The original point of view on the origin and development of oxygen of the atmosphere of planet Earth is popularly presented. It is proved that the first oxygen appeared as a result of degassing of basalt magma and continues to flow from the earth's interior to the present. The intermediate collector of this oxygen is the waters of the oceans. The time for the accumulation of free oxygen in the amount necessary to ensure the life of organisms belongs to the initial stages of the geological development of the planet. Oxygen biogenic, or photosynthetic, appeared somewhat later. These two constantly operating sources of oxygen have the deepest internal connections between them. For a wide range of readers.