c9

Question 1

explain the changes in the earth’s early atmosphere to form the earth today (6)

Answer 1

• volcanic activity released water vapour
• water vapour condensed to form oceans
• carbon dioxide dissolved in oceans decreasing carbon dioxide
• carbonated produce sediments
• carbon locked up in sedimentary rock
• algae and plants evolve
• absorb carbon dioxide by photosynthesis
• also releases oxygen
• carbon locked up in fossil fuels

Question 2

describe how sewage is treated to remove organic matter (4)

Answer 2

• screening/ grit removal (filter to remove large solids)
• sedimentation to produce sewage sludge and effluent
• anaerobic digestion of sludge
• aerobic biological treatment of effluent