Unit E Lesson E10 Continental Drift
Completion requirements
Lesson E10: Continental Drift
Video Lesson
We know the ground beneath our feet can shift, but usually we imagine an earthquake or landslide causing these movements. The amazing reality, though, is that almost every part of Earth's crust is always moving - just very slowly. Over millions and billions
of years these tiny movements can add up to some amazing transformations to the world.
Lesson E10: Continental Drift
Earth's Puzzling Surface
Nobody had a very good idea of the appearance of Earth’s surface before explorers sailed around the world and drew maps of their adventures. Coastlines, islands, rivers, and mountains were added to charts (maps) that revealed the planet for the first time. Soon, someone noticed that the continents on the maps looked like a puzzle and that rocks, plants, and animals from these distant lands were sometimes very similar. Various scientists began to suggest that the continents may be moving, or changing places with each other, or doing something strange that they could not explain based on the patterns they were observing. Without evidence, however, no one could prove this was true. These were the early days of the theory of continental drift.
Nobody had a very good idea of the appearance of Earth’s surface before explorers sailed around the world and drew maps of their adventures. Coastlines, islands, rivers, and mountains were added to charts (maps) that revealed the planet for the first time. Soon, someone noticed that the continents on the maps looked like a puzzle and that rocks, plants, and animals from these distant lands were sometimes very similar. Various scientists began to suggest that the continents may be moving, or changing places with each other, or doing something strange that they could not explain based on the patterns they were observing. Without evidence, however, no one could prove this was true. These were the early days of the theory of continental drift.
Reading for This Lesson
Science in Action 7
Materials:
Science in Action 7
Reading: Pages 392–394, 401
Materials:
No other materials are required for this lesson.
Figure E.3.10.1 – Early scientists began to wonder about the shapes of the continents as soon as the earliest maps were drawn. This map is from the year 1570.
Continental Drift
Earth’s crust consists of tectonic plates that float on the convection currents of the magma in the mantle below the crust. All the land, oceans, mountains, and seas are on these plates. The plates float slowly in various directions, sometimes colliding with each other, and sometimes drifting apart. The meeting of these plates results in volcanoes and earthquakes.
Imagine you and your friends playing in a swimming pool, each on a floating mat. Sometimes, you float into each other gently and you link arms to form a bigger mat. Sometimes, you play demolition derby and the mats crash together and pile high into the air. Sometimes, one mat slides under another when they meet.
Earth’s crust consists of tectonic plates that float on the convection currents of the magma in the mantle below the crust. All the land, oceans, mountains, and seas are on these plates. The plates float slowly in various directions, sometimes colliding with each other, and sometimes drifting apart. The meeting of these plates results in volcanoes and earthquakes.
Imagine you and your friends playing in a swimming pool, each on a floating mat. Sometimes, you float into each other gently and you link arms to form a bigger mat. Sometimes, you play demolition derby and the mats crash together and pile high into the air. Sometimes, one mat slides under another when they meet.
These mat behaviours are similar to tectonic plate behaviours as they move slowly about Earth’s surface with varying force because of size and other factors.
In the past two hundred years, scientists have used various evidence to develop ideas of how tectonic plates move and where they have been in the past. This has led to the idea of continental drift.
This idea suggests that Earth’s tectonic plates are in constant motion and that, in the distant past, all continents crashed together to form a single supercontinent that has been named Pangaea. Likely, this has happened more than once, and it might happen again in the distant future – not tomorrow!
Developing the Theory
In the past two hundred years, scientists have used various evidence to develop ideas of how tectonic plates move and where they have been in the past. This has led to the idea of continental drift.
This idea suggests that Earth’s tectonic plates are in constant motion and that, in the distant past, all continents crashed together to form a single supercontinent that has been named Pangaea. Likely, this has happened more than once, and it might happen again in the distant future – not tomorrow!
Developing the Theory
Figure E.3.10.2 – By 1869, maps showed some remarkable similarities in the shapes of the continents.
Figure E.3.10.3 – Early explorers created maps for later explorations.
Explorers throughout human history have lived in almost every corner of the world, dived into the ocean depths, and even flown to the Moon. Not only do many explorers like an adventure, but they like to make notes and maps of their journeys and
their findings. Humans like to explore.
