atmosphere

• what happened in the first billion years of Earth's history?

  volcanoes covering the earth's surface erupted and released lots of gas
• earth's early atmosphere was formed by...

  gas from erupting volcanoes
• Earth's early atmosphere was mostly made up of...

  carbon dioxide and small amounts of nitrogen, with virtually no oxygen (quite like the atmospheres of Mars and Venus today)
• what was Earth's atmosphere like before volcanic activity?


  there was no atmosphere
• why can't scientists be certain about Earth's early atmosphere?

  because it is 4600 years old
• volcanic activity also released...

  nitrogen, water vapour and small amounts of methane and ammonia
• what happened when water vapour in the early atmosphere condensed?

  oceans were formed
• lots of carbon dioxide was removed from the early atmosphere as it...

  dissolved in the oceans
• what happened to dissolved carbon dioxide in the ocean?

  it went through a series of reactions to form carbonate precipitates that formed sediments on the seabed
• what do the skeletons/shells of marine animals contain?

  carbonate precipitates
• green plants and algae in the ocean evolved and...

  absorbed some of the carbon dioxide so they could carry out photosynthesis
• what happened to some carbon in the ocean?

  it got trapped in fossil fuels and rocks
• what happens when plants, plankton and marine animals after death?

  1. they fall to the seabed and get buried by layers of sediment

  2. over millions of years, they become compressed and form sedimentary rocks, oil and gas - trapping the carbon within them (helping to keep it out of the atmosphere)

  3. things like coal, crude oil and natural gas that are made by this process are called 'fossil fuels'

  4. crude oil and natural gas are formed from deposits of plankton. these fossil fuels form reservoirs under the seabed when they get trapped in rocks
• crude oil and natural gas are formed from...

  deposits of plankton - these fossil fuels form reservoirs under the seabed when they get trapped in rocks
• what is coal?


  a sedimentary rock made from thick plant deposits
• what is limestone?


  a sedimentary rock mostly made of calcium carbonate deposits from the shells and skeletons of marine organisms
• green plants and algae in the ocean produced...

  oxygen
• photosynthesis formula


  carbon dioxide + water --> glucose + oxygen

  6CO2 + 6H2O --> C6H12O6 + 6O2
• when did algae evolve?

  2.7 billion years ago (over the next billion years or so, green plants also evolved)
• what happened as oxygen levels built up in the atmosphere?

  more complex life (like animals) evolved
• when did the atmosphere reach a composition similar to today?

  200 million years ago
• what is the composition of today's atmosphere?

  approximately 80% Nitrogen, approximately 20% oxygen and small proportions of various other gases, including carbon dioxide, water vapour and noble gases