Childrens Illustrated Encyclopedia

EARTH

170

The
sun is
low in the sky
and days are short,
producing winter.

Sun

FORMATION OF EARTH

Scientists have calculated that Earth

is nearly 4.6 billion years old. Some

moon rocks and meteorites (pieces of

rock that fall to Earth from space) are

the same age, which suggests that

the whole solar system formed

at the same time. The sun, Earth,

and the other planets were

formed from a huge cloud

of gas and dust in space.

EARTH FACTS

Diameter 7,926 miles

at equator (12,756 km)

Diameter 7,900 miles

at poles (12,714 km)

Circumference 24,901 miles

at equator (40,075 km)

Land area 29.2% of Earth’s surface

Ocean area 70.8% of Earth’s surface

Mass 5,900 billion billion tons

(6,000 billion billion tonnes)

Time for 23 hours

one spin 56 minutes 4 seconds

Time to 365 days 6 hours

orbit sun 9 minutes 9 seconds

Distance 93 million miles

from sun (150 million km)

3

Radioactivity in the rocks caused

more heat, and the whole planet

melted. Molten iron then sank to the

center of Earth to form its core.

Lighter rocks floated above the

iron, and about 4.5 billion years

ago the surface cooled to form

the crust. Volcanoes erupted

and poured out gases, which

formed the atmosphere,

and water vapor,

which condensed

(changed into

liquid) to fill

the world’s

oceans.

2

Earth may have taken about

100 million years to grow

into a ball of rock. The new

planet became hot as the

rock particles crashed into

one another.

The surface

was molten,

and young

Earth glowed

red-hot.

SEASONS
Seasons change as Earth moves around the sun. Earth’s axis is not at right
angles to its orbit but tilted over by 23.5°. This makes the poles point
toward or away from the sun at
different times of the year.

Water that

filled the

oceans may

have also

come from

comets that

collided with

young Earth.

4

Tiny living

things began

to grow at least 3.5 billion years

ago. Some produced oxygen,

which began to build up in the

atmosphere about 2.3 billion years

ago. The continents broke up and

slowly moved into their present-day

positions. They are still moving

slowly today, a process called

continental drift.

Find out more

Atmosphere

Climates

Continents

Geology

Oceans and seas

Radioactivity

Rocks and minerals

Universe

The North Pole is tilted

toward the sun.

Here, the sun’s

rays are spread over

a small area in the

Southern Hemisphere,

making summer.

The North

Pole has

winter.

Seasons

are not as

noticeable on the

equator because the equator is

always pointed toward the sun.

GEOTHERMAL ENERGY
The heat from the interior of Earth provides a source of
safe, clean energy, called geothermal energy. Hot rocks
lie close to the surface in Iceland, Italy, and other parts
of the world. The rocks heat underground water and
often make it boil into steam. Wells dug down to these
rocks bring up the steam and hot water, which are used
to generate electricity and to heat buildings.

THEORIES OF EARTH

People once believed that Earth was flat. About

2,500 years ago, the Greeks found out that Earth is

round. Aristarchus, a Greek scientist,

suggested in about 260 bce

that Earth moves around the

sun. It was not until 1543

that Polish astronomer

Nicolaus Copernicus

(1473-1543; right)

reasserted this idea. New

theories are still evolving.

For instance, one idea, called

the Gaia theory, suggests that

the whole planet behaves like

a living organism.

Earth spins 

around its

axis, which passes

through the North

and South Poles.

It also orbits the sun

at the same time.

The sun is higher

in the sky in the

north during

summer.

1

A large clump inside a
cloud of gas and dust
contracted (shrank)
to form the sun about
4.45 billion years ago.
A disk of gas and
dust formed around
the young sun. Small
particles stuck together
and grew into chunks of
rock and ice. Chunks came
together to form planets.