There is evidence that the Earth's early atmosphere contained less oxygen, but more carbon dioxide and water vapour, than today. Increased emissions of greenhouse gases are leading to climate change.
Which of the following gases was present in the smallest amounts in the early atmosphere?
What process is thought to have formed the early atmosphere?
Photosynthesis of plants
Respiration of animals
Which three gases are present in the highest amounts in the modern atmosphere?
Nitrogen, oxygen and argon
Nitrogen, oxygen and carbon dioxide
Oxygen, argon and carbon dioxide
What proportion of the atmosphere is carbon dioxide gas?
Why did the proportion of carbon dioxide drop when the Earth started to cool?
The carbon dioxide liquefied
The carbon dioxide dissolved in oceans
The carbon dioxide escaped into space
What was responsible for the historical increase in oxygen in the atmosphere?
What is 'potable water'?
Water that is safe to drink
Water that is sold in bottles
Water that has been used by factories
Why is drinking water chlorinated?
To give the water flavour
To give the water a blue colour
To kill microorganisms
The treatment of waste water produces a sludge as a by-product. What is this sludge used for?
Which process can be used to make drinking water from seawater?