Naturalists at Large: Atmosphere

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<ul><li> 1. Atmosphere Thin envelope ofWeathergases that surrounds Climate the planet.The state of theWeather conditionsatmosphere at a at a locality averagedgiven place and timeover a specified timeperiod</li></ul> <p> 2. Atmosphere is divided into four distinct zones of contrasting temperature due to differential absorption of solar energy.There is little mixing betweenlayers.As you move higher in altitudethe atmosphere thins out. 3. Troposphere contains about75% of the mass the earths air,but is only about 17km thick.Most weather events occur here.Its composition is uniform dueto mixing caused by winds.Temperatures drop with altitude.The sharp boundary intemperature at the tropopauselimits mixing with upper layers 4. Stratosphere extends to about50km thick.Similar in composition to thetroposphere except in two ways.It contains1000 times less waterand is 1000 times higher inozone.Ozone is produced by lightningand solar irradiation of oxygenmolecules.The Stratosphere is relativelycalm, volcanic ash or humancaused pollution can remain insuspension in the stratospherefor many years. 5. Past and Present CompositionThe composition of the Earths atmosphere has changed since theformation of the Earth. The Earths first atmosphere was mainlyhelium and hydrogen. Volcanic emissions later added carbondioxide, nitrogen, water, sulfur dioxide and other elements. 6. Large amounts of carbon dioxide from volcanoes caused theEarths past climate to be warmer than todays.Without carbon dioxide no life could be present on earth. Primitivebacteria and algae in oceans could now photosynthesis. 7. But no life on land due to solar radiation from the sun.But life in oceans is protected from radiation and candevelop due to presence of carbon-dioxide 8. Free oxygen gas was absent in the earths early atmosphere. Any oxygen produced by photosynthesis reacted with other chemicalsand was trapped in the form of oxide compounds in rock, Fe2O3 .It took millions of years before oxygen was present as a gas in theatmosphereNearly all the molecular oxygen in the atmosphere today wasproduced by photosynthesis.Sunlight + CO2 + H2O O2 (g) + C6H12O6Living organisms are responsible for the evolution of ouratmosphere. Free oxygen made it possible for life to evolve on land.Before large amounts of free oxygen were present in theatmosphere, lethal intensities of solar radiation flooded the Earthssurface.Free oxygen reacts in the stratosphere to form ozone (O3). This ozonelayer shields the Earths Surface from lethal radiation. 9. Oxygen produced by photosynthesis builds up in the atmosphere. Thisturns into ozone due to solar radiation. 10. GasSymbol Percent by VolumeNitrogen N2 78.08 %Oxygen O2 20.94 %ArgonAr 0.934 %Carbon Dioxide CO20.033 %Neon Ne 0.00182 %Helium He 0.00052%MethaneCH40.00015 %KryptonKr 0.00011 %Hydrogen H0.00005 %Nitrous oxideN2O0.00005 %XenonXe 0.000009 %Water vapor varies depending on the location. From 0.01% to 5% 11. Suspended particles within the Atmosphere are called aerosols.Aerosols can be both solid andliquid. Some are too small tosee, other are clustered togetherand can be seen as clouds. Volcanoes are one major source of natural aerosols 12. How does the Earth keep itself warm?The average radiant energy from the sun falling on the surfaceat about 343 watts /m2.As it passes through the atmosphere, 6% is scattered back intospace by atmospheric molecules.10% is reflected back intospace from land and ocean surface.The remaining 84% actually heats up the surface. To balance this the Earth itself needs to radiate the same amount of energy back into space.The Earth emits long-wave length radiation in the form ofinfrared radiation. (this depends on the temperature of thesurface and the type of surface)But the amount of energy is not balanced. 13. Nitrogen and Oxygen gas can neither absorb or emit thermal radiation.It is Water vapor, carbon dioxide, and some other minor gases whichabsorb long-wave thermal radiation leaving the surface. This is why the average surface temperature is 15C instead of -6C which it should be it balanced. 1. Solar radiation 2. Radiation from greenhouse gases 3. Radiation scattered by atmosphere. 14. Some wavelengths of radiation from the Earth can escape into spaceif there are no clouds. Other wavelengths are absorbed by gases andre-emitted into space or back to the surface.Graph of radiation emitted from Earths surface that isabsorbed by the Atmosphere. 15. Absorption of solar energy by the atmosphere is selective.Visible light passes through, ultraviolet is absorbed mostly byozone in the stratosphere. Infrared is absorbed mostly by carbondioxide and water in the troposphere. 16. Solar Radiation and the Atmosphere</p>