Core Chemistry - Topic 1 The Earth's Sea and 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

• 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

• 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

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