One source of energy is Natural Gas and it generates my stove, clothes dryer, etc. Another one is biomass energy, it can fuel a furnace/fireplace. Geothermal energy is also one, it helps you to go below or above that temperature that is the house is either cooled or heated.
There are plenty of plants producing oxygen by photosynthesis. Also, human's only use 5% of the oxygen in the air in respiration, there is 21% in the air.
