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The Composition of the Atmosphere The Earth´s atmosphere is a layer of gases surrounding the Earth. The atmosphere is retained by the Earth´s gravity. The Earth is protected by the atmosphere since it absorbs ultraviolet solar radiation, warming the surface through heat retention through a process called the greenhouse effect, and reducing temperature extremes between day and night, which is called the diurnal temperature variation. The atmosphere has a mass of about 5×1018 kg, three quarters of which is within about 11 km of the surface. There is no definite boundary between the atmosphere and outer space, but the atmosphere becomes thinner and thinner with increasing altitude. Atmospheric effects become noticeable during atmospheric reentry of spacecraft at an altitude of 120 km. The boundary between the atmosphere and outer space is called the Karman Line. Atmosphere used in breathing and photosynthesis is air. Dry air contains 78.09% nitrogen, 20.95% oxygen, 0.93% argon, 0.039% carbon dioxide by volume. Air also contains at an average amount of 1% in water vapor.

compounds are included in filtered air. Dust, pollen, spores, sea spray and volcanic ash may be found in tiny amounts in an unfiltered air sample. Composition of the atmosphere by volume: Nitrogen (N2) 780,840 ppmv (78.084%) Oxygen (O2) 209,460 ppmv (20.946%) Argon (Ar)

9,340 ppmv (0.9340%)

Carbon dioxide (CO2) 394.45 ppmv (0.039445%) Neon (Ne)

18.18 ppmv (0.001818%)

Helium (He)

5.24 ppmv (0.000524%)

Methane (CH4)

1.79 ppmv

(0.000179%) Krypton (Kr) Hydrogen (H2)

1.14 ppmv (0.000114%) 0.55 ppmv

(0.000055%) Nitrous oxide (N2O) 0.3 ppmv (0.00003%) Carbon monoxide (CO)

0.1 ppmv

(0.00001%) Air is mainly composed of nitrogen, oxygen, and argon, which together constitute the major gases of the atmosphere. The gases that remain are called trace gases such as greenhouse gases as water vapor, carbon dioxide, methane, nitrous oxide, and ozone. Trace amounts of many other chemical

Xenon (Xe)

0.09 ppmv (9×10−6%)

(0.000009%) Ozone (O3) 7×10−6%)

0.0 to 0.07 ppmv (0 to

Nitrogen dioxide (NO2)

0.02 ppmv

(2×10−6%) (0.000002%) Iodine (I2) (0.000001%)

0.01 ppmv (1×10−6%)

Structure of the Atmosphere

interplanetary space.

The atmosphere is divided into 5 main layers. These layers, from highest to lowest

are: Exosphere: The exosphere is the outermost layer of the atmosphere. It starts at an altitude of about 500 km and goes out to about 10,000 km. Here, particles can travel for hundreds of kilometers before bumping into any other particles of the atmosphere. Particles escape out of the exosphere into deep space. The thermopause is the lower boundary of the exosphere, where it interacts with the thermosphere. It starts at an altitude of about 250-500 km, but its height depends on the amount of solar activity. The top boundary of the exosphere is half way to the moon, or 190,000 km. Here, the solar radiation coming from the sun overcomes the Earth’s gravitational pull on the atmospheric particles. This happens at about 100,000 km from the surface of the Earth, which is considered to be the official boundary between the Earth’s atmosphere and

The exosphere is almost a vacuum. The air is very thin there, and it does not transfer much heat to objects there even though the air is very hot. There are very few particles in the exosphere, and although they are very hot, they do not transfer much energy. The exosphere is sometimes said to be the highest boundary of the thermosphere.

Thermosphere: The thermosphere is the fourth layer of the Earth's atmosphere. Here, the air is also very thin. The temperature in the thermosphere changes based on solar activity, if the sun is active, the temperature increases, and if it is not, then it decreases. Inside the Earth’s thermosphere there is also the ionosphere. The ionosphere is a region of charged particles. The high temperatures in the thermosphere can cause molecules to ionize. This is why an ionosphere and thermosphere can overlap. This layer is the first layer exposed to the sun, so the one that is most heated by it. The name thermosphere comes from the Greek thermo, meaning heat, since it depends on the sun. Because the air is so thin, the exact temperature in the thermosphere has not been able to be calculated. The actual temperature in the Thermosphere can reach as high as 2000º C. thermosphere is located highest above Earth's surface, beginning at about 57 mi (90 km) above Earth, and reaching into about 300 mi (500 km) height.

The air here is warmed because oxygen particles absorb rays from the sun. Because there are relatively few molecules and atoms in the thermosphere, even absorbing small amounts of solar energy can significantly

increase the air temperature, making the thermosphere the hottest layer in the atmosphere. Above 124 mi (200 km), the temperature becomes independent of altitude.

Mesosphere: The mesosphere starts at 50 km above Earth's surface and goes up to 85 km high. The mesosphere is the coldest layer of the Earth’s atmosphere. As you go up the mesosphere, the temperature decreases. The temperature there is around -90° C.

