Ch. 15- The Earth’s AtmosphereObjectives:

*To explain what the earth’s atmosphere is*To explain how gases in the air cycle

through the environment*To describe the structure of the

atmosphere*To classify clouds

*To explain how precipitation forms*To describe the earth’s wind patterns

Questions you should be able to answer at the end of the lesson.

• What are the two main gases in the atmosphere?

• What living things in soil are needed to change nitrogen into a form plants can use?

• Describe the 4 layers of the atmosphere.• Where is the ozone layer?• What is part of the atmosphere called the

ionosphere?

Lesson 1- The Earth’s Atmosphere

• The Earth’s atmosphere is all around us. – The air we breathe– Clouds – Rainbows show there is moisture in the

atmosphere

Gases in the Atmosphere

• Atmosphere- layer of gases that surround us.• Some other planets have an atmosphere, but

ours is the only one known to support life.• Atmosphere is mostly Nitrogen (78%) and

Oxygen (21%)• Other 1% is a combination of argon, carbon

dioxide, water vapor, neon, helium, krypton, xenon, methane, hydrogen, and ozone

Gases in the Atmosphere

• Oxygen and Nitrogen are needed by all living things.

• Plants and animals take these gases from the atmosphere, use them, then return them to the atmosphere.

• Oxygen and Nitrogen go through these natural cycles over and over.

The Oxygen-Carbon Dioxide CycleAnimals breathe in Oxygen and use it to change the food they eat into energy.

Animals breathe out Carbon dioxide.

Plants take in the Carbon dioxide and use it with the energy from the sun and water to make sugars.

Plants release Oxygen.

• All living thing need nitrogen, but most can not get it directly from the air.

The Nitrogen CycleNitrogen is returned to the soil in animal waste or when plants or animals die.

Bacteria in the soil can use the nitrogen in the air can change the gas into chemical compounds that plants can use.

Animals that eat plants or other plant eating animals get the nitrogen that way.

Bacteria in the soil break down the waste and return the nitrogen to the atmosphere and soil.

Layers of the Atmosphere- Troposphere

• Troposphere- layer you live in. From surface of the earth to 16 km.– Air particles are packed

more tightly. Even though it is the smallest, it contains about 75% of all air particles.

– Air gets colder and less dense as you go up.

– Most clouds you see are in the troposphere.

Layers of the Atmosphere- Stratosphere

• Stratosphere- 16-50 km above the earth’s surface. – Clear and dry.– Temperature increases with

increased height.– Ozone layer is the lower half

of the stratosphere.– Ozone layer absorbs

harmful radiation from the sun.

Layers of the Atmosphere- Mesosphere• Mesosphere- 50-80 km.

– Temperature decreases with increased height– Coldest layer of the atmosphere

* Thermosphere- thinnest air– Temperature increases with height- can reach 2000oC because nitrogen and oxygen absorb the suns energy- the energy strips the electrons from these atoms making

them electrically charged particles (ions) – mostly found between 60-300km above the earth= called the ionosphere

– Ionosphere- Am radio waves bounce off ions in the ionosphere and travel back to Earth so can hear the radio station far away from where it is being broadcast, even more at night when the sun’s energy does not cause interference.

Objective Recap:

• What are the two main gases in the atmosphere?

• What living things in soil are needed to change nitrogen into a form plants can use?

• Describe the 4 layers of the atmosphere.• Where is the ozone layer?• What is part of the atmosphere called the

ionosphere?

Lesson 2- Clouds

• Objectives: – Explain how clouds form.– Identify 3 kinds of clouds.– Explain how precipitation forms.

Questions you should know by the end of the lesson:

• What is a cloud?• Describe two ways a cloud forms.• Explain how fog forms.• Compare cumulus and cirrus clouds.• Name and describe the type of cloud that may

indicate rain.

How Clouds Form• Water evaporates-

changes into a gas called Water Vapor– Becomes part of the air

• Is water vapor hotter or colder than liquid water?

• Are the particles of liquid water moving faster or slower than water vapor?

• So water vapor rises because it is hotter

How Clouds Form• In the troposphere, it gets

colder as you go up, so as water vapor rises, it condenses- changes back in to liquid water. (tiny water droplets suspended in the air)

• When enough water vapor condenses it forms a cloud.

