In June 1937 Earhart set out from
Miami, Florida, to fly around the world.
She took along a navigator, Fred
Noonan, to help her find the way. On
July 2 their plane vanished over the
Pacific Ocean. The U.S. Army and Navy
and the Japanese navy sent out searchers.
However, no one ever found the two
fliers or their plane.
In January
1935 Earhart
made a solo
flight from
Hawaii to
California.
She was the
first pilot to
succeed on the
dangerous
route.
Amelia Earhart
88 Earhart, Amelia BRITANNICA STUDENT ENCYCLOPEDIA
Earth
Earth is one of the eight planets that
orbit, or travel around, the sun in the
solar system. It is the third planet from
the sun. Earth travels around the sun at
an average distance of about 93 million
miles (150 million kilometers). It
appears bright and bluish when seen
from outer space.
Earth is the only planet in the solar system
that can support life. Life is possible
on Earth because the planet has water
on its surface and oxygen gas in its air.
Earth also has the perfect range of temperatures
for life. It is not too hot, like
Venus, and not too cold, like Neptune.
The average temperature on Earth is
about 60° F (16° C).
Physical Features
Earth is the fifth largest planet in the
solar system. It is made up of three layers:
the core, the mantle, and the crust.
The core is the center of the planet. It is
about 4,300 miles (6,900 kilometers)
across. The core is very hot. The mantle
covers the core. It is about 1,800 miles
(2,900 kilometers) thick. The crust is
Earth’s thin, rocky outer layer. At its
thickest the crust is about 19 miles (31
kilometers) thick. Plants, animals, and
people live on the crust.
Land covers about 30 percent of Earth’s
surface. The land is divided into seven
huge pieces called continents. These
continents are Africa, Antarctica, Asia,
Australia, Europe, North America, and
South America.
Water covers about 70 percent of Earth’s
surface. This water is in the form of
oceans, rivers, lakes, and groundwater.
The four major water bodies on Earth
are the Arctic, Atlantic, Pacific, and
Indian oceans. They surround the continents.
Some water is frozen. For
example, there are large ice sheets in the
Arctic and Antarctic regions.
The layer of gases surrounding Earth is
called the atmosphere. This is the air
that living things breathe. Earth’s atmosphere
goes up to a few hundred miles
above the surface. The atmosphere gets
thinner as it gets farther from the surface.
It contains mostly water vapor and
the gases nitrogen (77 percent) and oxygen
(21 percent).
The three layers of Earth are the core, the
mantle, and the crust. The crust is the thinnest
layer.
BRITANNICA STUDENT ENCYCLOPEDIA Earth 89
Orbit and Spin
Like all planets, Earth has two types of
motion: orbit and spin. Its orbit is the
path it takes around the sun. It takes
Earth 365.25 days to go around the sun
once. This is equal to one calendar year.
The force that keeps Earth orbiting the
sun is called gravity.
Earth also spins, or rotates around its
axis. The axis is an imaginary line that
runs through Earth’s center from the
North Pole to the South Pole. Earth
completes one rotation in 24 hours.
This is equal to one day.
Seasons
Earth’s axis does not run straight up and
down in relation to the sun. Instead it is
tilted slightly. As Earth moves around
the sun, the North Pole is tilted toward
the sun for about half the year. During
this time the northern half of the planet,
called the Northern Hemisphere, gets
more sunlight than the southern half, or
the Southern Hemisphere. During the
other half of the year the North Pole is
tilted away from the sun. Then the
Southern Hemisphere gets more sun
than the Northern Hemisphere.
These differences in how sunlight hits
different parts of Earth cause the seasons.
For example, the Northern Hemisphere
has its warmest season, summer,
when it is tipped closer to the sun. At
the same time the Southern Hemisphere
has winter, its coldest season.
Satellite
Earth has one natural satellite called the
Moon. A satellite is an object in space
that orbits another object of a larger size.
The Moon is about 239,000 miles
(384,000 kilometers) from Earth.
Earth Through Time
Scientists believe that Earth is about 4.6
billion years old. Earth’s surface has
changed greatly since it was first formed.
Some changes have taken place over
millions of years as wind and water have
eroded, or worn away, the land. Erosion
has created features such as the Grand
Canyon. Other changes have happened
very quickly. The force of an erupting
volcano or an earthquake can change the
surrounding land in just hours.
The scientists who study these changes
are called geologists. They have divided
Earth’s history into time periods called
eons and eras. They use these periods to
explain how and when changes on Earth
took place. For instance, geologists have
found that the Atlantic Ocean was
As seen from outer space, Earth looks like a
bright blue ball with swirling white clouds.
Earth is the
only planet of
the solar
system whose
name does not
come from
Greek or
Roman
mythology.
90 Earth BRITANNICA STUDENT ENCYCLOPEDIA
formed during the Mesozoic era, a division
