C1.7.2 The Earth's atmosphere

C1.7.2 The Earth's atmosphere

1. For 200 million years, the proportions of gases have been the same as today

   • about four-fifths (80%) nitrogen
   • one-fifth (20%) oxygen
   • small proportions of
     • carbon dioxide
     • water vapour
     • other noble gases

2. first billion years of Earth's existence

   • intense volcanic activity
     • which released the gases that formed the early atmosphere
       • and water vapour that condensed to form the oceans

3. theories about the formation of the atmosphere

   • (we only need to know one)
     • during first billion of year period
       • atmos was mainly carbon dioxide with little/ no oxygen
         • like Mars or Venus today
         • maybe also water vapour an a lil methane and ammonia
           • plants and algae produced oxygen that is now in atmos. and use carbon dioxide in photosynthesis
             • most of carbon 'locked up' in sedimentary rocks as carbonates and fossil fuels
               • carbon dioxide also dissolves in oceans
                 • limestone formed from shells and skeletons of marine organisms
                   • the remains of these contain carbon and hydrocarbons: are fossil fuels
                 • the oceans act as a reservoir for it, but increased amounts impact on marine environment
                   • too acidic for coral and shellfish

4. nowadays, fossilfuels --> releases CO2 --> causes global warming

5. Air is a mixture of gases with diff boiling points

   • fractionally distilled top provide source of raw materials for use in industrial processes
     • 1) air is filtered to remove dust
       • 2) cooled to around -200 degrees, to a liquid
         • during which water vap condenses and is removed
         • 3) C02 freezes, is removed
           • 4) liquefied air enters fractioning column + slowly heated
             • 5) remaing gases separated by fractional distillation
               • oxygen and argon come out together- so another column separates them

6. many theories as to how life developed

   • one: interaction between hydrocarbons, ammonia and lightning
     • supported by Milley-Urey experiment
       • sealed gases in apparatus, heated, applied electrical charge for a week
         • amino acids made, but not as many as there are on Earth
           • suggesting theory isn't quite there
     • 1) lightning- chem recation between gases- amino acids
       • joined together in primordial swamp, a.as join together- organic matter- eventually simple living organisms
         • a body of water from which life eventually crawled