water on earth

In warm areas, ocean water has high salinity, because water there evaporates quickly.. warm current cold current Map Legend 5 Temperature The temperature of ocean water is different in

by Anna Padilla Scott Foresman Science 5.7

• Maps

• Diagrams

• Glossary

Water on Earth

ISBN 0-328-13934-3

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Earth Science

by Anna Padilla Scott Foresman Science 5.7

• Maps

• Diagrams

• Glossary

Water on Earth

ISBN 0-328-13934-3

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Earth Science

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ISBN: 0-328-13934-3

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3 4 5 6 7 8 9 10 V010 13 12 11 10 09 08 07 06 05

Vocabulary

aquifer

condensation

evaporation

precipitation

reservoir

salinity

sleet

sublimation

water table

What did you learn?

1 Why is there sometimes warm water near the poles?

2 What are three ways that water leaves lakes?

3 What is the difference between sleet and freezing rain?

from an aquifer On your own paper, write to explain why people should not take more water from an aquifer than they need Include details from the book to support your answer

Water on Earth

by Anna Padilla

How can the oceans

be described?

The Hydrosphere

Most of Earth is covered with water All of this water is

very important to humans It gives us a way to travel and

a good source of food More than half of the people in the

United States live within 80 kilometers of an ocean

All of Earth’s waters together are called the hydrosphere

Ocean water makes up most of the hydrosphere

The Pacific is the largest ocean It is also the deepest In its deepest spot, it is more than 11,000 meters deep After the Pacific, the largest oceans are the Atlantic, the Indian, and the Arctic If you look at a globe, you will see that all of the world’s oceans are connected

The oceans are all a little different from each other Some oceans have more storms than others They have different average temperatures and different amounts of salt The levels

of the ocean’s surfaces, or sea levels, are also a bit different

Salinity

What is the difference between lake water and ocean water?

If you taste them both, you will notice that ocean water is very

salty Salinity is a measure of how salty water is If you drink

too much ocean water, it can make you sick

The oceans get their salt from rivers Rivers dissolve tiny

amounts of salt from rocks and soil They carry this salt to the

ocean There, some of the water evaporates, leaving its salt

behind Ocean water is more salty in some places than others

In warm areas, ocean water has high salinity, because water

there evaporates quickly Places where rivers flow into oceans

have low salinity

Different salinities help make the ocean’s currents Saltier

water is heavier than less salty water, so it sinks This sinking

can cause currents Most currents are caused by winds

warm current

cold current

Map Legend

5

Temperature

The temperature of ocean water is different in different places Distance from the equator affects water temperature

Water near the equator is usually very warm Water near the North and South Poles is usually very cold

Oceans’ currents also affect water temperature They can carry warm water toward the poles They can also carry cold water toward the equator Look at the map below to see how these currents move

Ocean Resources

We get many products from the ocean We get tuna and other fish to eat We can also get salt from ocean water This

is done by letting the water flow into shallow ponds The water evaporates The salt is left behind

We can drink ocean water if the salt is taken out This way

of getting drinking water costs

a lot of money So it is not very common

This map shows currents on the surface of the water Currents below the surface move in different ways.

Where is fresh water found?

Fresh Water

Less than 1003 of Earth’s water is fresh water Humans need

fresh water to drink We also use it for cooking, cleaning, and

watering crops

Almost all of Earth’s fresh water starts as rain or snow Some

of this water soaks into the ground Some collects in rivers and

lakes Some is frozen in ice sheets and glaciers

Some places have plenty of fresh water Other places do

not have enough for the people who live there No place has

unlimited fresh water People must be careful not to use too

much Water should be used wisely

6

Groundwater

Rain or melted snow that sinks into the ground is called groundwater As it sinks, this water fills spaces between small bits of soil and rock It keeps sinking until it reaches something

it cannot pass through, such as rock or clay A layer of this material will cause groundwater to flow sideways instead

of down

An aquifer is a layer of rock and soil that contains

groundwater Many people get their water from wells drilled into an aquifer The top level of groundwater in an aquifer is

the water table.

The level of a water table changes It rises when water is added by rain or melting snow It falls when a long time passes without rain The level will also fall when water is pumped out through wells faster than it is replaced

7

Rivers

Rivers, streams, and lakes are surface waters They are

formed by groundwater, rainwater, and melting snow

Water from rain and melting snow flows downhill It flows

in small streams These streams join to form larger streams

and rivers Groundwater also seeps into rivers

Each river collects water from a certain area of land That

area is the river’s watershed Pollution in a watershed’s soil

will flow into the river The river can carry the pollution far

away This can affect ecosystems wherever the river flows

Lakes

Lakes form when water collects in a low spot This happens when water flows into a place surrounded by higher land

Sometimes people build dams to make new lakes These

artificial lakes are called reservoirs Reservoirs are often

created as a place to collect fresh water

When you look at a lake, the water doesn’t seem to be going anywhere But water is leaving lakes all the time It flows into rivers, seeps into the ground, and evaporates into the air

9

Ice

About 107 of Earth’s fresh

water is frozen This frozen

water is difficult for people to

use for drinking It is too far

away from most cities

Much of Earth’s ice is near

the poles Thick ice sheets cover

much of Greenland, which

is near the North Pole They

also cover much of Antarctica

These ice sheets can be several

kilometers thick The North

Pole is covered with ice as well

But there is no land there, so

the ice floats on the ocean

Some glaciers and ice sheets

are smaller than others

Glaciers that form in high

mountain valleys are called

valley glaciers These glaciers

flow downhill slowly They

crush and move the rocks

beneath them, changing the

shape of the land

11

Glaciers and ice sheets form when more snow falls than melts The weight of the new snow presses down on the old snow After many years, the snow at the bottom is squeezed into ice

Icebergs are large chunks of ice floating in the ocean They form when pieces of ice sheets

or glaciers break off and fall into the water Icebergs can be huge One iceberg was twice the size of the state of Rhode Island!

