Atmosphere of Earth facts for kids

The atmosphere is the layer of gases around the Earth. It is held in place by Earth's gravity. It is made up mainly of nitrogen (78.1%). It also has plentiful oxygen (20.9%) and small amounts of argon (0.9%), carbon dioxide (~ 0.035%), water vapor, and other gases. The atmosphere protects life on Earth by absorbing (taking) ultraviolet rays from the sun. It makes our days cooler and our nights warmer.

Solid particulates, including ash, dust, volcanic ash, etc. are small parts of atmosphere. They are important in making clouds and fog.

The atmosphere does not end at a specific place. The higher above the Earth, the thinner the atmosphere. There is no clear border between the atmosphere and outer space, though the Kármán line is sometimes treated as a border. Even higher, for some purposes the edge of the magnetosphere is treated as a border. 75% of the atmosphere is within 11 kilometres (6.8 miles) of the Earth's surface.

History of Earth's atmosphere

Originally, the Earth's atmosphere had almost no free oxygen.

1. The first atmosphere consisted of gases in the solar nebula, mainly hydrogen. There might also have been simple hydrides such as those now found in the gas giants (Jupiter and Saturn): water vapor, methane and ammonia.
2. The atmosphere gradually changed to mostly carbon dioxide and nitrogen. The lighter gases, like hydrogen and helium, cannot be held by the Earth's gravity, and would escape. For a long time (say two billion years or more), the atmosphere was dominated by carbon dioxide.
3. In the Great Oxygenation Event the atmosphere changed to the kind we have now, with oxygen replacing the carbon dioxide. Our atmosphere is still mostly nitrogen, but most living organisms interact more with oxygen than with nitrogen. Oxygenation began with cyanobacteria making free oxygen by photosynthesis. Most organisms today need oxygen for their respiration: only a few anaerobic organisms can grow without oxygen.

Temperature and the atmospheric layers

Temperature at various altitudes

Some parts of the atmosphere are hot or cold, depending on height. Starting from the surface and climbing straight up, the air gets colder in the troposphere, but then it becomes hotter, higher in the stratosphere. These changes of temperature are divided into layers. These are like layers of an onion. The difference between the layers is the way the temperature changes.

These are the layers of the atmosphere, starting from the ground:

• Troposphere - Starts at the ground. Ends somewhere between 0 to 18 kilometres (0 to 11 miles). The higher, the colder. Weather in this layer affects our daily life.
• Stratosphere - Starts at 18 kilometres (11 miles). Ends at 50 kilometres (31 miles). The higher, the hotter. The heat comes from the Ozone layer at the top of the stratosphere. There is little water vapor and other substances in this layer. Airplanes fly in this layer because it is usually stable and air resistance is small.
• Mesosphere - Starts at 50 kilometres (31 miles). Ends at 80 or 85 kilometres (50 or 53 miles). The higher, the colder. Winds in this layer are strong, so the temperature is not stable.
• Thermosphere - Starts at 80 or 85 kilometres (50 or 53 miles). Ends at 640 kilometres (400 miles) or higher. The higher, the hotter. This layer is very important in radio communication because it helps to reflect some radio waves.
• Exosphere - Above the thermosphere. This is the top layer, and merges into interplanetary space.

Where one layer changes to the next have been named "-pauses." So the tropopause is where the troposphere ends (7 to 14 kilometres (4.3 to 8.7 miles) high). The stratopause is at the end of the stratosphere. The mesopause is at the end of the mesosphere. These are called boundaries.

The average temperature of the atmosphere at the surface of Earth is 14 °C (57 °F).

Pressure

The atmosphere has pressure. This is because even though air is a gas, it has weight. The average atmospheric pressure at sea level is about 101.4 kilopascals (14.71 psi).

Density and mass

The density of air at sea level is about 1.2 kilograms per cubic meter. This density becomes less at higher altitudes at the same rate that pressure becomes less. The total mass of the atmosphere is about 5.1 × 10¹⁸ kg, which is only a very small part of the Earth's total mass.

Related pages

• Air
• Life timeline

Images for kids

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  2009 NASA photo showing Earth's atmosphere at sunset, with Earth silhouetted

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  Blue light is scattered more than other wavelengths by the gases in the atmosphere, surrounding Earth in a visibly blue layer when seen from space on board the ISS at an altitude of 335 km (208 mi).

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  Mean atmospheric water vapor

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  Space Shuttle Endeavour orbiting in the thermosphere. Because of the angle of the photo, it appears to straddle the stratosphere and mesosphere that actually lie more than 250 km (160 mi) below. The orange layer is the troposphere, which gives way to the whitish stratosphere and then the blue mesosphere.

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  Temperature trends in two thick layers of the atmosphere as measured between January 1979 and December 2005 by microwave sounding units and advanced microwave sounding units on NOAA weather satellites. The instruments record microwaves emitted from oxygen molecules in the atmosphere. Source:

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  Temperature and mass density against altitude from the NRLMSISE-00 standard atmosphere model (the eight dotted lines in each "decade" are at the eight cubes 8, 27, 64, ..., 729)

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  Distortive effect of atmospheric refraction upon the shape of the sun at the horizon.

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  An idealised view of three pairs of large circulation cells.

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  Oxygen content of the atmosphere over the last billion years

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  Earth's atmosphere backlit by the Sun in an eclipse observed from deep space onboard Apollo 12 in 1969.

See also

In Spanish: Atmósfera terrestre para niños