Which gas formed a major part of the early atmosphere?Carbon dioxideNitrogenMethaneAmmonia2The early atmosphere contained a large amount of water vapour. What happened to this?It condensed to form the oceansIt evaporated into spaceIt was used by plants for photosynthesisIt was used by animals for respiration3Which process has reduced the levels of carbon dioxide in the atmosphere to the low levels we have today?Formation of sedimentary rocksAll of theseFormation of fossil fuelsPhotosynthesis4The levels of methane and ammonia in the early atmosphere decreased over time, while the level of nitrogen increased. What is the best explanation for this?Human activities such as burning of fossil fuels and farmingMethane and ammonia are unreactive, while nitrogen reacts with oxygenMethane and ammonia react with oxygen, while nitrogen is unreactivePlants absorb methane and ammonia, and they produce nitrogen5Which two gases together form approximately 99% of the modern atmosphere?Nitrogen and oxygenNitrogen and hydrogenOxygen and hydrogenOxygen and carbon dioxide6Approximately what percentage of carbon dioxide is found in the modern atmosphere?0.9%0.004%1%0.04%