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Earth^37

Seasons are regular weather patterns in

different places on the Earth’s surface

caused by the Earth’s tilt. At any time, one

hemisphere (half of Earth above or below

the Equator) leans towards the Sun,

exposing it closer to the Sun’s light and

heat, and bringing warm summer days.

The other half tilts away and has winter.

HOW DOES THE EARTH SUPPORT LIFE?

The Earth is just the right distance from the Sun so that

temperatures are bearable – neither too hot, nor too cold.

The Earth’s atmosphere and oceans also help to control

temperatures. Earth also has air we breathe and

water – both vital for life.

1 EARTH’S ORBIT AND THE SEASONS
When the North Pole tilts towards the Sun, regions in the northern hemisphere
have summer while the southern hemisphere has winter (1). As the Earth continues
on its orbit, the seasons change to autumn in the northern hemisphere and spring in the
southern hemisphere (2). When the South Pole tilts towards the Sun, the southern hemisphere
has summer and it is winter in the north (3). This gradually gives way to autumn in the southern
hemisphere and spring in the northern hemisphere (4) as the Earth continues around the Sun.

HOW DOES EARTH MOVE THROUGH SPACE?

The Earth takes one year, or 365.242 days, to

orbit, or travel, around the Sun. At the same

time, it spins on its axis (an imaginary line

joining the North and South poles). As

it spins, the Earth is tilted on its axis

at an angle of 23.5 ̊. This tilt produces

the. SEASONS.

DO ALL PARTS OF THE EARTH HAVE SEASONS?

Most regions experience seasonal change throughout

the year. However, the seasons are least noticeable in

tropical regions near the Equator (an imaginary line

around the Earth’s middle) because the Equator does

not tilt away from the Sun for part of the year.

4 EARTH’S OCEANS

The Earth’s oceans cover almost two-thirds of its

surface, making the planet look blue from space.

The oceans formed 4,500 million years ago, as

the Earth’s surface cooled.

DAY AND NIGHT 3

Earth spins around once on its

axis every 24 hours. This

brings day to the regions

facing the Sun and night

to those facing away

from the Sun.

Direction of

Earth’s spin

North Pole

South Pole

Axis

1 THE CHANGING SEASONS

Temperate lands lying between tropics and poles have four distinct seasons. In spring, days

become warmer and longer and new leaves sprout on trees. Summer is the warmest season.

In autumn, the days grow cooler and shorter. Winter is the coldest season.

FIND OUT MORE. Asteroids 23 • Atmosphere 49 • Climate Zones 63 • Life on Earth 70–71 • Solar System 14

1 SEASONS IN THE TROPICS

Regions on or near the Equator are hot and wet all year round. Farther

north and south of the Equator are tropical grasslands (above). These are

always hot but have distinct wet and dry seasons.

SEASONS

Continent (large area of land)

Ocean

4,600 million years ago Earth begins to form as a ball of

molten rock.

4,500 million years ago Volcanoes erupt gas and steam to form

the oceans, and molten rock.

4,200 million years ago Earth’s surface cools and the hard

outer crust forms.

4,000 million years ago First signs of life

3,600 million years ago The first continents form; life begins

on Earth.

EARTH’S FORMATION

2

3

1

4

Sun’s rays

Equator