About 600 years ago, several European countries began to explore the
world by sponsoring sailing ships to find new lands, exciting products,
and routes to expand trade. In the early 1400s, countries such as
Portugal, Spain, France, England, and Holland began an explosive period
of exploration named the “Age of Discovery”. Undoubtedly, other
explorers had been travelling for many years before this, including the
Chinese in the South Pacific and the Vikings in the North Atlantic, but
never had so much of the world been covered so quickly and so
thoroughly. This was the first time that detailed maps were made of
these travels.
These maps were made for various reasons, but likely the study of geology was not one of them. However, geologists were very interested to see some of the shapes and patterns shown on these early maps. People who travelled on some of these voyages or who saw evidence brought back to Europe on the ships noticed similarities among some plants, animals, and even fossils from these newly discovered lands.
These maps were made for various reasons, but likely the study of geology was not one of them. However, geologists were very interested to see some of the shapes and patterns shown on these early maps. People who travelled on some of these voyages or who saw evidence brought back to Europe on the ships noticed similarities among some plants, animals, and even fossils from these newly discovered lands.
Figure E.3.10.4 – This 1858 drawing shows a possible match between South America and Africa.
Figure E.3.10.5 – Wegener was a geologist who also studied weather.
Alfred Wegener
After the beginning of the Age of Discovery, various geologists began to wonder about Earth’s continents. Ideas proposed by geologists included continents exchanging places, the Earth shrinking or expanding, and oceans and seas drying up and refilling. A very popular opinion was that the continents did not move and all the evidence collected was just a coincidence.
Then, in 1912, Alfred Wegener, a German geologist, published his theory of continental drift. He proposed that the continents were floating slowly on Earth’s surface, and sometime in the past continents such as South America and Africa had been very close together if not actually joined as one supercontinent. He used evidence and ideas from earlier scientists and explorers to explain his theory, but it was dismissed by almost everyone as impossible. His theory of continental drift was not accepted until many years after his death.
Wegener was right, but he had no way to prove it. His evidence seemed to support the concept of continents drifting together and apart, but nobody, including Wegener, could explain how this could happen. Not until sophisticated equipment could collect data about both the movement of the continents and the structure of Earth below the crust could Wegener’s idea be confirmed and accepted.
After the beginning of the Age of Discovery, various geologists began to wonder about Earth’s continents. Ideas proposed by geologists included continents exchanging places, the Earth shrinking or expanding, and oceans and seas drying up and refilling. A very popular opinion was that the continents did not move and all the evidence collected was just a coincidence.
Then, in 1912, Alfred Wegener, a German geologist, published his theory of continental drift. He proposed that the continents were floating slowly on Earth’s surface, and sometime in the past continents such as South America and Africa had been very close together if not actually joined as one supercontinent. He used evidence and ideas from earlier scientists and explorers to explain his theory, but it was dismissed by almost everyone as impossible. His theory of continental drift was not accepted until many years after his death.
Wegener was right, but he had no way to prove it. His evidence seemed to support the concept of continents drifting together and apart, but nobody, including Wegener, could explain how this could happen. Not until sophisticated equipment could collect data about both the movement of the continents and the structure of Earth below the crust could Wegener’s idea be confirmed and accepted.
Watch More
Alfred Wegener
Alfred Wegener had an idea that proved to be true, but it was not believed when he announced it. Think about why it took so long for his ideas to be accepted by science.
Alfred Wegener had an idea that proved to be true, but it was not believed when he announced it. Think about why it took so long for his ideas to be accepted by science.
Evidence
The earliest and strongest evidence that continental drift had occurred was found along the shores of Africa and South America. The maps of these two continents fit together like a jigsaw puzzle. These two continents have some of the same plant and animal species as well as fossils although their coastlines are now 2500 km apart.
For example, fossils of the freshwater reptile Mesosaurus have been found in both Brazil (South America) and South Africa. Mesosaurus lived about 250 million years ago. Even more widely found were fossils of the fern Glossopteris, which also lived 250 million years ago. This suggests that several continents may have been bunched together in the past.
Then, more evidence was found connecting other locations on various continents. The rocks and fossils of the Appalachian Mountains in the eastern United States are about 500 million years old. Those rocks and fossils occur also in Canada’s maritime provinces, in parts of Great Britain, and in Morocco on the northwest coast of Africa.
Glaciers can leave behind evidence as well, such as deep gouges in the bedrock and deposits of unique rocks and minerals. Unique glacial evidence that ties together several continents has been found throughout several continents.
The earliest and strongest evidence that continental drift had occurred was found along the shores of Africa and South America. The maps of these two continents fit together like a jigsaw puzzle. These two continents have some of the same plant and animal species as well as fossils although their coastlines are now 2500 km apart.
