the evolution of the atmosphere

• what is the composition of the earths atmosphere today?

  • 80% nitrogen
  • 20% oxygen
  • <1% other gases
• how many years has the earths atmosphere been evolving?

  4.6 billion
• what was the earth like in its first billion years?

  • really dry surface
  • intense volcanic activity
  • mostly carbon dioxide
• what did the intense volcanic activity produce?

  loads of:

  • carbon dioxide
  • water vapour
  • nitrogen

  smaller amounts of:

  • methane
  • ammonia
• how did our oceans form?

  the water vapour from the volcanos condensed into liquid water. this allowed lots of the carbon dioxide form the atmosphere to dissolve in them.
• what did the carbon go on to form in the ocean after dissolving?

  carbon precipitates and then finally become sediments on the sea bed
• when did the second major change involving green plants take place?

  about 2.7b billion years ago
• why did algae and green plants massively change the atmosphere?

  they both need to photosynthesise, meaning the not only need to take in carbon dioxide but the also need to produce oxygen. this means over the past few billion years the amount o carbon dioxide in the atmosphere has slowly declined while the amount of oxygen in the atmosphere have slowly built up.
• what did the increase of oxygen in the atmosphere allow?

  more complex life like animals to evolve
• what happened when the algae and green plants died?

  1. they fell to the sea bed
  2. became buried in layers of sediment
  3. over millions of years this sediment became compressed to form sedimentary rock, oil and gas.
  4. this trapped the carbon to stop it from getting back into the atmosphere.
• what were crude oil and natural gas formed from?

  daily from dead plankton. a diverse group of tiny organisms that float in the ocean
• what was coal formed from?

  coal is a type of sedimentary rock made from thick deposits of dead plant material
• what was limestone formed from?

  limestone is a type of sedimentary rock made from calcium carbonate that marine organisms incorporate into their shells and skeletons