Geography Reference
In-Depth Information
Key Questions
For Chapter 13
1.
How has Earth's environment changed over time?
2 .
How have humans altered Earth's environment?
3.
What are the major factors contributing to environmental change today?
4.
What is the international response to climate change?
had relatively limited effects on a global scale. Over the
last 500 years, however, both the rate and the scale at
which humans modify Earth have increased dramatically.
Particularly during the last half-century, every place on
earth has been transformed, either directly or indirectly,
by humans.
During our brief presence on this planet, humans
have had a powerful impact on environments ranging
from rainforests to tundras. Long before we became tech-
nologically profi cient we exterminated wildlife by the mil-
lions and burned grasslands and forests by the hundreds
of thousands of square miles. The twentieth-century
surge in the size of the human population, combined with
a rapid escalation in consumption, magnifi es human-
ity's impact on Earth in unprecedented ways. Although
Homo sapiens
have not dominated this world long, we have
had enough of an impact that atmospheric chemist Paul
Crutzen defi ned a new geologic epoch called the
anthro-
pocene
to acknowledge the incredible role humans play
in shaping Earth's environment.
HOW HAS EARTH'S ENVIRONMENT
CHANGED OVER TIME?
Environmental variation, spatial as well as temporal,
is one of Earth's crucial characteristics. Temperatures rise
and fall, precipitation waxes and wanes. Forests fl ourish
and wither, deserts expand and contract. Humanity has
evolved during a series of alternatively warm and cold
phases of an Ice Age that is still in progress. But today
humanity itself is part of the process.
Modern
Homo sapiens
emerged less than 200,000
years ago (and possibly not much more than 100,000 years
ago). Humans altered their environment from the begin-
ning by setting fi res to kill herds of reindeer and bison,
or hunting entire species of large mammals to extinc-
tion. The Maori, who arrived in New Zealand not much
more than 1000 years ago, greatly altered native species
of animals and plants long before the advent of modern
technology. Elsewhere in the Pacifi c realm, Polynesians
reduced forest cover to brush and, with their penchant for
wearing bird-feather robes, exterminated more than 80
percent of the regional bird species by the time the fi rst
Europeans arrived. Europeans ravaged species ranging
from Galapagos turtles to Antarctic seals. European fash-
ions had a disastrous impact on African species ranging
from snakes to leopards. Traditional as well as modern
societies have had devastating impacts on their ecosys-
tems (ecological units consisting of self-regulating asso-
ciations of living and nonliving natural elements) as well
as on ecosystems into which they migrated.
Human alteration of environment continues in
many forms today. For the fi rst time in history, how-
ever, the combined impact of humanity's destructive and
exploitative actions is capable of producing environmen-
tal changes at the global scale. Consider for a moment
the history of human life on Earth. Early human societies
had relatively small populations, and their impacts on the
physical environment were limited in both duration and
intensity. With the development of agrarian and prein-
dustrial societies, human alterations of the physical envi-
ronment increased, yet the effects of these early activities
were still limited in scale. Even the onset of urbaniza-
tion and the development of urban centers, which con-
centrated large numbers of people in particular places,
Tectonic Plates
How representative is the short-term present of the long-
term past? Over the past century, geographers and other
scientists have been engaged in a joint mission to recon-
struct our planet's history on the basis of current evi-
dence. One of them, the climatologist-geographer Alfred
Wegener, used his spatial view of the world to make a key
contribution. Viewing the i
ncreasingly accurate maps of
the opposite coastlines of the North and South Atlantic
oceans, he proposed a hypothesis that would account for
the close “fi t” of the shapes of the facing continents, which,
he argued, would be unlikely to be a matter of chance. His
continental drift hypothesis required the preexistence of a
supercontinent, which he called
Pangaea
, that broke apart
into the fragments we now know as Africa, the Americas,
Eurasia, and Australia (Fig. 13.3).
Wegener's hypothesis
engendered the later theory of plate tectonics and crustal
spreading, and scientists now know that Pangaea and its
fragmentation were only the latest episodes in a cycle of
continental coalescence and spli
ntering that spans billions
of years. This latest Pangaean breakup, however, began
only 180 million years ago and continues to this day.