For example, fossils of the freshwater reptile Mesosaurus have been found in both Brazil (South America) and South Africa. Mesosaurus lived about 250 million years ago. Even more widely found were fossils of the fern Glossopteris, which also lived 250 million years ago. This suggests that several continents may have been bunched together in the past.
Then, more evidence was found connecting other locations on various continents. The rocks and fossils of the Appalachian Mountains in the eastern United States are about 500 million years old. Those rocks and fossils occur also in Canada’s maritime provinces, in parts of Great Britain, and in Morocco on the northwest coast of Africa.
Glaciers can leave behind evidence as well, such as deep gouges in the bedrock and deposits of unique rocks and minerals. Unique glacial evidence that ties together several continents has been found throughout several continents.
Figure E.3.10.6 – Wegener found fossil evidence of continental drift that supported the findings of Snider-Pellegrini and others for many years previously.
Even some living organisms provide evidence of continental drift. Identical earthworm families, which would have no way to travel across oceans, have been found in South America and in Africa.
Try It!
Evidence of Continental Drift
DOWNLOAD this document. It will help you examine how various types of evidence helped to support the idea of continental drift.
Instructions:
1. Open the file you downloaded. It is called “A Plate Tectonic Puzzle” and is available courtesy of the American Museum of Natural History.
2. Print the Plate Tectonic puzzle. If you want to save paper, you can print only pages 3, 4, and 5.
3. Cut out the continents and the legend on page 5.
DOWNLOAD this document. It will help you examine how various types of evidence helped to support the idea of continental drift.
Instructions:
1. Open the file you downloaded. It is called “A Plate Tectonic Puzzle” and is available courtesy of the American Museum of Natural History.
2. Print the Plate Tectonic puzzle. If you want to save paper, you can print only pages 3, 4, and 5.
3. Cut out the continents and the legend on page 5.
4. Paste the legend to the bottom of page 4. Place the continents carefully on the black Earth (circle) on page 4 so they match the positions of the continents on page 3, which is Pangaea. Trace lightly around the edges of the continents if you can, or
trace through the map on page 3 placed beneath page 4.
5. Move the continents to their current position by sliding and rotating them slowly into place on the same map.
5. Move the continents to their current position by sliding and rotating them slowly into place on the same map.
Think about the following questions very carefully. Then, type or write your answers. After you have your answers, click the questions for feedback.
India, Australia, and Arabia appear to have moved furthest.
Antarctica (not shown), North America, Asia, Africa, and South America have not moved very far.
India has rotated more than 90°, and Africa and Arabia about 45°.
The Pangaea map shows plant and animals fossils, rocks, and deserts that were once close together but are now far apart.
Figure E.3.10.7 – Technology such as GPS allows us to track exact direction and speed of the continents.
Figure E.3.10.8 – The continents are parts of most of the major tectonic plates that move slowly on Earth’s surface.
Measurement
The ability to measure Earth and the movement of its tectonic plates confirmed continental drift. Now, satellites can measure the speed and direction of movement of the plates very accurately. Seismic devices have revealed Earth’s layers and the fluid mantle that allows the continents to float and drift as Wegener proposed. The composition and age of rocks and fossils can be analyzed and compared to match with other rocks from other continents.
Even magnetism provides evidence for continental drift. The Earth is a giant magnet. The iron found in its outer core forms a magnetic field as the liquid magma flows around the solid inner core. When new igneous rocks are formed, any iron they have aligns with Earth’s magnetic field as the rock cools. However, Earth’s magnetic field is always changing position at a constant rate. By examining the iron in magnetic rocks, geologists can reconstruct what Earth’s surface must have been like when the rock was formed.
The Past
What has all this evidence and all these measurements revealed about continental drift and Earth’s past? Several important ideas emerge from this theory:
The ability to measure Earth and the movement of its tectonic plates confirmed continental drift. Now, satellites can measure the speed and direction of movement of the plates very accurately. Seismic devices have revealed Earth’s layers and the fluid mantle that allows the continents to float and drift as Wegener proposed. The composition and age of rocks and fossils can be analyzed and compared to match with other rocks from other continents.
Even magnetism provides evidence for continental drift. The Earth is a giant magnet. The iron found in its outer core forms a magnetic field as the liquid magma flows around the solid inner core. When new igneous rocks are formed, any iron they have aligns with Earth’s magnetic field as the rock cools. However, Earth’s magnetic field is always changing position at a constant rate. By examining the iron in magnetic rocks, geologists can reconstruct what Earth’s surface must have been like when the rock was formed.
