Page 72 - Laboratory Manual in Physical Geology

A CTIVIT Y 2.2 Is Plate Tectonics Caused by a Change in Earth’s Size?

Name: ______________________________________ Course/Section: ______________________ Date: ____________

A. Recall that geoscientists have historically tried to What kind of faulting would
understand the cause of oceans, mountains, and global you most expect to find in
the lithosphere if:
tectonics by questioning if Earth could be shrinking or
expanding in size. This question can be evaluated by
1. Earth is expanding?
studying Earth’s natural forces and faults in relation to
those that you might predict to occur if the size of Earth

were changing. Analyze FIGURE 2.4 to see how three

kinds of faults are caused by three kinds of stress (applied
force). To the right of this diagram, predict what kind Original
size of 2. Earth is contracting?
of faulting you would mostly expect to find in Earth’s Earth
lithosphere if Earth were expanding or contracting
(shrinking).

B. Refer to FIGURES 2.2 and 2.4 . Fill in the table below to indicate what kind of stress and faulting characterizes each kind of

plate boundary.
Plate Boundary Type Main Stress (applied force) Main Fault Type

Divergent

Convergent

Transform

C. Refer to FIGURE 2.5 , a map showing the distribution of Earth’s lithospheric plates and three main kinds of plate boundaries:

divergent (red), convergent (hachured), and transform (dashed). Also note in FIGURE 2.2 that there are two kinds of divergent
boundaries (continental rifts, mid-ocean ridges) and three kinds of convergent boundaries (ocean-ocean, ocean-continent, and
continent-continent).

1. Geologist Peter Bird conducted a classical study of Earth’s lithospheric plates and plate boundaries in 2003. He found that
the lithosphere is actually broken into 52 plates, many of which are too small to see on a world map. So the typical global
map of about 13 main plates shown in FIGURE 2.5 and most textbooks is quite generalized. He also identified the total

combined lengths of all of the different kinds of plate boundaries, as summarized in the two left-hand columns of the table
on the back of this page. Complete the two right-hand columns of the table.

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