Earth's Atmosphere: Composition, Layers & Temperature

Composition of the Atmosphere

• The atmosphere consists of a mixture of gases enveloping Earth
• Air pressure diminishes with higher altitude due to fewer air molecules
• The atmosphere is composed of 78% nitrogen, 21% oxygen, and 1% other/trace gases

Layers of the Atmosphere

• The Earth's atmosphere has five layers: troposphere, stratosphere, mesosphere, thermosphere, and exosphere
• The exosphere is the highest layer and the troposphere is the lowest layer
• The region between each layer is called a "pause"

Temperature Variation

• The temperature alternates between getting colder and hotter when moving through the atmosphere
• Thermosphere and stratosphere temperatures get warmer with height
• Mesosphere and troposphere temperatures get colder with height
• Boundaries of each layer are determined by these temperature direction changes

Air Pressure

• Air pressure decreases when moving upwards through the atmosphere
• The troposphere’s bottom has the highest air pressure

Troposphere

• The troposphere is the lowest atmospheric layer
• Extends from ground level to roughly 15 km in the air
• Temperature decreases with height
• Buildings, trees, mountains, birds, clouds, weather, and sometimes planes are in this layer
• Average temperature at the bottom of the troposphere is 18 degrees Celsius
• Temperature at the tropopause decreases to -60 degrees Celsius

Stratosphere

• The stratosphere is the second layer of the atmosphere
• Extends from 15 km to about 50 km above the surface
• Temperature increases with height
• The ozone layer, weather balloons, planes, and jets are in the stratosphere
• Average temperature in the stratosphere ranges from -60 degrees Celsius at the bottom to 0 degrees Celsius at the top

Ozone Layer

• The ozone layer is made of O3 molecules (three oxygen atoms bonded together)
• Protects from harmful UV radiation that can cause sunburn and skin cancer
• Holes were discovered above the North and South Poles in the 1970s/1980s
• These holes were caused by human-made substances
• The Montreal Protocol in 1987 regulated those harmful substances

Mesosphere

• The mesosphere is the third layer of the atmosphere
• Extends from about 50 km to 85 km above the surface
• Temperature decreases with height in this layer
• Meteors disintegrate in this layer due to friction, creating "shooting stars"
• Temperatures range from 0 degrees Celsius at the bottom to -90 degrees Celsius at the top

Thermosphere

• The thermosphere is the fourth layer of the atmosphere
• Extends from about 85 km to 560 km above the surface
• Temperature increases with height
• Aurora Borealis, the retired space shuttle, and the International Space Station (ISS) are in this layer
• Prefix "thermo-" means heat
• The hottest layer by average temperature
• The temperature at the bottom of the thermosphere is -90 degrees Celsius
• Temps increase to as high as 1,500 degrees Celsius

Exosphere

• The exosphere is the fifth and highest atmospheric layer
• Extends from about 560 km to 10,000 km above the surface
• Transition area into outer space
• Contains helium (71%) instead of nitrogen
• Some scientists consider the exosphere part of outer space, not Earth’s atmosphere