Thank you for your purchase!
Please email us with product questions or suggestions.
Support@FlyingColorsScience.com
Holly Edwards Pacheco
Submit Your Email at
www.FlyingColorsScience.com
For a FREE SCIENCE LESSON!
To make a copy of the
Google Slides version
of this activity,
simply click the icon.
Click
HollyHere!
Edwards Pacheco
Continental Drift and Seafloor Spreading
The Earth's structure consists of the solid inner core, liquid outer core, semi-fluid mantle, and solid
crust. The lithosphere, which includes the solid crust and a bit of the upper mantle, is divided into
tectonic plates that float on the semi-fluid asthenosphere below. The movement of these plates is
driven by convection currents within the mantle, caused by uneven heating from Earth's core. As
the warmer, less dense material rises and cooler, denser material sinks, a continuous loop of
movement occurs, leading to the slow motion of tectonic plates. Over millions of years, this
movement of tectonic plates has dramatically changed features on the surface of the Earth.
Continental Drift
Imagine Earth millions
of years ago, when the
continents were not in
their current positions.
Long ago, there was a
gigantic supercontinent known as Pangea. It was like a giant jigsaw puzzle, with all the continents
fitting together. But over time, something extraordinary happened – the continents drifted apart.
The idea of continental drift was first developed by a scientist named Alfred Wegener. He
proposed that Pangea existed hundreds of millions of years ago and that the continents slowly
moved to their present-day locations over millions of years.
Evidence for Continental Drift
Alfred Wegener didn’t know that convection currents in the mantle move Earth’s tectonic plates,
but he did provide several other key types of evidence for continental drift.
• Fit of Continents: The shape of the coastlines of the Americas and Africa fit like a puzzle.
• Rock and Geological Similarities: Rock types and mountain ranges on one continent often
match those on another. For example, the Appalachian Mountains in North America have
similarities to the Caledonian Mountains in Europe.
• Fossil Evidence: Similar fossils of plants and animals have been found on continents that are
now separated by oceans. For
example, fossils of the ancient
reptile Mesosaurus were found
in both South America and Africa.
• Past Climates: Studying rocks,
glacial deposits and fossils can
tell us about the past climate of
an area (paleoclimatic evidence).
Some areas that have cold
climates today show evidence
that they were once warm
climates in ancient times. This
suggests that the land was once
closer to the equator than it is
today. For example, tropical palm
leaf fossils have been found in the
Arctic, which is now very cold.
Holly Edwards Pacheco
©Flying Colors Science
Today, technology has helped scientists to prove continental drift even further. Satellites and GPS
can directly measure the movement of tectonic plates by tracking the positions of continents over
time. By precisely measuring the relative motion of different land masses, scientists can observe
how continents are drifting apart or coming closer together. In fact, these tools have shown that
continents are moving a few centimeters every year!
Seafloor Spreading
But how do the continents move? To understand this, we need to dive beneath the oceans.
Hidden underwater are enormous mountain ranges called mid-ocean ridges. These ridges extend
through the major oceans of the world, including the Mid-Atlantic Ridge in the Atlantic Ocean
and the East Pacific Rise in the Pacific Ocean. At these ridges, two tectonic plates are moving
away from each other due to the slow but powerful convection currents in Earth's mantle.
As the plates move apart, they create a
gap in the ocean floor. Magma, which
is partially molten rock, rises from the
mantle to fill this gap. Once the magma
reaches the seafloor, it cools rapidly and
solidifies to form new oceanic crust.
As more magma emerges and solidifies,
the seafloor moves outward from the
mid-ocean ridge, similar to a conveyor belt. Older parts of each tectonic plate move in opposite
directions on both sides of the mid-ocean ridge, pushing the continents away from each other.
Seafloor spreading is a continuous and slow process. Over millions of years, seafloor spreading
has created vast ocean basins and contributed to the current positions of Earth’s continents.
Holly Edwards Pacheco
Evidence for Seafloor Spreading
Scientists have unearthed a lot of evidence to support the idea that the seafloor is spreading.
• Age of Ocean Floor: Analyzing the age of rocks at the ocean floor has shown that the ocean
floor gets older as you move away from the mid-ocean ridge. The ocean floor is being
created at the ridge and then slowly moving away as new material is added.
• Rock Types: The rocks of the ocean floor are mostly volcanic rocks formed from cooled
magma. So, volcanic activity played a role in creating new ocean floor.
• Magnetic “Stripes” on the Seafloor: When magma solidifies to form new crust, magnetic
minerals in the rock align with Earth's magnetic field.
However, Earth's magnetic field periodically reverses its
polarity. When this happens, newly formed seafloor rocks
will have a different magnetic orientation than the older
seafloor that formed before it. This creates “stripes” of
seafloor. Each stripe of seafloor has a different magnetic
orientation. A new stripe forms each time the Earth reverses
polarity. Rocks of the same age have the same magnetic
orientation. These stripes can be found in the same pattern on
either side of the mid-ocean ridge. The branch of geology that
studies this phenomenon is called paleomagnetism.
Continental drift and seafloor spreading help us understand how Earth's puzzle pieces fit together
and how our planet's surface has changed over time. It's like uncovering the secrets of a
fascinating story that has been unfolding for millions and millions of years.
©Flying Colors Science
Continental Drift and Seafloor Spreading
Name______________________________
Directions: Read the text Continental Drift and Seafloor Spreading and then answer the questions.