• When air is forced up a mountain it also cools and condenses forming a cloud.

How Clouds Form

• Why can you see your breath on a cold day, but not hot?

• Breath has water vapor. On a cold day the water vapor condenses faster so see it as a cloud.

Types of Clouds

• Clouds are grouped by shape and altitude (height)

Types of Clouds- Stratus Cloud• Low, flat clouds that form in layers• Altitude= Less than 2000 meters• Are wider than high and often cover the whole sky• See grey bottom because block the sun• Often bring rain• Water droplets in clouds stay suspended in the air

by air currents but if grow large enough then fall to Earth as precipitation

• Precipitation can be: rain, snow, hail, and sleet.

Types of Clouds- Stratus Cloud

• Stratus cloud near the ground is called fog• How does fog form? • Without sunlight, the ground cools off quickly

at night. The cool ground cools the air right above it which condenses the water vapor in the air there. Fog usually forms early in the morning after a clear, calm, cold night.

Types of Clouds- Cumulus Clouds

• Puffy, white• Altitude= 2000-7000 meters• Look like pile of cotton balls• Bottoms look gray• Mean fair weather

Types of Clouds- Cirrus Clouds

• Thin, wispy streaks high in the sky• Altitude= 7000-13000 meters• Usually made of ice crystals instead of water

droplets because the air is freezing• Often fair weather, but may mean rain or

snow is on the way

Objective Recap:

• What is a cloud?– A Mass of water droplets in the air

• Describe two ways a cloud forms.– Heat from sun evaporates the water- water vapor

rises and cools as it goes up- water vapor condenses and turns back into a liquid but stays in air as a cloud.

– When air is forced up a mountain it cools and condenses.

Objective Recap: • Explain how fog forms.– At night the ground air and the air above it cool quickly

condensing the water vapor in the air and a cloud forms by the ground.

• Compare cumulus and cirrus clouds.– Cumulus- puffy and white between 2000-7000 meters

from the ground and cirrus clouds are thin and wispy from 7000-13,000 meters about the ground.

• Name and describe the type of cloud that may indicate rain.– Stratus cloud- low, flat clouds in layers- less than 2000

meters about the ground

Lesson 3- Wind Patterns• Objectives: – Explain what causes air to move.– Recognize how air moves in wind cells.– Identify 3 wind belts.

Questions you should be able to answer by the end of the lesson:

• What causes air to move?• What is a wind cell?• Where is the earth’s warmest air?• Where are trade winds found?

From what direction do they blow?

• Does the weather in the United States and southern Canada usually move to the east or west? Why?

Wind Cells

• Atmosphere is constantly in motion.

• Moving air is wind- caused by uneven heating of the earth’s surface by the sun.

• Sun’s energy heats air causing it to expand which makes it lighter (less dense) so it rises. So cold air moves in to take its place which is then warmed= the wind cell.

Wind Cells• Wind Cell- continuous

cycle of rising warm air and falling cold air.

• Warmest air is over the equator- as this air heats, it rises and moves toward the North and South Poles, where the air gets colder and moves back toward the equator.

Global Winds• Wind Belts- pattern of wind moving around the earth.• Trade winds- strong, reliable wind just north or south

of the equator, blows from the east- Hawaii lies within this wind belt.

Global Winds• Prevailing Westerly- Wind

generally between 30oN and 60oN latitudes (or 30oS and 60oS) blows form the west (opposite direction of trade winds) and are not as predictable as the winds in other belts.

• Polar Easterly- Wind near a pole; blows from the east- like trade winds toward warmer latitudes. Bring cold, stormy weather- most of Alaska lies in this belt.

Objective Recap: • What causes air to move?

– Unequal heating of Earth’s surface by the sun.• What is a wind cell?

– Continuous cycle of rising warm air and falling cold• Where is the earth’s warmest air?

– equator• Where are trade winds found? From what direction do they

blow?– Just north and south of the equator. Blow from northeast in Northern

Hemisphere and southeast in Southern Hemisphere• Does the weather in the United States and southern Canada

usually move to the east or west? Why? – Most of US and southern Canada are in a prevailing westerly, which

carries weather from west to east