water on earth

what is water

Water is a simple chemical compound. Each molecule of water contains two hydrogen atoms (H2 ) and one oxygen atom (O). Thats why the chemical formula for water is H2 O. If water is so simple, why is it special? Water is one of the few substances that exists on Earth in all three states of matter. Water occurs as a gas, a liquid and a solid. You drink liquid water and use it to shower. You breathe gaseous water vapor in the air. You may go ice skating on a pond covered with solid water ice in the winter.

the water cycle

Did you ever wonder where the water in your glass came from or where its been? The next time you take a drink of water, think about this. Each water molecule has probably been around for billions of years. Thats because Earths water is constantly recycled.

where is earths freshwater

Earth is often called the water planet. Figure 13.1 shows why. If astronauts see Earth from space, this is how it looks. Notice how blue the planet appears. Thats because oceans cover much of Earths surface. Water is also found in the clouds that rise above the planet. Most of Earths water is salt water in the oceans. As Figure 13.2 shows, only 3 percent of Earths water is fresh. Freshwater is water that contains little or no dissolved salt. Most freshwater is frozen in ice caps and glaciers. Glaciers cover the peaks of some tall mountains. For example, the Cascades Mountains in North America and the Alps Mountains in Europe are capped with ice. Ice caps cover vast areas of Antarctica and Greenland. Chunks of ice frequently break off ice caps. They form icebergs that float in the oceans.

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processes in the water cycle

Water keeps changing state as it goes through the water cycle. This means that it can be a solid, liquid, or gas. How does water change state? How does it keep moving through the cycle? As Figure 13.3 shows, several processes are involved. Evaporation changes liquid water to water vapor. Energy from the Sun causes water to evaporate. Most evaporation is from the oceans because they cover so much area. The water vapor rises into the atmosphere. Transpiration is like evaporation because it changes liquid water to water vapor. In transpiration, plants release water vapor through their leaves. This water vapor rises into the atmosphere. Condensation changes water vapor to liquid water. As air rises higher into the atmosphere, it cools. Cool air can hold less water vapor than warm air. So some of the water vapor condenses into water droplets. Water droplets may form clouds. Precipitation is water that falls from clouds to Earths surface. Water droplets in clouds fall to Earth when they become too large to stay aloft. The water falls as rain if the air is warm. If the air is cold, the water may freeze and fall as snow, sleet, or hail. Most precipitation falls into the oceans. Some falls on land. Runoff is precipitation that flows over the surface of the land. This water may travel to a river, lake, or ocean. Runoff may pick up fertilizer and other pollutants and deliver them to the water body where it ends up. In this way, runoff may pollute bodies of water. Infiltration is the process by which water soaks into the ground. Some of the water may seep deep under- ground. Some may stay in the soil, where plants can absorb it with their roots. In all these ways, water keeps cycling. The water cycle repeats over and over again. Who knows? Maybe a water molecule that you drink today once quenched the thirst of a dinosaur.

how water is recycled

Water is recycled through the water cycle. The water cycle is the movement of water through the oceans, atmo- sphere, land, and living things. The water cycle is powered by energy from the Sun. Figure 13.3 diagrams the water cycle.

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instructional diagrams

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questions

About what percent of Earths surface is covered with water?

a. 20 percent

b. 50 percent

-->  c. 70 percent

d. 90 percent

Water is stored in

a. ice and snow

b. the atmosphere

c. lakes and streams

-->  d. all of these

What percent of Earths total water is fresh water?

-->  a. 3 percent

b. 52 percent

c. 79 percent

d. 97 percent

The largest amount of fresh water is contained in

-->  a. ice caps, glaciers and inland seas

b. rivers and streams

c. the oceans

d. groundwater and soil moisture

Most of Earths liquid fresh water is located in

-->  a. underground rocks.

b. living organisms.

c. surface soil.

d. large lakes.

The water cycle

a. begins and ends in the oceans.

-->  b. has no beginning and has no end.

c. begins in the oceans and ends in groundwater aquifers.

d. begins in the atmosphere and ends in the oceans.

The energy for the water cycle comes from

a. radioactive decay

b. Earths internal heat

-->  c. the Sun

d. water when it changes state

Most fresh water enters the atmosphere when water evaporates from

-->  a. oceans.

b. plants.

c. lakes.

d. soils.

Clouds form when water vapor

a. evaporates.

-->  b. condenses.

c. transpires.

d. freezes.

In infiltration, water goes

-->  a. through the ground

b. to the atmosphere by changing from liquid to gas

c. to the atmosphere through a plant

d. none of these.

Forms of precipitation include

a. rain.

b. snow.

c. sleet.

-->  d. all of the above

Water vapor enters the atmosphere through

a. infiltration.

-->  b. transpiration.

c. condensation.

d. two of the above

Icebergs are made of frozen salt water.

a. true

-->  b. false

Almost 80 percent of Earths fresh water is frozen.

-->  a. true

b. false

There is more water in Earths living things than there is in the atmosphere.

a. true

-->  b. false

Soil moisture is important for plants to grow.

-->  a. true

b. false

Some water molecules may be billions of years old.

-->  a. true

b. false

Water exists on Earth in all three states of matter.

-->  a. true

b. false

The water cycle has no beginning or end.

-->  a. true

b. false

Water can go through the water cycle without changing state.

a. true

-->  b. false

Water turns to gas through condensation.

a. true

-->  b. false

Most condensation of water takes place in the oceans.

a. true

-->  b. false

The atoms that make up water molecules come together and break apart easily.

a. true

-->  b. false

Cold air can hold less water than warm air so when air cools water may condense.

-->  a. true

b. false

Water that forms clouds always falls to the ground as precipitation.

a. true

-->  b. false

Runoff may pollute rivers, lakes, and oceans.

-->  a. true

b. false

Most of Earths precipitation falls on land.

a. true

-->  b. false

water that falls from clouds to Earths surface

a. condensation

b. evaporation

c. infiltration

d. water cycle

e. transpiration

-->  f. precipitation

g. runoff

continuous movement of water through the oceans, atmosphere, land, and living things

a. condensation

b. evaporation

c. infiltration

-->  d. water cycle

e. transpiration

f. precipitation

g. runoff

process in which plants release water vapor through their leaves

a. condensation

b. evaporation

c. infiltration

d. water cycle

-->  e. transpiration

f. precipitation

g. runoff

precipitation that flows over the surface of the ground

a. condensation

b. evaporation

c. infiltration

d. water cycle

e. transpiration

f. precipitation

-->  g. runoff

process in which water vapor changes to liquid water

-->  a. condensation

b. evaporation

c. infiltration

d. water cycle

e. transpiration

f. precipitation

g. runoff

process in which liquid water changes to water vapor

a. condensation

-->  b. evaporation

c. infiltration

d. water cycle

e. transpiration

f. precipitation

g. runoff

process in which water soaks into the ground

a. condensation

b. evaporation

-->  c. infiltration

d. water cycle

e. transpiration

f. precipitation

g. runoff

diagram questions

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