Download Guided Reading on Sections 23.3 and 23.4

Name:
Date:
Period:
Guided Reading:
Continental Drift &
Plate Tectonics
Start on page 571, §23.3 “The Theory of Continental Drift” and answer the following
questions as you read:
1. Scientists of the early 20th century believed that _____________ and
___________________ were geographically fixed.
2. They regarded the surface of the planet as a static _________ spread over a
molten, gradually cooling _______________. They believed that the cooling of
the planet resulted in its ___________________, which caused the outer skin to
contort and wrinkle into ____________________ and ________________.
3. Many people had noticed, however, that the eastern shorelines of ___________
__________________ and the western shoreline of ______________ seemed to
fit together like a jigsaw puzzle (Figure 23.9).
4. One Earth scientist who took this observation seriously was ____________
_________________, who saw the Earth as a dynamic planet with the
___________________ in constant motion.
5. He believed that all the continents had once been joined together in one great
supercontinent he called _______________, meaning “_______ __________.”
6. His hypothesis was that _____________ had fractured into a number of pieces,
and that South America and ______________ had indeed once been joined
together as part of a larger land mass.
7. He proposed that the geological boundary of each continent lay not at its
________________ but at the edge of its __________________ ___________
(the gently sloping platform between the shoreline and the steep slope that leads
to the deep ocean floor).
8. When Wegener fit Africa and South America together along their continental
shelves, the fit was even better than it was at the shorelines (Figure 23.10).
Furthermore, ___________ on different continents that are brought into
juxtaposition when the __________________ ____________ are matched up are
virtually identical.
9. In addition, many of the _________________ _____________ in Africa and
South America show strong evidence of a previous connection.
10. Similarly, _____________ of identical land-dwelling animals are found in South
America and Africa but nowhere else. And fossils of identical ___________ are
found in South America, India, Australia, and Antarctica.
11. One of the first key discoveries in support of _________________ ___________
came about through studies of the Earth’s magnetic field.
12. The 1950’s were a time of extensive and detailed mapping of ocean floors.
Topographic features revealed huge ________________ ranges running down the
middle of the Atlantic, Pacific, and Indian Oceans; a major rift __________ along
each crest; and deep ocean ______________ near some of the continental
landmasses, particularly around the edges of the Pacific (Figure 23.12).
13. So, some of the deepest parts of the ocean are actually near some of the
________________, and out in the middle of the oceans the water is relatively
________________ because of the underwater mountains.
14. With this new information, H. H. Hess, an American geologist, presented the
hypothesis of ______________ __________________.
15. Hess proposed that the seafloor is not permanent but is constantly being
_______________. He theorized that the ocean ridges are located above
upwelling convection cells in the _______________.
16. As the rising material from the mantle oozes upward, new ___________________
is formed. The old lithosphere is simultaneously destroyed in the deep ocean
_____________ near the edges of __________________.
17. Thus in a conveyor belt fashion new lithosphere forms at a spreading center, and
older lithosphere is pushed from the ______________ ___________ to be
eventually recycled back into the ______________ at a deep ocean trench (Figure
23.13).
18. The theory of _______________ __________________ provided a mechanism
for continental drift.
Continue to page 574, §23.4 “The Theory of Plate Tectonics” and answer the following
questions as you read:
1. The ____________ ____ _______________ _________________ holds that
the Earth’s outer shell, the ____________________, is divided into eight
relatively large plates and a number of smaller ones (Figure 23.15).
2. All major interactions between plates are manifested along __________
_________________.
3. Convection in the Earth’s _____________ causes the overlying lithospheric
plates to be in slow but constant _______________.
4. Rocks subjected to stress begin to deform into intricate and broad __________,
and if enough stress is applied, rocks break and then move along ____________.
5. Folds occur when a rock is subjected to compressive stress and it begins to
______________ and ___________.
6. Faults occur when compressional stress overcomes the strength of rock, the rock
fractures into ________ parts. If one part then moves relative to the other part,
the fracture is called a ______________.
7. Refer to Table 23.1, which of the locations listed experienced the largest
earthquake ever recorded? ______________________________
8. Define divergent boundaries:
9. Define rifts or rift valleys:
10. Define convergent boundaries:
11. Define transform-fault boundaries: