Download Seafloor Spreading Math Connections

Seafloor Spreading (B)
The History of Planet Earth
Seafloor Spreading
In the early 20th century, Alfred Wegener developed his theory of continental drift, explaining that
the continents on Earth move and historically were in different positions from their current
locations today. He used evidence from fossil findings, geologic formations, and coastal outlines
of the continents to support his theory. In the 1960s, scientific discoveries about seafloor
spreading, combined with the theory of continental drift, led to the theory of plate tectonics.
In 1962, Harry Hess and a naval team were mapping the Atlantic ocean floor for the United
States Navy when they discovered the Mid-Atlantic Ridge (MAR). His discovery of the newly
formed ocean floor was the evidence Wegener was searching for in 1912. Hess explained that
the MAR is the result of divergent tectonic plates, which explains how the ocean floor is renewed
and why continental plates appear to be younger than oceanic plates.
Refer to the map, “Spreading at Mid-Ocean Ridge Between African and North America Plates,”
on Page 3 to answer questions 1 and 2.
1. What is the map scale?
2. Using the map scale, calculate the distance between the following locations on the map.
Distance in kilometers = Distance in cm x Map scale in cm/km
Locations
Distance
Point A and Point B
Point B and Point C
Point A and Point C
North America and Africa
(measure the distance between dots)
The map highlights the mid-ocean ridge between the North American Plate and the African Plate.
As the North American and African plates move away from each other, magma rises up between
the two plates. New oceanic crust forms when the magma cools and the plates continue to move
apart. The lines on the map represent time in a unit of millions of years. The newest crust is
found at 0, the mid-ocean ridge, and the crust gets older as you move out on either side of the
ridge. By selecting a point on the crust, you can use its age and its distance from the mid-ocean
ridge to calculate the average speed at which the plate is moving away from the mid-ocean
ridge. Use the following formula to calculate this plate speed:
Average Plate Speed in cm/yr = distance in cm
time in years
1
Seafloor Spreading (B)
The History of Planet Earth
Use the information from the previous page to answer questions 3–6.
3. Calculate the average speed (cm/yr) of the North American plate for the last 156 million
years. For the total distance, measure from Point A to Point B. (Remember: 1 km = 100,000
cm)
4. Calculate the average speed (cm/yr) of the African plate for the last 156 million years. For the
total distance, measure from Point B to Point C.
5. Calculate the average spreading rate between the North American and African plates using
the formula:
Average Spreading Rate (cm/yr) = total distance (cm) / total time (yr)
For the total distance, measure from point A to point C.
6. Use the average spreading rate you calculated in question 5 to calculate the amount of
spreading that has occurred between North America and Africa during your lifetime.
7. If the average spreading rate stays the same, how much will the distance between Africa and
North America increase by the year 3025?
8. Calculate the average spreading rate between the two plates during the last 20 million years.
9. Calculate the average spreading rate between the two plates during the last 35 million years.
Does the average spreading rate stay constant over time?
2
North
America
A
118
84
B
55 35
20
Mid-Ocean Ridge
North American Plate
156
55
84
African Plate
0
20 35
C
156
Map Scale
1cm = 500 km
118
Age of Crust in Millions of Years
Spreading at Mid-Ocean Ridge between
African and North American Plates
Afric
a
Seafloor Spreading (B)
The History of Planet Earth
3