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See also: Human activity and biodiversity 92–95 ■ Biodiversity hotspots 96–97
■ Biomes 206–209 ■ Deforestation 254–259 ■ Environmental ethics 306–307John Muir
Born in Scotland in 1838, John
Muir developed a passion for
nature as a boy. He moved
with his family to Wisconsin
at the age of 11. In 1867, he
had an accident in which he
lost his sight temporarily, after
which he “saw the world in a
new light.” An accomplished
botanist, geologist, and
glaciologist, Muir visited the
Yosemite Valley in California
in 1868, and later determined
to preserve it from the scourge
of domestic sheep (which he
called “hoofed locusts”). In
1903, Muir took President
Theodore Roosevelt on a
guided tour through the
Yosemite Valley, and their
three-day trip inspired
Roosevelt to create the US
Forestry Service and, in
1916, to form the National
Conservation Commission.
Until his death in 1914, Muir
continued to advocate for the
conservation of land such as
Mount Rainier, which became
a National Park in 1899.fires. Hurricanes and rivers in flood
can wreak havoc. Storm surges may
produce inundations of the sea,
turning freshwater wetlands saline.
About 65 million years ago, the
Chicxulub meteor impact in Mexico
produced a dust cloud so great that
it stopped sunlight from reaching
Earth’s surface. Plants struggled
to photosynthesize, and many
animals, including the dinosaurs,
became extinct.
Nor is human influence an
exclusively recent issue. Throughout
history, people have modified their
environment. Deforestation, for
example, is not a new problem. In
Europe, the clearance of forests for
agriculture and construction began
thousands of years ago, and a similar
pattern followed in North America.
However, the impact of modern-
day humans on the environment is
unprecedented. In the past 200
years, the human population has
exploded. This has fueled the rapidgrowth of cities, the development
of large-scale industry based on the
extraction of fossil fuels and raw
materials, a growing agricultural
demand to feed more people, and
conflict and war. All these have
taken their toll on the natural world.Fragile ecoregions
A concept that is now often used
to identify the major habitat types
on Earth is that of the ecoregion—
smaller than a biome, with a more
detailed gauge of biodiversity.
Ecoregions are defined as large
units of land or water containing
a geographically distinct mix of
species, natural communities, and
environmental conditions. Some
examples include deserts, tropical ❯❯THE HUMAN FACTOR
Key works1874 Studies in the Sierra
1901 Our National Parks
1911 My First Summer
in the SierraYosemite National Park was created
in 1890, thanks to the efforts of John
Muir. The park is famed for its glaciers,
waterfalls, and granite rock formations,
such as the El Capitan monolith.US_236-239_Endangered_habitats.indd 237 12/11/18 6:25 PM