homework encyclopedia

52 Earth

The Earth is unusual among the planets in our Solar

System in having an atmosphere that contains

moisture. Moisture in the air gathers in. CLOUDS,

and eventually falls as. SNOW,. HAIL, sleet, or rain.

Any kind of falling moisture is called precipitation.

WHY DOES IT RAIN?

The Sun’s heat causes moisture from oceans and lakes

to evaporate into the air, forming water vapour. The

vapour rises, cools, and condenses (turns into a liquid)

into tiny water droplets, which form clouds. If the

clouds continue to absorb moisture, they become

saturated. The water droplets in the clouds collide and

become bigger and heavier until the air can no longer

support them. Then they fall as rain.

4 RAINBOW

A rainbow forms when sunlight

passes through falling raindrops.

The light is refracted (bent and

split) into the seven colours that

make it up – red, orange, yellow,

green, blue, indigo, and violet.

RAINSTORM 3

Dark storm clouds release lashing

rain in hilly country. The water

collects in lakes in the lowlands

below. Raindrops falling

from storm clouds can be

5 mm (^3 ⁄ 16 in) wide.

Water droplets

too heavy to float

in the air fall to

the ground as rain

Storm clouds

contain billions

of tiny water

droplets, which

make them dark

and grey

Water evaporates

(turns into water vapour)

from lakes and rivers

in the Sun’s heat

Clouds form as water

vapour cools and condenses

into tiny water droplets

Water stored in the

ocean evaporates

and rises into the

atmosphere

THE WATER CYCLE

Water seeps into rock

creating groundwater

(underground water)

Rain and snow fall

on high ground

Rays of sunlight

gleam through

a gap in the clouds

Groundwater flows

into rivers or the ocean

Surface water flows

back to the ocean

Rain falls

over the

ocean

Water vapour is

given out by

plants

DO SOME PARTS OF THE WORLD

RECEIVE MORE RAIN THAN OTHERS?

Around the world, rainfall patterns vary widely.

In some regions rain falls almost daily. In deserts,

it may not rain for years. The tropics are generally

wet, while the polar regions are dry because moisture

there is locked up in the form of ice.

The water on Earth is constantly recycled between

the oceans, land, and atmosphere. The water cycle,

or hydrological cycle, is driven by the Sun’s heat.

Life-giving rain feeds streams, rivers, and lakes. It

waters plants so they can grow, and gives animals

and people vital moisture.

Rain

rain