Download OBJECTIVES: Students will gain an understanding of how

Honors Earth/Space Science
Name _________________________________
SEAFLOOR SPREADING IN THE ATLANTIC OCEAN
Period _______ Date ______________
OBJECTIVES: Students will…
 Observe and analyze the ages of seafloor rocks.
 Identify the Mid-Atlantic Spreading Ridge (MAR).
 Use map scales to determine the distance between the MAR and adjacent coastlines.
 Determine rates of sea floor spreading between two tectonic plates.
MODEL 1: Strip map of a portion of the North Atlantic region between North America and Africa. The
coastlines are given a heavy line and the continental shelf edge is a lighter outline. Seafloor basalt ages
are indicated in millions of years. Basalt is the type of rock that is found in the ocean floor (crust). It is
igneous.
The numbers indicate the age of the
sea floor rocks in millions of years.
MODEL 2: Below is a profile (side-view) of the elevation of the seafloor between Points A and B with the 0year old basalts indicated. These new basalts are associated with active submarine volcanoes.
Point A
Point B
Age = 0 years
USING OBSERVATIONS TO GENERATE A HYPOTHESIS…
1. What continents are shown in Model 1?
2. List three observations of the distribution of basalt ages:
3. Develop a statement describing the distribution of basalt ages:
4. List three observations about the elevation of the seafloor:
5. Develop a statement describing the elevation of the seafloor:
Scientists refer to the Mid-Atlantic submarine mountainous region as the Mid-Atlantic Ridge. The Theory
of Seafloor Spreading states that seafloor spreading is a process that occurs at mid-ocean ridges, where
new ocean crust is formed through volcanic activity and then gradually moves away from the ridge.
Seafloor spreading helps explain the theory of continental drift in the theory of plate tectonics. When
oceanic plates diverge, tensional stress causes fractures to occur in the lithosphere. Basaltic magma
rises up the fractures and cools on the ocean floor to form new sea floor. Older rocks will be found further
away from the spreading zone while younger rocks will be found nearer to the spreading zone.
USING OBSERVATIONS TO MAKE CALCULATIONS…
6. Creating a scale for the map in Model 1.
a. Using Model 2, determine the actual distance between Points A and B. Record the value
in kilometers:
b. Use a ruler to draw a line between Points A and B on the map in Model 1. Measure and
record that distance in centimeters:
c.
Determine the scale of the map by simplifying the ratio of the map distance/actual
distance (1 cm = ________km):
7. Find the rate of movement between the spreading ridge and Point A.
a. Using the scale of the map that you determined in question 6, find and record the
distance between Point A and the mid-ocean ridge in km:
b. Record the age of the seafloor basalts nearest to Point A:
c.
Determine the rate or velocity that Point A moved away from the Mid-Atlantic Ridge in
i. ____________________km per MY
ii. ____________________cm per year
This rate is actually considered the “half-rate” of seafloor spreading because Africa is also moving away
from the ridge. The actual rate of seafloor spreading is determined by calculating the rates on both sides
of the ridge and adding them together.
8. Find the rate of movement between the spreading ridge and Point B.
a. Using the scale of the map that you determined in question 8, find and record the
distance between Point B and the mid-ocean ridge in km:
b. Record the age of the seafloor basalts nearest to Point B:
c.
Determine the rate or velocity that Point B moved away from the Mid-Atlantic Ridge in
i. ____________________km per MY
ii. ____________________cm per year
9. Analyze and compare your answers in questions 7 and 8. Write a statement about how the rates
are similar and how they are different:
10. How much has the distance (in cm) between North America and Africa increased since you were
born?
11. How much does the distance (in meters) increase during the average lifetime of an American
(~82 years)?
12. How much closer (in meters) were these two continents when Columbus made his voyages (in
1492)?