The mesopause is the boundary between the mesosphere and the thermosphere above it. The stratopause is the boundary between the mesosphere and the stratosphere below it. The atmosphere is the hardest layer to study so scientists no less about this layer than the others. Weather balloons and jet planes cannot fly high enough to reach the mesosphere. The orbits of satellites are above the mesosphere. The mesosphere is the layer in which most meteors from space burn up. Also, a special kind of clouds which are very rare, and form much higher than any other clouds, called the "noctilucent clouds" sometimes form in this layer. There are also odd types of lightning in the mesosphere. These types of lightning, called "sprites" and "ELVES", appear dozens of miles above thunderclouds in the troposphere below. Various types of waves and tides in the

atmosphere influence the mesosphere. These waves and tides carry energy from the troposphere and the stratosphere upward into the mesosphere, driving most of its global circulation. The mesosphere is mostly made of oxygen and nitrogen, but it also contains some minor, but very important, gas constituents-chiefly ozone which, although it reaches a maximum in concentration low in the stratosphere, causes a maximum of solar heating near the stratopause. The mesosphere contains the part of the ionosphere known as the D-region, where ionization of molecular (O2) and atomic (O) oxygen releases electrons. This ionization is mainly due to incoming solar radiation, and disappears during the night-one of the reasons why radio reception improves dramatically at night.

Stratosphere: The stratosphere is above tropopause with a height of 50 km. The stratosphere has a strong temperature inversion. Also, it is a stable layer and has a little mixing, so pollutants and other particles may stay in the stratosphere for years. A large concentration of ozone (O3) is found in the stratosphere, with a maximum concentration at about 25 km.

This “ozone layer” absorbs much of the ultraviolet radiation emitted by the sun. Heat is released as the UV is absorbed, which then heats the atmosphere. This explains why temperature increases with height in this layer. Here, temperature increases as altitude increases. The top of the stratosphere has a temperature of about −3°C, which is just a little below of water’s freezing point. The ozone here absorbs UVC and UVB energy from the sun which is broken down into atomic and diatomic oxygen. Absorbing this waves, the stratosphere is protecting the Earth from harmful rays, and because of humans, the ozone layer is being damaged with holes in already some parts of the world.

Troposphere: The troposphere contains approximately 80% of the atmosphere's mass and 99% of its water vapor and aerosols. The troposphere starts at Earth's surface and goes up to a height of 7 to 20 km (4 to 12 miles, or 23,000 to 65,000 feet) above sea level. The troposphere is also called the “zone of weather”. Almost all of the precipitation, winds, storms, and clouds occur here. The troposphere is the lowest part of the atmosphere. Its name comes from the Greek word tropos, which means mixing. As the closest part of the atmosphere to the earth it is subject to the mixing caused by the friction between air and the Earth surface. The zone where this happens in the troposphere is called the planetary boundary layer.

Almost all of the dust particles and water vapor in the atmosphere are found in this layer. The bottom of the troposphere, right next to the surface of Earth, is called the "boundary layer". In Earth, bumpy places such as mountains and hills have higher winds, while smoother surfaces have less wind. The troposphere is heated from below. Sunlight warms the ground or ocean, which in turn radiates the heat into the air right above it. This warm air tends to rise. That keeps the air in the troposphere "stirred up". The top of the troposphere is quite cold. The temperature there is around -55° C. Also,

have you ever wondered why mountain climbers have to take oxygen bottles with them? This is because as altitude increases the air layer gets thinner and thinner and the climbers need this to breathe.

Temperature and Pressure The higher you go, the lesser the air pressure becomes. Atmospheric air pressure is caused by the weight of the air above it. The higher it gets, the less dense the air so there is less weight pressing on the air you are in.

This is the reason why the atmospheric pressure is higher at the sea-levels and lower at mountains and places of high altitudes. With measurements, scientists have been able to see that the relationship between temperature do not happens all through the atmosphere, and this is why they have separated the atmosphere into five layers, and knowing the temperature within each layer they came up with an equation explaining the relationship between temperature, altitude, and pressure.

Life on Earth The atmosphere makes life on Earth suitable because of many reasons. First, the stratosphere protects us from UVB and UVC rays that can damage human’s health. Also, the atmosphere protects us from meteors by burning them or making them smaller. The atmosphere gives us abundant oxygen, essential for us to breathe.

Ozone is concentrated mainly in the stratosphere, where it absorbs solar radiation, protecting Earth's living organisms from the ultraviolet light from the sun. UV radiation is harmful; without the atmosphere's ozone, living organisms could not exist on Earth. UV light causes cancer and cataracts, and it damages DNA. Also, the atmosphere protects us with the Greenhouse effect, which is essential for life on Earth.

The greenhouse effect uses gases, mostly carbon dioxide, to trap unnecessary heat, protecting the Earth from too much heat. It lets the atmosphere function like a blanket, allowing for temperatures hospitable to the planet's life. People exhale carbon dioxide and release it into the atmosphere when burning fossil fuels and plants. Plants absorb carbon dioxide as part of photosynthesis, keeping the carbon and releasing oxygen. Also, the nitrogen in the atmosphere prevents it from burning by combustion. This burning requires oxygen, which is a large part of the atmosphere, but the nitrogen dilutes the oxygen, preventing the Earth from burning. Sadly, we humans are damaging the Earth and atmosphere, leaving ourselves unprotected to these damages. The Earth is heating up with global warming, since holes are appearing on the stratosphere, and unnecessary heat is coming into the Earth, melting ice and damaging our planet.

WORKS CITED “Solar Heating – Geography For Kids – By” Geography & Geology For Kids. 1998. Web. 04 May 2012. <>. "What Are Two Factors That Make Earth Suitable for Life?" WikiAnswers. Answers. Web. 20 May 2012. < ife>. "The Greenhouse Effect." Greenhouse Effect: Background Material. Web. 20 May 2012. <>. "Pressure & Altitude." Pressure & Altitude. Web. 20 May 2012. < ___altitude_16h.html>

"Layers of the Earth's Atmosphere." : Troposphere, Stratosphere, Mesosphere, Thermosphere, and Exosphere. Web. 20 May 2012. <>

The atmosphere  

A description about the comosition of the atmosphere, its layers, and Earth.

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