Choice

Analyze the journey of the Continental Drift theory from rejection to acceptance. What does this reveal about the nature of scientific progress?

• Only geologists are allowed to propose theories about the Earth.

• Science is a process that evolves; theories can be rejected at first but later accepted when new evidence or technology provides a missing explanation.

• Scientific progress depends on a single, revolutionary idea.

• Scientific theories are accepted immediately if they have good evidence.

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Summary

• Alfred Wegener proposed that all continents were once a single supercontinent called Pangaea.

• Evidence for his theory included matching fossils, rocks, and continental shapes.

• The theory was not accepted at first as it lacked an explanation for movement.

• The later theory of Plate Tectonics explained how and why the continents move.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4