Core Chemistry - Topic 1 The Earth's Sea and Atmosphere

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  • Created by: Katie
  • Created on: 15-04-13 21:05

The Early Atmosphere

  • Scientists think the evolution of life on Earth caused the atmosphere to change
  • They study other planets and moons which they believe to have no life
    • these planets haven't changed for billions of years
    • therefore they may resemble the Earth's early atmosphere
  • Volcanoes release large quantities of gases
    • on Earth today they release mainly carbon dioxide and water vapour - small amounts of ammonia, methane and nitrogen
    • believed to be the same gases as the early atmosphere
  • Gases released by volcanoes on other planets - Resemble Earth?
    • Titan - 98% nitrogen
    • Mars & Venus - mainly carbon dioxide
  • Titan has an icy interior not rocky (Earth, Mars, Venus)
    • Earth is more likely to resemble Mars & Venus but not certain
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The Early Atmosphere Continued

  • Little or no oxygen in the early atmosphere
    • volcanoes don't release oxygen
    • Earth's oldest rocks are compound that could only form in the absense of oxygen
  • Earth has cooled over time
    • water vapour from the hot atmosphere cooled and condensed to liquid water
    • this formed the oceans
  • Mainly all just theories
    • limited evidence about the Earth's ealy atmosphere
    • many uncertainities about the theories
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A Changing Atmosphere

  • Carbon dioxide dissolved in oceans when water vapour condensed
    • because of this, about half of the carbon dioxide from the atmosphere was lost
  • Some marine organisms use this carbon dioxide to form their shells
    • calcium carbonate
  • When the creatures died shells became sediment
  • Millions of years, layers of sediment = sedimentary rock
    • limestone is mostly calcium carbonate
  • Scientists believe life on Earth started about 4 billion years ago
  • About 1 billion years ago organisms developed the ability to photosynthesise
    • taking in carbon dioxide and releasing oxygen
  • More photosythesising organisms developed e.g. plants
    • this sped up the rate at which carbon dioxide was removed
    • and oxygen was added
  • The amount of oxygen today can be tested with reactive metals
    • using up oxygen in the air through reactions
    • finds the percentage
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The Atmosphere Today

Nitrogen   78%
Oxygen 21%
Argon 0.9%
CO2 0.04%
OTHER   traces

  • OTHER includes carbon monoxide, methane, nitrogen oxide, sulfur dioxide
    • unreavtive noble gases
  • Natural variation of amounts due to:
    • volcanoes - release sulfur dioxide
    • lightning - nitrogen oxides
  • Human activity variation amounts due to
    • deforestation - fewer trees to remove carbon dioxide from atnosphere by photosythesis
    • burning fossil fuels
    • engines/furnaces
    • cattle/rice fields
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