Oxygen is the most abundant element in the Earth but dioxygen (O) only started accumulating in the atmosphere well after the formation of the Earth through a biogenic process almost exclusively photosynthesis. O2, is unique in being the only gaseous diatomic molecule with an even number of electrons that is paramagnetic and this explains its relative inertness under ambient conditions.
This article describes the life of the discoverer of O2, Joseph Priestley, and some of the interesting properties of O2.