Ice is not salty When ocean water freezes, the salt gets pushed out This makes the ocean saltier where new ice is forming

Getting Water to Homes

How do you get your water? You might just walk to the sink

and turn on the tap But it takes a complex system to get the

water to your sink

People usually get their water from lakes, rivers, or the

ground But any of these sources might be polluted Chemicals

from farming, parking lots, and even lawns get washed into

water supplies by rain Water must be treated before we use it

Lakes and rivers are important sources of drinking water.

12

Average Daily Water Use (Per Person) Toilet Flush

Laundry Shower/

Bath Other

71 L

57 L

49 L

38 L

Getting water to homes and businesses is not easy So we should be careful not to waste water We should use no more than we really need

There are many easy ways to save water You can run the faucet only as long as you need it You can take shorter showers And you can water lawns and gardens in the evening That way, less water will be evaporated by the Sun If a faucet leaks, it should be fixed One dripping faucet can waste gallons

of water every day

13

The drawing on these two pages shows the steps in water

treatment First, water is pumped from the source to a

treatment plant The source may be a well or it may be a lake

As the water enters the plant, screens remove large objects

as water flows through them Next, small bits of dirt floating

in the water are removed To do this, chemicals are added to

the water The chemicals form tiny, sticky particles Bits of dirt

get stuck to the chemical particles The growing particles get

heavier and sink to the bottom of a tank

14

Chemicals are added to stick

to pollutants.

The water and chemicals are mixed.

Screens keep out

large objects.

Heavy pollutants fall to the bottom

of the settling tank.

Water Treatment Plant

Water flows through pipes to homes and businesses in the community

Next, the water is passed through filters The filters are often made of layers of sand and gravel Smaller particles still in the water do not pass through the filters

Finally, other chemicals are added to the water These chemicals kill germs Many treatment plants use a chemical called chlorine Fluoride may be added as well It helps your teeth resist decay

Water flows through sand to filter out small particles.

Chlorine, fluoride, or other chemicals may be added

at the end of treatment.

Gravity pulls water down from the tank

Pumping station

The treated water is pumped to the top

of a water tower

15

16

What is the water cycle?

Water in the Air

Water is all around you all the time You can’t see it because

it is in the form of an invisible gas in the air The gas is called

water vapor

Water vapor makes up only a small fraction of all the gases

in the air Particles of gas in the air are always moving The

pressure of the particles pushing against objects is called air

pressure The higher you go in the atmosphere, the weaker air

pressure becomes

The Water Cycle

Water is always moving and changing form The water

cycle is the movement of water, again and again, through the

environment Look at the picture on these two pages It is a

simple picture of the water cycle

Runoff is water moving downhill.

Precipitation

17

Water often changes form as it goes through the water

cycle In evaporation, liquid water changes to water vapor

This usually happens when water is heated by the Sun In

condensation, water vapor changes to liquid water Water

vapor may turn to droplets of liquid water in clouds This also

happens when dew forms on grass In precipitation, water falls from clouds as rain, snow, sleet, or hail In sublimation,

ice changes directly into water vapor It doesn’t melt first and become water This is what happened when ice cubes shrink after being in a freezer for a long time Some ice in the cubes changes to water vapor

Water vapor may freeze into ice without first becoming liquid The ice crystals that form on surfaces are called frost

Condensation

Many Paths of the Water Cycle

The picture below is a more detailed picture of the water

cycle All water does not cycle forever Some water is broken

down by plants as they make sugar Some water is produced by

living things as they make energy during respiration

As water vapor rises,

it may form a cloud.

Water evaporates with

warm temperatures

and winds.

19

Energy in the Water Cycle

Moving all this water around takes energy It takes energy

to raise water vapor to the clouds It takes energy to move the clouds by wind This energy comes from the Sun

Water vapor gives off energy when it condenses This energy

is heat It warms the air or water in the area

Rain and snow fall to Earth.

Some rain or melted snow soaks into the ground and becomes groundwater.

Water runs off the land into streams and rivers that flow into lakes and oceans.

Groundwater slowly moves through aquifers into rivers, lakes, and the ocean This can take thousands of years.

Very slowly, snow and ice turn into water vapor by sublimation.

How do clouds form?

Temperature and Pressure

Clouds form when water condenses into tiny water droplets

If the cloud forms in cold air, the water droplets may turn into

ice crystals Many clouds are made of ice, even during the

summer This is because temperatures high in the air are often

much cooler than on the ground

Air pressure also affects how clouds form Clouds often form

when air moves up In higher areas, the air pressure is lower

and air expands When it expands, it cools, forming clouds

20

Saucer-shaped clouds can

form when winds blow

over a mountain.

21

Cirrus clouds form at high altitudes

They form more than 6,000 meters above ground They are thin, wispy, and white.

Thunderstorm clouds, called thunderheads, have rising air inside them The bottoms of these clouds may be as low as 1,000 meters above ground They might be as tall as 12,000 meters.

Fog is a cloud at ground level It forms when air near the ground is cool Water vapor condenses and forms a cloud near the ground.

These are low–altitude clouds They are called stratus clouds They cover the whole sky and block out the Sun

Stratus clouds are often seen less than 2,000 meters above ground.

Altocumulus clouds look like small, puffy balls Their sides are white, because sunlight bounces off them The bottoms of these clouds can look dark because sunlight may not reach them The bottoms are 2,000–7,000 meters above ground