called photosynthesis. Forest trees also
help to protect soil from erosion. They
block the forces of wind and water that
wear away the land. In addition, forests
offer a peaceful place for hiking, camping,
bird-watching, and exploring
nature.
Protecting Forests
For thousands of years people have been
cutting down forests for wood and to
make room for farms and cities. Now
many of the world’s forests are in danger
of disappearing. Many people work to
protect forests.
Forestry is the science of managing
forests. People who work in forestry
study the life cycles of trees and other
forest plants. Foresters usually have a
college degree in forest sciences. They
work to prevent the spread of tree
diseases, keep trees safe from harmful
insects, and control forest fires. Many
professional foresters work for the
government.
To save forests many governments also
create national forests, state parks, and
wilderness preserves. In these places forests
are left in their natural state for
people to enjoy. Sequoia National Park
in California was created in 1890 to
protect groves of giant sequoia trees.
#More to explore
Erosion • National Parks
• Photosynthesis • Rain Forest • Tree
A woman walks through a tropical forest in Seychelles, an island country in the Indian
Ocean. Hiking is a popular activity in many forests.
54 Forest BRITANNICA STUDENT ENCYCLOPEDIA
Fossil
Fossils are the remains or traces of plants
and animals that lived long ago. Fossils
give scientists clues about the past. For
this reason, fossils are important to paleontology,
or the study of prehistoric life.
Most fossils are found in earth that once
lay underwater. They usually formed
from the hard parts—such as shells or
bones—of living things. After a living
thing died, it sank to the bottom of the
sea. Layers of earth and the remains of
other living things built up on top of it.
Over time, these layers turned into rock.
Eventually, part or all of the living
thing’s hard parts also turned into rock.
The fossil is the shape of these hard
parts in the rock.
Other fossils are imprints on soft material
that later hardened into rock. For
example, scientists have found dinosaur
footprints in rock that formed from
mud. Many plants left leaf prints, too.
Another kind of fossil can form after a
small insect or a piece of a plant gets
trapped in resin. (Resin is a sticky substance
made by pine and fir trees.)
When the resin hardens into a rocklike
material called amber, the object inside
is preserved.
#More to explore
Amber • Paleontology • Prehistoric Life
• Rock
Fossil Fuel
All the machines of modern life require
energy to make them run. About 90
percent of that energy comes from burning
fossil fuels. Fossil fuels include petroleum
(oil), coal, and natural gas. These
materials are called fossil fuels because,
like fossils, they are the remains of
organisms that lived long ago. Organisms
are plants, animals, and other living
things.
How Fossil Fuels Formed
Fossil fuels formed in the ground hundreds
of millions of years ago. Dead
organisms sank into mud and rock.
Over time many layers of rock built up.
The remains of the organisms slowly
changed in form to become different
kinds of fossil fuels. Coal came from
plants. Petroleum and natural gas came
mainly from microscopic organisms
such as algae.
Uses and Producers
Fossil fuels and their products have
many uses. Power plants use fossil fuels
to produce electricity. People heat their
A rock contains the fossilized skeleton of a
mammal-like reptile. This animal lived more
than 200 million years ago.
Fossil fuels
contain an
element (basic
substance)
called carbon.
The burning of
fossil fuels
sends carbon
into the air in
the form of a
gas called carbon
dioxide.
BRITANNICA STUDENT ENCYCLOPEDIA Fossil Fuel 55
homes and other buildings by burning
fossil fuels. Gasoline, a product made
from petroleum, fuels cars and other
kinds of motorized equipment.
Many countries produce fossil fuels. The
greatest producer of petroleum is Saudi
Arabia. Russia has the largest reserves of
natural gas. Major coal-producing countries
include the United States and
China. The United States uses more
fossil fuels than any other country.
Disadvantages of Fossil Fuels
Since the late 1700s people have been
using fossil fuels at a faster rate than ever
before. But the planet’s supply of fossil
fuels is limited. Fossil fuels are called
nonrenewable resources. Once they are
used up, they will be gone forever.
The use of fossil fuels harms the environment
as well. When petroleum and
coal burn, they release harmful gases.
These gases react with moisture to create
acid rain, a dangerous form of pollution.
Burning fossil fuels also increases the
temperature of Earth’s atmosphere. This
warming, called the greenhouse effect,
may be harmful to living things.
For these reasons scientists and engineers
have developed new ways to generate
power without using fossil fuels. For
example, some cars are now powered by
electricity instead of gasoline. Homes
can be heated by sunlight. Some electric
power plants run on nuclear energy,
water power, or wind power.
#More to explore
