met blacks from many countries. He
became very interested in African history
and culture.
Garvey returned to Jamaica in 1914. He
founded a group known as the Universal
Negro Improvement Association
(UNIA). In 1916 Garvey went to the
United States to start UNIA offices
there.
Garvey taught that blacks would be
respected only when they were successful
in business. He started a newspaper and
several companies. He also promised to
create a black-governed country in
Africa. At that time European countries
ruled nearly all of Africa as colonies.
In the early 1920s Garvey was found
guilty of fraud (cheating people out of
money). He lost many of his supporters
and spent two years in jail. After being
released in 1927, Garvey was forced to
leave the United States. Garvey died in
London on June 10, 1940.
#More to explore
Jamaica
Gas, Natural
Many stoves and home furnaces burn a
fuel called natural gas. Natural gas is
really a mixture of several different gases
that formed slowly beneath Earth’s surface.
How Natural Gas Formed
Natural gas often formed along with
petroleum (oil) hundreds of millions of
years ago. As plants and tiny animals
died, their remains built up in many
layers. Underground pressure and heat
gradually changed the remains into gas
and petroleum.
Types of Gas
The gases that make up natural gas
include methane, ethane, propane,
butane, and other substances. Because
these gases burn very easily, they are
valuable as fuels.
Gas may also be made from coal and
petroleum. This type of gas is called
manufactured gas.
Marcus Garvey was named
Jamaica’s first national hero in
1964.
Russia has the
largest group
of natural gas
reservoirs in
the world.
BRITANNICA STUDENT ENCYCLOPEDIA Gas, Natural 91
Mining and Transportation
Natural gas may be trapped in an underground
pocket, or reservoir, above a
deposit of petroleum. Natural gas may
also be trapped in its own reservoir.
To get natural gas out of the ground,
workers drill a well into the gas reservoir.
The gas rises through a pipe to the surface.
Special equipment then purifies, or
cleans, the gas.
The clean gas may be stored underground
or sent through pipelines to
where it is needed. Gas pipelines can be
hundreds of miles long. Natural gas may
also be cooled into a liquid form and
then shipped in tanks.
#More to explore
Fossil Fuel • Petroleum
Gecko
Geckos are small lizards known for their
incredible climbing ability. There are
about 750 species, or kinds, of gecko.
They live in warm areas of the world in
a variety of habitats, from rain forests to
deserts.
Geckos are among the world’s smallest
lizards. Most species are 1 to 6 inches (3
to 15 centimeters) long, including the
tail. Geckos have a short, stout body and
soft skin. Most are gray, brown, or dirty
white, but a few kinds are green.
A gecko can climb very well because of
the way its feet are designed. Each of its
toes has thousands of tiny hairs on the
bottom. At the end of each hair are hundreds
of even tinier pads. As a gecko
climbs, these pads spread out to create a
strong sticking power. They allow a
gecko to climb up polished glass walls
and even run across ceilings.
Geckos usually are active at night, when
they feed on insects. Unlike other rep-
A pumping station in Russia moves natural
gas through a pipeline.
Geckos are great climbers
because their feet stick to many
surfaces.
92 Gecko BRITANNICA STUDENT ENCYCLOPEDIA
tiles, most geckos have a voice. Their
sounds range from soft clicks or chirps
to sharp cackles or barks.
#More to explore
Lizard • Reptile
Gems
#see Jewelry and Gems.
Genetics
Genetics is the study of heredity, or how
certain features pass from parents to their
offspring, or young. Every kind of plant
and animal produces young of its own
species, or type. The young resemble
their parents. But offspring are not
usually exactly the same as their parents.
For example, their hair color or height
may be different. Genetics explains how
offspring get some of their parents’
features, or traits, but not others.
Genes, Chromosomes, and
Reproduction
Genes are the basic units of heredity.
They carry information about a living
thing, including its traits. Genes exist
inside the cells that make up living
things. Threadlike structures called chromosomes
carry the genes. Each chromosome
is made up mainly of a substance
called deoxyribonucleic acid, or DNA.
The genes are short sections of DNA.
In human beings most cells have 23
pairs of chromosomes, or 46 in all. The
sex cells—sperm cells and egg cells—
each have only one set of 23 chromosomes.
This is because of the way
reproduction works. Every human baby
begins as an egg cell from the mother.
First, though, a sperm cell from the
father must enter the egg. When this
happens, the sperm’s chromosomes
unite with the chromosomes from the
egg. Together they form 23 pairs of
chromosomes. The egg then begins to
divide over and over to grow into a baby.
As the baby grows, each of its cells gets a
copy of the original chromosomes.
A Boy or a Girl?
One pair of chromosomes in a baby
causes it to be a boy or a girl. This pair
consists of chromosomes labeled X or Y.
