What is the significance of the oxygen content in the atmosphere of our planet and its variety, ozone, for living things?

Without oxygen, which is found in two species in the atmosphere, more than half of the animals and plants on earth would die (all organisms need oxygen, but not all breathe atmospheric oxygen). Although oxygen makes up only about 20% of the air we breathe, it is oxygen that the body needs.
Ozone, the second type of this gas, protects us from solar radiation by reflecting deadly rays back into space.