Section 8.2 (Assigned:____________Due:____________)
____Read pages 161 – 165 in your text.
____Complete the study session.
____Add the 6 vocabulary words and definitions.
____Draw Figure 8.5: A convection cell in the lower mantle
____Use the illustrations on page 165 to draw, label and indicate the age of each of the
Hawaiian Islands.
____Answer the True/False questions about Section 8.2
Study Session:
I.
II.
III.
IV.
Undersea mountains discovered
A. American geophysicist and Naval officer Harry Hess mapped large areas
____________________________. His work helped develop the theory of
____________________.
B. Huge mountain ranges called ______________________________ formed a
_________________________down the centers of the ocean floors.
The sea-floor spreading hypothesis
A. Hess believed that the continents moved along as part of the growing sea floor
and called his hypothesis ______________________________.
B. Patterns in rocks called _________________________ were read by scientists as
strong evidence to explain sea-floor spreading.
C. Scientists determined that on either side of a mid-ocean range the oldest rocks
were _____________________________.
D. New ocean floor is formed at ______________ridges and the new floor
_________________________from the ridge as time passes.
Moving pieces of the lithosphere
A. Scientists soon realized that large pieces of Earth’s surface moved
________________________________________.
B. These rafts are pieces of lithosphere called ___________________________.
C. There are 2 kinds of lithospheric plates: _____________________and
___________________________.
What drives lithospheric plates?
A. _______________________________in Earth’s lower mantle drive the
lithospheric plates on the surface.
B. Rocks of the lower mantle are hot enough so they ______________________.
C. The _____________heats the rock of the lower mantle which expands and
________________________________.
D. The lower mantle rock material rises toward ________________________.
V.
E. The far edge of a lithospheric plate cools, becomes more dense, and may
_________________________________________________________.
F. The now-cool subducting plate enters the ___________________.
G. Cooling makes the nearby material denser and it
___________________________________________________.
Hot spots and island chains
A. Mid-ocean ridges form when __________________________________
________________________________________________________.
B. Sometimes a single hot rising plume, called a _____________________ causes a
______________________________in the plate above it.
C. If the eruption is strong and lasts long enough, a _____________________may
be formed.
D. After the island forms, the movement of the plate ______________________
_______________________________________________________.
E. Without the heat from the mantle plume underneath, the volcano that formed
the island becomes __________________.
F. A new volcano begins to form on the part of the plate that is now
____________________________________________.
G. This process repeats over and over and forms __________________________.
Vocabulary words:
1. _____________________________:
________________________________________________________________________
________________________________________________________________________
2. _____________________________:
________________________________________________________________________
________________________________________________________________________
3. _____________________________:
________________________________________________________________________
________________________________________________________________________
4. _____________________________:
________________________________________________________________________
________________________________________________________________________
5. _____________________________:
________________________________________________________________________
________________________________________________________________________
6. _____________________________:
________________________________________________________________________
________________________________________________________________________
True/False:
____1. Large areas of the ocean floor were mapped for the first time during World War II.
____2. Harry Hess wondered if it was possible that new ocean floor was created at the midocean ranges.
____3. Hess believed that Wegener’s theory of continental drift was totally wrong.
____4. For many years, scientists had thought that the continents were fixed in place.
____5. Scientists used the magnetic patterns in rocks to determine that the oldest rocks were
furthest from a mid-ocean ridge.
____6. New ocean floor is formed at mid-ocean ridges.
____7. The new floor moves away from the ridge as time passes.
____8. Scientists realized that large pieces of Earth’s surface moved about like rafts on a river.
____9. These rafts are pieces of the core.
____10. Plate tectonics is the study of lithospheric plates.
____11. Oceanic plates form the floor of the ocean, are thin, and are made of dense basalt.
____12. Continental plates are thick and made of less-dense granite.
____13. Often the lithosphere is a mix of both kinds of plates.
____14. Convection cells in Earth’s lower mantle drive the lithospheric plates on the surface.
____15. The far edge of a lithospheric plate is much older than the edge close to the mid-ocean
ridge that formed it.
____16. Mid-ocean ridges form when rising hot mantle rocks separate the plate above it.
____17. Sometimes a mantle plume causes a volcanic eruption in the plate above it.
____18. The first island formed in an island chain is made of old dormant volcanoes.
____19. The most recent island in the string probably has active volcanoes.
____20. The Hawaiian Islands are a good example of an island chain formed by a mantle plume
hot spot.
Figure 8.5 “A convection cell in the lower mantle”
The Hawaiian Islands