Weather and Climate

Chapter 1The

Atmosphere

Section 1 Key Terms• Weather-

The condition of Earth’s atmosphere at a particular place and time.

• ClimateThe average, year-after-year conditions of temperature, precipitation, winds, and clouds in an area.

• Atmosphere-The layer of air that surrounds Earth.

• Ozone-A form of oxygen that has three oxygen atoms in each molecule instead of the usual two.

ObjectiveThe students will explain

how the atmosphere is important to living

things and identify the gases that make up Earth’s atmosphere.

The Air Around You• Earth’s atmosphere is the covering

of gases that surrounds Earth. Compared to the size of Earth, the atmosphere is a very thin covering.

• The atmosphere is commonly called the air.

• Weather is the condition of Earth’s atmosphere at a particular place and time. For example, the weather you have right now is the condition of the atmosphere at your particular place.

Composition of the Atmosphere

• Nitrogen is the main gas in the atmosphere. Nitrogen gas makes up about 78 percent of the atmosphere.

• Oxygen is the number two gas in the atmosphere. It makes up about 21 percent of the atmosphere.

Composition of the Atmosphere

• Most oxygen molecules in the atmosphere have two oxygen atoms. Another form of oxygen has three atoms instead of two. Ozone is the form of oxygen that has three oxygen atoms.

Composition of the Atmosphere

• Carbon dioxide makes up a tiny portion of the atmosphere. But carbon dioxide is needed for life on Earth. Plants need carbon dioxide to make food.

• The amount of water vapor in the atmosphere varies. Water vapor is the gas form of water.

• The solids in the atmosphere are referred to as particles. Particles in air include dust, smoke, and other chemicals.

Importance of the Atmosphere

• One reason the atmosphere is important is that it contains oxygen and other gases that living things need.

• The atmosphere traps heat energy from the sun. Trapping heat allows living things to live on Earth.

• The atmosphere also prevents Earth from being hit by meteoroids from outer space.

Section 3 Key Terms• Density— The amount of mass of a substance to a

given volume.• Pressure—

The force pushing on an area or surface.• Air pressure—

A force that is the result of the weight of a column of air pushing down on an area.

• Barometer—• An instrument used to measure changes

in air pressure• Altitude—

Elevation above sea level.

ObjectiveThe students will

describe properties of air and name

instruments used to measure air pressure.

Properties of Air• Air has mass. Because air has

mass, it also has density. Density is the amount of mass in a certain volume.

• The more molecules there are in a certain volume, the more mass there is. And the more mass there is, the greater the density. This is true for all substances, including air. Air that has more molecules—more mass—has a greater density.

Properties of Air• Because air has more mass, it

has pressure. Pressure is the force pushing on an area or a surface.

• Air has pressure because air’s mass has weight. The weight of air presses down. Air pressure is the pressing down of the weight of air on an area.

• Denser air has more air pressure than less dense air has.

Measuring Air Pressure A barometer

is an instrument used to measure air pressure. There are two types of barometers, mercury barometers and aneroid barometers.

Measuring Air Pressure• Altitude is the distance above sea

level. Altitude is also called elevation. Sea level is the average level of the ocean’s surface.

• Air at sea level carries the weight of all the air above it. As you go higher, the air has less air on top of it, and therefore, it has less weight pressing on it. So, air pressure at sea level is greater than the air at any place above it.

• Altitude affects density. As you go higher, air becomes less dense. As you go lower, air becomes more dense.

ObjectiveThe students will

describe characteristics of the

main layers of the atmosphere.

Layers of the Atmosphere• Scientists divide

the atmosphere into four layers. They classify these layers by the changes in temperature. As you go from one layer to the next, the temperature changes in a different way.

Layers of the Atmosphere• We live in the troposphere. It is the

lowest layer of the atmosphere. Most weather happens in the troposphere. In the troposphere, the temperature decreases as the altitude increases. In other words, the higher you go in the troposphere, the colder it gets.

Layers of the Atmosphere• The stratosphere is the layer just

above the troposphere. The middle portion of the stratosphere contains the ozone layer, where there is more ozone than in any other part of the atmosphere. In the stratosphere, the temperature increases as the altitude increases. In other words, the higher you go in the stratosphere, the warmer it gets.

Layers of the Atmosphere• The mesosphere is the layer of the

atmosphere just above the stratosphere. In the mesosphere, the temperature decreases as the altitude increases. So, the higher you go, the colder it gets. Most meteoroids from space burn up in the mesosphere.

Layers of the Atmosphere• The top layer of the atmosphere is

called the thermosphere. In the thermosphere, the temperature increases as the altitude increases. So, the higher you go, the higher the temperature is. The thermosphere is divided into two layers, the ionosphere and the exosphere. The exosphere gradually blends with outer space.

Brain Pop•Earth’s Atmosphere•Ozone Layer•Global Warming•Climate Types