|
Life on Earth exists in the biosphere—a life-supporting zone that extends from the deep-sea vents in
the ocean to an altitude of about ten miles.
The biosphere includes the earth's atmosphere—the layer of gas that surrounds our planet like a blanket.
The air we breathe is found in the first layer of the atmosphere, called the troposphere. Above the
troposphere is the stratosphere, which includes a layer of ozone that protects Earth from harmful radiation.
Although it is widely debated, many scientists believe gases in the stratosphere have thickened, trapping
warm air in the atmosphere. The so-called greenhouse gases that trap warm air near the earth include CFCs
(chlorofluorocarbons)—manufactured gases first developed in the 1920s. CFCs are used in cleaning
materials, refrigerators, and car air conditioners. The release of CFCs into the atmosphere has been
connected to a thinning of the ozone layer around much of the earth and the opening of a hole in the
ozone layer over Antarctica. Scientists say the ozone hole poses a serious threat to the survival of
human beings and to plant and animal life.
Ecologists divide the biosphere into biomes. These geographical areas have unique characteristics,
climates, and vegetation patterns. Tropical rain forests, deserts, grasslands, tundra, boreal forests,
and deciduous forests are all biomes. The marine ecosystem is also a biome. Every ecosystem has nonliving
physical factors, such as sunlight, water, and minerals, in addition to living factors, like plants and animals.
A balancing act between producers, consumers, and decomposers takes place within each ecosystem,
forming food chains that contribute to food webs and ultimately to the web of life. Everything in
these ecosystems is interconnected and interdependent.
People's Place in Nature
Population growth has caused a huge demand for food and shelter—basic human needs. Deforestation,
the process of clearing forests, provides people with lumber to build homes and land for farming.
Deforestation also has negative consequences, including loss of plant and animal habitats and the
biodiversity necessary to reproduce healthy species. Industrialization has provided a better way
of life for many people, but the environment has paid a heavy price.
|
 |
 |
We share the world with plants and animals, and through the help of zoos, aquariums,
and other organizations, concerned people are working to protect endangered species and their
habitats. We want to be sure that the thrill of a whale's leap from the water, the joy of a
mother gorilla with her baby, or the excitement of condors returning to the wild can be
enjoyed by future generations.
|
|
Scientists have been at the forefront of efforts to alert people to the dangers of
environmental devastation. Much of the focus has been on the need to preserve natural habitats
in the world's shrinking rain forests and to make responsible use of scarce resources.
Many have also urged greater emphasis on fuel-efficient technologies. Hybrid car
engines and fuel cells hold enormous potential for reducing greenhouse gas emissions that
threaten our delicate biosphere.
