Download AICE Env Day 5 Evidence of Plate Tectonics Stations

AICE Environmental Management
LAB
Evidence for Plate Tectonics
STATION 1: Article - Seafloor Spreading
The longest chain of mountains in the world is the system of mid-ocean ridges. In the mid-1900s,
scientists mapped the mid-ocean ridges using sonar. Sonar is a device that bounces sound waves off
underwater objects and then records the echoes of these sound waves. The mid-ocean ridges curve
along the sea floor, extending into all of Earth’s oceans. Most of the mountains in the mid-ocean ridges
lie hidden under hundreds of meters of water. A steep-sided valley splits the top of some mid-ocean
ridges. The Earth’s ocean floors move like conveyor belts, carrying the continents along with them, as
they move. This movement begins at a mid-ocean ridge. A ridge forms along a crack in the oceanic
crust. At a mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then
spreads out, pushing older rock to both sides of the ridge. As the molten material cools, it forms a strip
of solid rock in the center of the ridge. Then more molten material splits apart the strip of solid rock that
formed before, pushing it aside. This process, called sea-floor spreading, continually adds new material
to the ocean floor.
Scientists have found strange rocks shaped like pillows in the central valley of mid-ocean ridges. Such
rocks can form only if molten material hardens quickly after erupting under water. The presence of
these rocks supports the theory of sea-floor spreading. More support came when scientists discovered
that the rock that makes up the ocean floor lies in a pattern of magnetized “stripes. The pattern is the
same on both sides of the ridge. These stripes hold a record of reversals in Earth’s magnetic field. The
final proof of sea-floor spreading came from rock samples obtained by drilling into the ocean floor.
Scientists found that the farther from a ridge the rocks were taken, the older they were. The ocean floor
does not just keep spreading. Instead, it sinks beneath deep underwater canyons called deep-ocean
trenches. Where there are trenches, subduction takes place. Subduction is the process by which the
ocean floor sinks beneath a deep-ocean trench and back into the mantle. At deep-ocean trenches,
subduction allows part of the ocean floor to sink back into the mantle, over tens of millions of years.
The processes of subduction and sea-floor spreading can change the size and shape of the oceans.
Because of these processes, the ocean floor is renewed about every 200 million years. The Pacific
Ocean is shrinking. Its many trenches are swallowing more ocean crust than the mid-ocean ridge is
producing. The Atlantic Ocean is expanding. In most places, the oceanic crust of the Atlantic Ocean is
attached to continental crust. As the Atlantic’s floor spreads, the continents along its edges also move.
Directions: Use the figure above to answer the following questions.
1)
2)
3)
4)
What feature of the ocean floor is shown at A?
Describe the process shown occurring at B, and explain what results from this.
What happens to old oceanic crust as new molten material rises from the mantle?
The arrows on the figure show the ocean floor spreading from the ridge. What are two kinds of
evidence scientists have found to support this idea? What process is shown occurring at C,
and why does it occur?
5) Where would you expect to find the “newest” rock on the ocean floor?
STATION 2: Video – Bill Nye Seafloor Spreading
Directions: Use the information provided in the video and your knowledge of Earth Science to
answer the following questions.
Website: http://www.youtube.com/watch?v=GyMLlLxbfa4
1. Until the end of the Second World War, most scientists imagined the ocean floor to look
like what?
2. How many miles long is the mid-Atlantic Ridge?
3. The average seafloor depth is about how deep?
4. The mountains of the mid-Atlantic Ridge sit on average about how much higher than the
surrounding seafloor?
5. True or false: Harry Hess discovered that the age of the seafloor becomes progressively
younger as it moves farther away from the mid-ocean ridge.
6. Hess discovered that molten lava erupted along the mid-ocean ridges, creating new
seafloor. As the new seafloor formed, it pushed old seafloor away from the ridge. What
term did Hess give to this process?
7. The process that recycles the crust of the spreading ocean floor back inside the Earth is
called what?
STATION 3: Data Analysis
Directions: Use the data below to answer the following questions in your composition book.