1. Use context clues to define the following terms:
Term
Definition
Pangea
paleoclimatic
evidence
mid-ocean ridge
paleomagnetism
2. According to the text, how would Earth’s surface have looked different 200 million years ago?
3. Who proposed the idea of continental drift?
4. What does “continental drift” mean?
Holly Edwards Pacheco
5. Why can’t mid-ocean ridges be seen?
6. What does “seafloor spreading” mean?
7. The steps below summarize how seafloor spreading occurs. Fill in the blanks.
a. As the plates move apart, they create a ______________ in the ____________ _______________.
b. _________________ , which is partially molten rock, rises from the ______________ to fill the gap.
c. Once magma reaches the seafloor, it cools rapidly and _____________________ to form new crust.
d. As more magma solidifies, the seafloor moves ______________________from the mid-ocean ridge.
e. Older parts of each tectonic plate move in _____________________ directions on both sides of the
__________-_________________ _________________ .
f. The _________________________________ are pushed ____________________ from each other.
©Flying Colors Science
8. The ocean floor doesn’t actually have stripes. So, why does the text refer to the ocean floor as
having “stripes?”
9. Use the following grid to summarize the evidence for continental drift. The first one has been
completed for you as an example.
Evidence Type
Explain It
Give a Specific Example
Fit of the
Continents
The coastline shape of continents
match like puzzle pieces.
The coastlines of the Americas
and Africa seem to match.
Fossils
Rock and
Geological
Similarities
Past Climates
Holly Edwards Pacheco
Satellites
and GPS
10. Use the following grid to summarize the evidence for seafloor spreading.
Evidence Type
Explain It
Age of
Ocean Floor
Rock Types
Magnetic
“Stripes” on
the Seafloor
©Flying Colors Science
Continental Drift and Seafloor Spreading
ANSWER KEY
Directions: Read the text Continental Drift and Seafloor Spreading and then answer the questions.
1. Use context clues to define the following terms:
Term
Definition
Pangea
supercontinent that existed hundreds of millions of years ago
paleoclimatic
evidence
studying rocks and glacial deposits to learn about the past climate of an area
mid-ocean ridge
enormous underwater mountain ranges
paleomagnetism
the study of rocks of different ages having different magnetic orientation
2. According to the text, how would Earth’s surface have looked different 200 million years ago?
All the continents would have been joined or very close to each other.
3. Who proposed the idea of continental drift?
Alfred Wegener
4. What does “continental drift” mean?
It means that the continents are moving over long periods of time. They are “drifting.”
Holly Edwards Pacheco
5. Why can’t mid-ocean ridges be seen?
They are under the oceans.
6. What does “seafloor spreading” mean?
New seafloor is being created near mid-ocean ridges, pushing or spreading the older seafloor
in opposite directions.
7. The steps below summarize how seafloor spreading occurs. Fill in the blanks.
a. As the plates move apart, they create a ____gap______ in the ___ocean_____ ____floor_____.
b. _____Magma_____ , which is partially molten rock, rises from the ____mantle___ to fill the gap.
c. Once magma reaches the seafloor, it cools rapidly and ____solidifies_____ to form new crust.
d. As more magma solidifies, the seafloor moves _____outward_________from the mid-ocean ridge.
e. Older parts of each tectonic plate move in _____opposite______ directions on both sides of the
____mid____-____ocean______ _____ridge______ .
f. The ______continents_______ are pushed ______away______ from each other.
©Flying Colors Science
8. The ocean floor doesn’t actually have stripes. So, why does the text refer to the ocean floor as
having “stripes?”
The seafloor is made of rock/crust that was formed at different times. Depending on Earth’s
polarity at the time, new rock had different magnetic orientations. Because new rock gets
pushed farther and farther away from the mid-ocean ridge, this creates bands of rock that have
different magnetic orientations. Students may also explain that the rock has different ages,
creating a banding pattern where older rock is farther away from the mid-ocean ridge and
newer rock is closer to the mid-ocean ridge.
9. Use the following grid to summarize the evidence for continental drift. The first one has been
completed for you as an example.
Evidence Type
Explain It
Give a Specific Example
Fit of the
Continents
The coastline shape of continents
match like puzzle pieces.
The coastlines of the Americas
and Africa seem to match.
Fossils
Similar fossils of plants and animals
have been found on continents that
are now separated by oceans.
Fossils of the ancient reptile
Mesosaurus were found in both
South America and Africa.
Rock and
Geological
Similarities
Rock formations and mountain
ranges on one continent often
match those on another.
The Appalachian Mountains in North
America have similarities to the
Caledonian Mountains in Europe.
Past Climates
Some areas that have cold climates
today show evidence that they were
once warm climates in ancient times.
This suggests that the land was once
closer to the equator than it is today.
Tropical palm leaf fossils have
been found in the Arctic, which
is now very cold.
Satellites and GPS provide direct
measurements of the movement
of tectonic plates by tracking the
positions of continents over time.
Continents are moving a few
centimeters every year.
Satellites
and GPS
Holly Edwards Pacheco
10. Use the following grid to summarize the evidence for seafloor spreading.
Evidence Type
Explain It
Age of
Ocean Floor
The ocean floor gets older as you move away from the mid-ocean ridge,
showing that ocean floor is being created at the ridge and then slowly
moving away as new material is added.
Rock Types
The rocks of the ocean floor are mostly volcanic rocks formed from cooled
magma. So, volcanic activity played a role in creating new ocean floor.
Magnetic
“Stripes” on
the Seafloor
Because Earth’s polarity periodically changes, new rock at the mid-ocean ridge
will have a different magnetic orientation than the older rock that came
before it. This creates magnetic “stripes” on the ocean floor. Rocks of the
same age have the same magnetic orientation. They can be found in the same
pattern on either side of the mid-ocean ridge.
©Flying Colors Science