The Past
What has all this evidence and all these measurements revealed about continental drift and Earth’s past? Several important ideas emerge from this theory:
Figure E.3.10.9 – This map shows approximately where modern countries would have been located on Pangea. Map by
Massimo Pietrobon.
-
Earth has two types of crust: continental tectonic plates and oceanic tectonic plates. This is very important because the two types of crust must interact to allow the continents to move in the ways they do.
-
Ten large tectonic plates are made of combinations of continental crust and oceanic crust. The largest plate is the Pacific Plate, which is made of oceanic crust only. All other major plates are combinations of oceanic crust and continental crust.
-
The continents were all joined as a supercontinent (named Pangaea) that formed about 300 million years ago. About 175 million years ago Pangaea began to break.
-
Pangea broke into two smaller supercontinents named Laurasia (modern North America, Europe, and most of Asia) and Gondwana (modern South America, Africa, Australia, Antarctica, and India).
-
Gondwana split apart soon after Pangea broke up. Antarctica stayed where it is now, South America moved west, and Australia moved east. Africa started moving slowly north, and India moved faster to the northeast. About 50 million years ago, Africa crashed
(in very slow motion, remember!) into Europe, and India crashed into Asia. Africa is still crashing slowly into Europe, and India is still crashing into Asia. The India-Asia collision produced the Himalayas, and the Africa-Europe collision resulted
in the Alps.
-
Laurasia broke apart, almost rejoined, then finished breaking apart 55 million years ago. North America, Greenland, and Eurasia moved apart at this time. This occurred at roughly the same time that India was crashing into Asia to form the Himalayas and
the dinosaurs were wiped out in a
mass extinction.
-
The continents have been joined together and have broken apart several times in the past – before Pangaea. In fact, evidence seems to point to a supercontinent forming every 300 to 500 million years throughout Earth’s history. Pangaea is the name given
to the supercontinent that formed 300 million years ago. The supercontinent that formed 600 million years ago was given the name Pannotia. The supercontinent that formed 1 billion years ago was given the name Rodinia.
Try It!
To Pangaea and Back Again
Try this simple interactive website to see how the continents have drifted from where they were in Pangaea 300 million years ago. This website activity requires Flash, if you can't get it to work on your computer, don't worry, this activity is optional.
Instructions:
1. You will be clicking, dragging, and rotating the continents so they fit into a “Pangaea puzzle” template. You can see this template by clicking on the “Pangaea On” button. A reset button allows you to go back to today’s continental positions.
2. Click a continent to select it. Drag it to where it fits with the other continents, or match it to its position on the Pangaea template.
3. To rotate the continent, select it, then use the circular wheel to rotate it.
4. Leave the continents in their Pangaea position when you are satisfied with your work.
Try this simple interactive website to see how the continents have drifted from where they were in Pangaea 300 million years ago. This website activity requires Flash, if you can't get it to work on your computer, don't worry, this activity is optional.
Instructions:
1. You will be clicking, dragging, and rotating the continents so they fit into a “Pangaea puzzle” template. You can see this template by clicking on the “Pangaea On” button. A reset button allows you to go back to today’s continental positions.
2. Click a continent to select it. Drag it to where it fits with the other continents, or match it to its position on the Pangaea template.
3. To rotate the continent, select it, then use the circular wheel to rotate it.
4. Leave the continents in their Pangaea position when you are satisfied with your work.
Think about the following questions very carefully; then, type or write your answers. After you have your answers, click the questions for feedback.
India, Australia, and Arabia appear to have moved furthest.
Antarctica (not shown), North America, Asia, Africa and South America have moved very little.
Probably India, but it has crashed into Asia. Australia has moved far but it has not crashed into another continent yet.
India has rotated more than 90°, and Africa and Arabia about 45°.
India, Africa, and Arabia have collided with Asia.
Figure E.3.10.10 – Pangaea broke apart and the continents moved to where they now reside over a span of 200 million years.
The Future
The speed that the continents move is about a centimetre or two every year. India was moving 5 cm per year until it crashed into Asia, and Australia is currently moving that fast as it slowly begins to crash into Southeast Asia. Other than Antarctica, all continents are moving at various speeds and in various directions. What does all of this movement mean for the future?