Seafloor spreading is a process that occurs at mid-ocean ridges, where new oceanic crust is
formed through volcanic activity and then gradually moves away from the ridge. Seafloor
spreading helps explain continental drift in the theory of plate tectonics.
1. Where are the youngest sediments found, compared to the Mid-Atlantic Ridge?
2. Where are the oldest sediments found?
3. Does the data support the theory of sea floor spreading? How?
The diagram below shows an enlargement of the mid-Atlantic ridge and surrounding area in its
position between the continents. Magnetic polarity bands are shown. You will need a ruler and
calculator for question 3.
1.
What would be the age in millions of years of an ocean floor rock found 20 kilometers
west of the ocean ridge?
2.
From point A to point B, what happens to the relative age of the rocks?
A. continuously decrease from A to B
B. continuously increase from A to B
C. decreases from A to the mid-Atlantic ridge and then increases to B
D. increases from A to the mid-Atlantic ridge and then decreases to B
3.
What is the average rate of sea floor movement (centimeters per year or cm/year) from
the mid-Atlantic ridge to point B. Remember that there are 100,000 cm in a km and to
find the rate per year, you will have to multiply the millions of years by 1,000,000. Show
all work.
Rate from mid-Atlantic ridge to point B = ________________________ cm/year
4.
The Hawaiian Islands vary in age from Maui (1 million years old) to Kauai (5 million years
old).
How does the theory of plate tectonics explain the different ages of the Hawaiian
Islands?
STATION 4: The Curious Case of Mesosaurus
Directions: Study the map and read the passage. Then answer the questions that follow on
your composition book.
About 265 million years ago, a reptile called Mesosaurus lived in just a few places on Earth.
This fairly small, lizard-like reptile measured 71 centimeters from its nose to the tip of its tail—
or about two thirds of a meter. Its body was long and flexible, perfect for swimming swiftly
through the water. Mesosaurus was a hunter of small fish and other aquatic animals. Its
webbed feet and long tail worked like powerful paddles as it chased and captured its food. Like
all other reptiles, Mesosaurus breathed air, so it had to return to the surface after hunting
underwater. Freshwater ponds and lakes were its habitat.
In the 1800s, scientists began finding fossils of these ancient reptiles, which had long since
become extinct. These fossils were found in only two regions, southern Africa and the southern
part of South America. The shaded areas on the map show where fossils of Mesosaurus have
been discovered. This distribution is a curious one—only two regions far from each other and
separated by the Atlantic Ocean.
1.
2.
3.
4.
5.
What could explain this distribution?
Describe the kind of environment in which Mesosaurus lived.
Is it likely that Mesosaurus swam back and forth across the Atlantic Ocean? Explain.
What could explain the distribution of Mesosaurus fossils?
Does the case of Mesosaurus support Wegener’s theory of continental drift? Explain why or
why not.
6. Does the case by itself prove the theory? Explain why or why not
STATION 5: The Birth of the Himalayas
Directions: Study the map and read the passage. Then answer the questions that follow on
your composition book.
The greatest challenge for mountain climbers is Mt. Everest, whose peak rises 8,872 meters
above sea level. This is the highest mountain in the world, though many mountains around it
are almost as high. Mt. Everest is in the Himalayas, a series of massive ranges that extends
2,500 kilometers across south Asia north of India. The Himalayas cover all or part of the
countries of Tibet, Nepal, and Bhutan.
A climber on the high slopes of Mt. Everest would probably be surprised to learn that the
region was relatively flat about 40 million years ago. It was then that two continental plates
collided. The plate carrying India had been moving northwards for millions of years. The
oceanic crust in front of it was slowly subducted under the Eurasian plate. But when the two
continents collided, subduction stopped because India could not sink into the mantle. Instead,
it pushed crust upward and downward. The Himalayas were one result. Thus, the Himalayas
are actually pieces of plates broken and lifted up because of the collision. Another result of this
collision was the movement of China eastward, as the movement of India northward pushed
the Eurasian plate in front of it. The collision is still occurring today. In fact, the Himalayas are
growing in elevation at a rate of about 1 centimeter per year.
