of the Atlantics islands. Examples
include the Cape Verde Islands, near
Africa, and Bermuda, near North
America. Iceland is a volcanic island that
rises from the Mid-Atlantic Ridge.
Other Atlantic islands are parts of the
same land as nearby continents.
Examples include the islands of Great
Britain, near Europe, and the Falkland
Islands, near South America.
Currents and Climate
The waters of the ocean move in patterns
called currents. Currents carry heat
and affect climate. In general, the main
currents of the Atlantic Ocean move in a
clockwise direction in the northern part
of the ocean. In the southern part they
move in a counterclockwise direction. At
the equator, the currents move from east
to west. There the water picks up heat.
The water then slowly cools as the currents
move away from the equator.
Large, circular storms called hurricanes
often develop in the warm parts of the
Atlantic. Hurricanes usually hit coastal
areas in the Caribbean Sea and southeastern
North America.
Economy
The Atlantic produces much of the
worlds fish. The ocean is also a source
of many minerals. Large deposits of oil,
natural gas, and coal are found in the
Atlantic. In addition, many cargo ships
use the ocean as a trade route.
Exploration
The ancient Egyptians, Celts (Europeans),
Phoenicians (Middle Easterners),
and Romans sailed on the Atlantic. No
one knows how far west they went, however.
In about AD 1000 Vikings from
northern Europe crossed the Atlantic.
They probably reached the island of
Newfoundland, off the coast of North
America.
In 1492 Christopher Columbus made
his famous voyage across the Atlantic in
search of a new trading route to Asia. In
1520 Ferdinand Magellan sailed around
South America. He discovered the strait
(passage), now named after him, that
links the Atlantic and Pacific oceans.
Environmental Issues
Humans have heavily polluted some
areas of the Atlantic Ocean. This pollution
includes sewage from cities, waste
from factories, and fertilizers and pesticides
from farms. Oil spills from ships or
offshore oil wells are sources of pollution,
too.
A hurricane swirls off the eastern coast of
the United States. Hurricanes often form
over the warm waters of the Atlantic Ocean.
BRITANNICA STUDENT ENCYCLOPEDIA Atlantic Ocean 221
Overfishing is another important environmental
issue in the Atlantic. So many
fish have been caught that some types
are in danger of disappearing entirely.
Some countries have set limits on how
many fish can be caught in certain areas.
They have also set up programs to protect
the fish that are left and to rebuild
the fish populations.
#More to explore
Ocean Pacific Ocean
Atlas
In ancient Greek mythology Atlas was
doomed to carry the heavens on his
shoulders. In some stories, he had to
support the pillars that separate heaven
and Earth. Artists often pictured him
carrying the heavens or a globe.
Atlas mother was Clymene, a minor
goddess known as a nymph. His father
was Iapetus, a Titan. The Titans were
giants who ruled the world. Atlas fought
with the Titans in a war against Zeus.
When Zeus won the war, he became
chief god. Zeus punished Atlas by making
him hold up the sky.
Another story told that Atlas was the
father of nymphs called the Hesperides.
They guarded a tree that bore golden
apples. The hero Heracles (Hercules)
had to perform 12 tasks to make up for
killing his children. One of these tasks
was to steal the golden apples. Heracles
asked Atlas to help. He offered to carry
the heavens for Atlas while Atlas got the
apples. Atlas agreed and fetched the
apples. He planned to refuse to take
back the heavens. But Heracles tricked
Atlas into picking up his burden again.
In another story Perseus turned Atlas into
a mountain by showing him the head
of the monsterMedusa. The Atlas
Mountains of Africa were named for him.
#More to explore
Greece, Ancient Heracles Mythology
Titans Zeus
222 Atlas BRITANNICA STUDENT ENCYCLOPEDIA
Atlas
An atlas is a bound collection of maps.
Atlases vary in size and in the information
presented. Some travelers carry
small atlases that give road and street
directions. Other atlases are huge, very
detailed books that need a reading stand
for support. A general reference atlas
focuses on place locations. A specialsubject
atlas deals with a single subject,
such as agriculture or climate.
In Greek mythology Atlas was a giant
condemned to hold up the heavens. In
the 1500s a man named Gerardus Mercator
put together a collection of maps.
His collection included a picture of Atlas
holding a globe on his shoulders. From
then on, the word atlas was commonly
used to describe a collection of maps.
#More to explore
Map and Globe
Atmosphere
The atmosphere is the layer of gas that
surrounds Earth. It is often called air.
Other planets, and some of their larger
moons, also have atmospheres.
Earths atmosphere consists of several
different gases. The gases are held close
to Earth by a force called gravity. Near
Earths surface, the atmosphere is about
three fourths nitrogen and one fifth oxygen.
At higher elevations, the atmosphere
is mostly hydrogen and helium.
Surprisingly, air has weight. It is heaviest
at sea level. There the gas particles are
pressed together by the weight of the air
above them. Air becomes lighter away
from Earths surface.
Scientists divide the atmosphere into
five regions, or layers. The layer closest
to Earth is the troposphere. It extends
up to about 6 miles (10 kilometers)
above Earths surface. Most of Earths
weather, including the wind and most
clouds, exists in the troposphere.
The second layer, the stratosphere,
extends to about 30 miles (50 kilometers)
above Earths surface. The stratosphere
includes the ozone layer. Ozone
blocks much of the suns radiation that
would harm plants and animals if it
reached Earth.
The third layer is the mesosphere. It
extends up to about 50 miles (80 kilometers)
above Earths surface.
The fourth layer, the thermosphere,
ranges from about 50 to 300 miles (80
to 480 kilometers) above Earth.
The fifth and highest layer of the atmosphere
is the exosphere. This layer ends
An atlas can teach children about the world.
The atmosphere
protects
Earths
surface from
being hit by
objects from
outer space.
These objects
are called
meteoroids.
Most burn up
as they enter
the atmosphere.
BRITANNICA STUDENT ENCYCLOPEDIA Atmosphere 223
where Earths gravity is too weak to prevent
particles of gas from drifting into
space.
Atom
The tiny particles called atoms are the
basic building blocks of all matter.
Atoms can be combined with other
atoms to form molecules, but they cannot
be divided into smaller parts by
ordinary means.
The word atom comes from the Greek
word atomos, meaning indivisible. The
ancient Greeks were the first to think of
the atom as the basic unit of all matter.
It was not until the early 1800s, though,
that scientists began to understand how
atoms work.
Structure