SeaFloorSpreadingHW-1
pdf
keyboard_arrow_up
School
California State University, Long Beach *
*We aren’t endorsed by this school
Course
100
Subject
Geology
Date
Dec 6, 2023
Type
Pages
3
Uploaded by BrigadierRaven3605
Student Investigation
How Fast is the
Ocean Floor Moving?
•
77
•
79
Pacific Ocean
140°w
120°w
DATE
500
400
300
200
,oo
20° s
100°w
80°W
Figure 1. Site locations of Leg 9 deep sea drilling
cores. (Modified from Hays, J.D., and others, 1970,
p. 12, with permission .)
INTRODUCTION
Earth scientists believe that the continents of Africa and South America
were once joined together. What is the evidence for this hypothesis? If it is true,
how long has it taken for these two continents to break apart and move to where
they are now?
One way to answer these questions is to study samples of sediment taken
from the ocean floor.
Sediment
is loose rock, mineral debris, and plant and an-
imal shells which have settled out of the water. In these activities you will use
sediment data, like scientists do, to determine how fast the ocean floor is
moving.
The deep sea sediments were obtained by the
Glomar Challenger.
The
Glomar Challenger
is a specially designed drilling ship that can take samples
of sediment and rock from the floor of deep ocean basins. It recovers both sed-
iment and rock cores. A core is a cylinder of sediment or rock obtained by using
a hollow drill. In many cases, scientists must drill through hundreds of meters
of sediment before reaching the solid igneous rock of the ocean floor. This ig-
neous rock forms by cooling and hardening of molten rock material. It is the
“floor” upon which the sediments settle.
OBJECTIVES
After you have completed these activities, you should be able to:
1. Make and interpret graphs which show the relationship between the thick-
ness of a sediment sample and its distance from an
oceanic ridge
.
2. Make and interpret graphs which show the relationship between the age of
deep sea sediments and their distance to an oceanic ridge.
3. Form hypotheses about sea-floor movement based on
data from sediment cores.
4. Calculate the rate of movement of the ocean floor from
data on sediment thicknesses, ages of sediment, and loca-
tions of the drill sites.
PART A: What can we learn from deep sea sedi-
ments?
The data you will be using in this activity are based on
measurements from sediment cores. The
Glomar Chal-
lenger
drilled these sediment cores near the
East Pacific
Rise
. The East Pacific Rise is part of a 64,000 km-long
oceanic ridge system. Oceanic ridges are thought to be places where the process of sea-floor spreading
(which results in breakup and separation of continents) takes place. Figure 1 (previous page) is a map
showing where the cores were drilled.
1.
Based on what you’ve read in the book, what we’ve discussed in class, and common sense, you
would expect that the sediment would get _______________ (thicker or thinner) as you go away from
the axis of the East Pacific Rise.
2.
To the right is a profile of the
bedrock
(igneous rock)
of the ocean floor on each side of the East Pacific Rise.
Sketch in the sediment, showing how sediment thickness
changes in both directions away from the middle of the
East Pacific Rise. Use your answer to the previous ques-
tion as a guide.
3.
Using the sediment thickness data from Table 1, complete the graph on the next page. Plot the dis-
tance to the East Pacific Rise along the horizontal axis. Plot the sediment thickness along the vertical
axis.
4.
Does your graph of distance versus sediment thickness lend support to the theory of
plate tectonics
?
Does it show what you expected (questions 1 & 2)? __________ (yes or no)
5. Briefly
explain
what the graph means.
6.
Explain
how the graph supports the theory of plate tectonics.
Table 1:
Glomar Challenger
deep sea cores, Leg 9.
(Modified from Hayes, J.D., and others, 1970, p. 12, with permission.)
Drill site number
(and location)
Distance from the middle of
the East Pacific Rise
Sediment thickness
Age of sediment at the
bottom (million years)
77 (west of EPR)
3,359 km
481 m
36
79 (west of EPR)
2,086 km
414 m
21.5
81 (west of EPR)
1,280 km
409 m
14.5
82 (west of EPR)
549 km
214 m
9.5
Approximate ridge axis
0 km
none recovered
0
83 (east of EPR)
797 km
241 m
10.5
Graph for question 3:
500
400
Bottom sediment age, in millions of years
Sediment thickness, in meters
300
200
100
0
0
800
1600
2400
3200
4000
Distance to the EPR from either side, in kilometers
7. Another graph. For each drilling
50
site number, plot the distance to
the ridge center along the horizon-
tal axis. Plot the bottom sediment
age along the vertical axis.
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-
-
-
-
-
-
-
-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
40
30
20
10
8.
The graph shows that bottom
sediment age ______________
(increases or decreases) as the dis-
tance from the ridge axis increas-
es.
9.
Explain
how this graph (the
graph for question 7) supports the
theory of plate tectonics.
(2 points)
0
0
800
1600
2400
3200
4000
Distance to the EPR from either side, in kilometers
Your preview ends here
Eager to read complete document? Join bartleby learn and gain access to the full version
- Access to all documents
- Unlimited textbook solutions
- 24/7 expert homework help