1.
2.
3.
4.
5.
6.
What are the Himalayas?
What was the area of the Himalayas like 40 million years ago?
How did the movement of plates create the Himalayas?
What else resulted from the collision of those plates?
What type of plate boundary exists today along the Himalayas?
If the Himalayas continue to grow in elevation at their present rate, how tall will Mt.
Everest be in another one million years?
STATION 6: Magnetic Reversals Through the Ages
Directions: Use the graph to answer the questions that follow on your composition book.
On our transit to the Mid-Atlantic ridge, we tow a
magnetometer behind the ship. Shipboard
magnetometers reveal the magnetic polarity of
the rock beneath them. The practice of towing a
magnetometer began during WWII when navy
ships towed magnetometers to search for enemy
submarines. When scientists plotted the points of
normal and reversed polarity on a seafloor map
they made an astonishing discovery: the normal
and reversed magnetic polarity of seafloor
basalts creates a pattern.
 Stripes of normal polarity and reversed polarity
alternate across the ocean bottom
 Stripes form mirror images on either side of the
mid-ocean ridges
 Stripes end abruptly at the edges of continents,
sometimes at a deep sea trench
How often does Earth’s magnetic field reverse itself? The graph below shows the record
geologists have put together for the last 65 million years. As you might know, the last of the
dinosaurs died about 65 million years ago. So you can think of this graph as the record of
Earth’s reversals since the dinosaurs became extinct. In this graph, each dark band represents
a “normal” magnetic field, as it is today. Each light band represents a reversed magnetic field.
1.
2.
3.
4.
5.
Was Earth’s magnetic field “normal” or reversed 65 million years ago?
About how long ago was the last time Earth’s magnetic field reversed?
Can you see any pattern in how often Earth’s magnetic field reverses? Give reasons for
your answer.
How would this history of reversals show itself on the ocean floor?
From this graph, when would you predict the next reversal would occur? Give reasons for
your answer.
STATION 7: A Model for Movement
Directions: Use the model above to answer the following questions.
1. What are you modeling by pushing the strips up through the base?
2. What is being modeled at slits A and B as you push the strips up through the base?
3. This model shows what happens at sea floor spreading centers, such as the mid-Atlantic
Ridge. List at least 2 good points of this model.
4. What are at least 2 reasons why this model is not a good model?
5. Seafloor spreading is continuing today along mid-ocean ridges such as the Mid-Atlantic
Ridge. Predict what effect this will have on the size of the ocean basin
STATION 8: Unit 1 Review
Directions: Use the following cards to review the major topics introduced in Unit 1.
plate tectonics
continental crust
oceanic crust
divergent plate boundary
convergent plate boundary
1. Name and describe the feature of the ocean floor shown at A.
Mid ocean ridge, divergent boundaries the ocean floor has crack that allows molten material to be pushed up
through the crack resulting in the ridge
2. Describe the process shown occurring at B, and explain what results from this.
Sea Floor Spreading, ocean floor is spreading due to divergent boundaries allowing the oldest rock to be pushed
out and the new rock is being formed closest to the crack (forms the ridges)
3. What happens to old oceanic crust as new molten material rises from the mantle?
Old oceanic crust gets pushed out and may get covered with new material if it is close to the crack
4. The arrows on the figure show the ocean floor spreading from the ridge. What are three kinds of evidence
scientists have found to support this idea?
1. Magnetic Strips
2. Rock formation
3. The aging of the rocks
5. What process is shown occurring at C, and why does it occur?
Ocean Trench  Subduction  The oceanic plate slips under the continental plate due to density differences
(Plate movement  convection currents)
6. A device that scientists use to map the ocean floor is _________________.
Sonar device (Map Topography)
7. The feature on the ocean floor at C is called a(n) _________________.
Ocean Trench
8. The process that continually adds new material to the ocean floor is called ______________.
Sea Floor Spreading
9. The process by which the ocean floor sinks into the mantle is called Subduction
10. A chain of underwater mountains along which sea-floor spreading occurs is a Mid ocean Ridge.