The collision between the African plate and the Eurasian plate will close the Mediterranean Sea. Many earthquakes will occur in Italy, Greece, and northern Africa. The Alps and Pyrenees mountains will continue to grow taller as a result. India will continue to crash into Asia, and the Himalayas will grow. Fifty million years from now Australia will likely hit the edge of the Eurasia plate and spin into China. The Atlantic Ocean will grow wider, and the Pacific Ocean will become smaller as North and South America move west. Possibly, 250 million years from now all continents will once again join to form another supercontinent – and the cycle will continue.
The speed that the continents move is about a centimetre or two every year. India was moving 5 cm per year until it crashed into Asia, and Australia is currently moving that fast as it slowly begins to crash into Southeast Asia. Other than Antarctica, all continents are moving at various speeds and in various directions. What does all of this movement mean for the future?
The collision between the African plate and the Eurasian plate will close the Mediterranean Sea. Many earthquakes will occur in Italy, Greece, and northern Africa. The Alps and Pyrenees mountains will continue to grow taller as a result. India will continue to crash into Asia, and the Himalayas will grow. Fifty million years from now Australia will likely hit the edge of the Eurasia plate and spin into China. The Atlantic Ocean will grow wider, and the Pacific Ocean will become smaller as North and South America move west. Possibly, 250 million years from now all continents will once again join to form another supercontinent – and the cycle will continue.
Figure E.3.10.11 – We can predict where the continents might be 300 years into the future based on our understanding of continental drift and plate tectonics.
Watch More
Continental Drift in the Past and Future
Watch as the continents form and then drift from the time of Earth’s formation until 300 million years into the future. You can also watch the past and future on a globe that you can turn at this link.
Watch as the continents form and then drift from the time of Earth’s formation until 300 million years into the future. You can also watch the past and future on a globe that you can turn at this link.
Make sure you have understood everything in this lesson. Use the Self-Check below, and the Self-Check & Lesson Review Tips to
guide your learning.
Unit E Lesson 10 Self-Check
Instructions
Complete the following 6 steps.
Don't skip steps – if you do them in order, you will confirm your
understanding of this lesson and create a study bank for the future.
- DOWNLOAD the self-check quiz by clicking here.
- ANSWER all the questions on the downloaded quiz in the spaces provided. Think carefully before typing your answers. Review this lesson if you need to. Save your quiz when you are done.
- COMPARE your answers with the suggested "Self-Check Quiz Answers" below. WAIT! You didn't skip step 2, did you? It's very important to carefully write out your own answers before checking the suggested answers.
-
REVISE your quiz answers if you need to. If you answered all the questions correctly, you can skip this step. Revise means to change, fix, and add extra notes if you need to. This quiz is NOT FOR MARKS, so it is perfectly OK to correct
any mistakes you made. This will make your self-check quiz an excellent study tool you can use later.
- SAVE your quiz to a folder on your computer, or to your Private Files. That way you will know where it is for later studying.
- CHECK with your teacher if you need to. If after completing all these steps you are still not sure about the questions or your answers, you should ask for more feedback from your teacher. To do this, post in the Course Questions Forum, or send your teacher an email. In either case, attach your completed quiz and ask; "Can you look at this quiz and give me some feedback please?" They will be happy to help you!
Self-Check Time!
|
|
Self-Check Quiz Answers
Click each of the suggested answers below, and carefully compare your answers to the suggested answers.
If you have not done the quiz yet – STOP – and go back to step 1 above. Do not look at the answers without first trying the questions.
Various answers are possible. Scientists had no reason to believe that Earth’s surface was changing, so perhaps they never thought to solve that riddle. Because maps encouraged scientists to think about the appearance of Earth, they began to think continental drift was possible.
Wegener had a brilliant idea that the continents drifted, but he could not explain how they drifted. In science, evidence is very important to prove an idea true. Because Wegener could not explain his concept, and others could not observe what he meant, his idea was dismissed easily.
Australia separated from Gondwana completely about 100 million years ago. Monotremes and marsupials probably had not yet evolved, but the only place one can expect to find their fossils is on the Australian continent -- but keep looking!
Although the continent shorelines fit together well, the continental shelves fit together very well. Changes in ocean levels do not influence how the tectonic plates and the continents fit together. Sometimes, explaining Pangaea and other supercontinents by including continental shelves makes good sense.
The supercontinent that forms will have most of Earth’s continents clumped together, but very likely they will come together differently than they have in the past. The large continents probably will stay whole, but Africa is currently being split, and other changes might occur as well.