The Atmosphere

The atmosphere is a layer of gases that surround the Earth. These layers differ in temperature, in density,

and in the relative amounts of the different gases that are present.

The two main gases in the atmosphere are nitrogen and oxygen.

Nitrogen makes up about 70% of the atmosphere, Oxygen about 20%, and the rest is a mixture of various other gases such as Carbon Dioxide, Methane, Hydrogen, Neon, etc.

The Atmosphere

Layers of the Atmosphere

troposphere stratosphere mesosphere thermosphere

The Atmosphere

Troposphere: the lowest layer

Temperature drops as altitude increases

The troposphere is the densest layer

Almost all weather occurs in the troposphere.

The Atmosphere

stratosphere: between the troposphere and the mesosphere

temperature increases as altitude increases;

contains the ozone layer

The ozone layer shields living things on Earth’s surface from ultraviolet-radiation damage.

The Atmosphere

mesosphere: the coldest layer of the atmosphere,

temperature decreases as altitude increases

Temperatures in the mesosphere decrease to about -80º C.

The Atmosphere

thermosphere: the uppermost layer of the atmosphere

temperature increases as altitude increases

Temperatures average about 980 °C (1,796 °F) because the small amount of oxygen absorbs intense solar radiation.

The Atmosphere

The ionosphere: the lower thermosphere and upper mesosphere

When solar energy is absorbed, charged ions are formed.

Radio waves are reflected in the ionosphere.

Auroras take place in the ionosphere.

Changes in Earth’s Atmosphere

When Earth began to solidify, about 4.4 billion years ago, volcanic eruptions released a variety of gases.

• The gases released by volcanoes did not include oxygen.

Changes in Earth’s Atmosphere

Photosynthetic bacteria contribute oxygen to the atmosphere.

Organisms evolved photosynthesis, a method of capturing energy from the sun.

Photosynthesis produces oxygen as a waste product.

Gradually the oxygen content increased to what it is today.

Changes in Earth’s Atmosphere

Animals produce carbon dioxide necessary for photosynthesis.

Oxygen breathing organisms evolved and released carbon dioxide as a waste product.

The oxygen-carbon dioxide cycle maintains a balance of atmospheric gases on Earth.

Changes in Earth’s Atmosphere

Human-made chemicals can deplete the ozone layer. Ozone forms when the sun’s

ultraviolet rays strike molecules of O2.

Ozone absorbs much of the sun’s ultraviolet radiation.

Without the ozone layer, ultraviolet radiation would damage living cells.

Chlorofluorocarbons, CFCs, are chemicals that destroy the ozone layer, but are now banned in most countries.

Changes in Earth’s Atmosphere

greenhouse effect: the warming of the surface and lower atmosphere of Earth that occurs when carbon dioxide, water vapor, and other gases in the air absorb and reradiate infrared radiation

Greenhouse gases trap the sun’s heat and keep Earth’s surface warm.

Changes in Earth’s Atmosphere

Too much carbon dioxide may cause global warming/climate change

If too much energy is absorbed by the atmosphere, global temperatures will rise.

Global warming could cause problems, such as rising ocean levels, because of melting polar icecaps, and droughts.

Combustion of coal, oil, and gas has added more carbon dioxide to the air.