Laboratory Manual for Introductory Geology 4e

EXERCISE 18.5
Elbow Room? (continued)
Name:
Course:
Section:
Date:
(c) Of that land area, 33% is desert and 24% is mountainous, neither of which is hospitable for human habitation.
Area of uninhabitable deserts and mountains 5 mi 2
(d) The Earth’s habitable land surface 5 land area 2 (desert area 1 mountain area) 5 mi 2
STEP 3: How much area is available for each person on the Earth?
(e) There are approximately 7.4 billion people on the Earth (7,400,000,000). How much living space is there for each
person, in square miles? mi 2
(f) To better understand what this number means, convert square miles to square feet (ft 2 ), remembering that 1
square mile 5 5,280 ft 3 5,280 ft. Each person therefore can claim
ft 2 —but remember that this figure
does not consider farms, highways, and so forth.
(g) Under the moderate fertility scenario shown in Figure 18.13, the Earth will host 10 billion humans by around 2050.
How much living space will each person have in 2050?
ft 2 . Explain your reasoning.
18.3 Humans as Agents of Environmental
Change and Extinctions
Are humans contributing to the increased rate of extinction? We saw evidence earlier
in this chapter that humans are changing the atmosphere, cryosphere, and hydrosphere,
and those changes cannot help but affect the biosphere. But, in addition
to our role in climate change, there are four ways in which humans more directly
contribute to extinctions, which, when added to our impact on climate change,
have a cumulative effect that is potentially as devastating as any of the natural causes
of mass extinctions in the geologic past.
1. Humans are very effective predators. Hunting is the most direct way in which
humans have caused some species to become extinct. Perhaps the two most
notable recent examples were the extinctions of the dodo in the 17th century
and the passenger pigeon in the 20th century (FIG. 18.14). The dodo was a large
flightless bird that had no predators and, therefore, had no defense against
the sailors who began hunting them for meat. Passenger pigeons used to be so
plentiful that enormous flocks of them once blackened the sky for hours at a
time, but they were easy prey for hunters with shotguns, and so they too were
decimated and driven to extinction.
Other notable species that nearly suffered the same fate include the snowy egret
(hunted for its feathers), the gray wolf, the whooping crane, and the American
bison, but aggressive conservation measures have brought these animals back
from the edge of extinction. However, their populations are only a tiny fraction
of what they were two hundred years ago. Similar measures have been taken
18.3 HUMANS AS AGENTS OF ENVIRONMENTAL CHANGE AND EXTINCTIONS
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