4.2-4.3

The atmosphere is a layer of gases that wraps around Earth like a blanket It holds in heat, contains the air we breathe, protects

living things from the sun’s harmful radiation, and helps the planet recycle its water supply

The atmosphere is made up of nitrogen and oxygen with small amounts of carbon dioxide and water vaporEarth is the only planet who’s atmosphere is formed

of these gasesCarbon dioxide is a greenhouse gas that absorbs

Earth’s heat and keeps the planet warmWater vapor is a greenhouse gas that plays an

important role in weatherEarth’s atmosphere is also made up of particles like

soil, pollen, grains, and soot that help form clouds

Weather: the state of the atmosphere at a certain place and timeIt changes all the timeWe can observe weather by measuring

properties of the air like temperature, humidity, air pressure, and windThese can also help us predict weather

Temperature is how hot or cold something is

Humidity: the amount of water vapor air can holdWarm air holds more water vapor than cool airAir that is humid holds a lot of water vaporHumid air is more likely to produce clouds and

precipitation

Air has weightWe live at the bottom of Earth’s atmosphere, so there is

a lot of air above us The force of the weight of the air pushing down on us is air

pressureAir pressure is not the same everywhere

Temperature affects air pressureLow air pressure

Air gets warmer gas particles get farther apart and rises Rising air presses down with less force and creates a low area

of pressure Clouds form where low pressure forms

High air pressure Air gets cooler gas particles get closer together and sink

Sinking air presses down with more force and creates a high area of pressure

Wind is the movement of air from areas of high pressure to areas of low pressure

When the difference of pressure great, the wind blows faster

When the difference of pressure is small, the wind blows slower