Oxygen is continuously replenished into the Earth’s environment, by the outstanding process of photosynthesis (a process by which light energy from sun splits water molecule to release free oxygen). The aerobic environment and the significantly high concentration of oxygen on earth is attributed to the oxygen cycle. The production of free oxygen on Earth started around 3.5 billion years ago and lead to a gradual increase over the centuries. Oxygen is a major component of the water bodies on Earth and constitutes around 88.8% by mass of oceans. Ozone is present in the upper atmosphere and provides protection against harmful UV rays form sun by absorbing them. Another allotrope of oxygen, known as ozone, is a trioxygen molecule. Oxygen is the 2 nd most abundant component of Earth’s atmosphere (present in about million billion tons or 21% of earth’s atmosphere). It is primarily present in the atmosphere of the Earth and is a major part of gaseous content of the biosphere. The most common allotrope of elemental oxygen is dioxygen O 2. Oxygen is the third most abundant element in the Universe. Oxygen constitutes around 49.2% of Earth’s crust. Biosphere involves the land, sea and air that support life. Oxygen is considered as the most abundant element in the biosphere of Earth, by mass. The name was first proposed by Antoine Lavoisier. The name oxygen originates from combination of two words, oxys and genes, that are Greek word for “acid forming”. In 1774, Carl Wilhelm Scheele and Joseph Priestley independently discovered oxygen, and named it “fire air” and “dephlogisticated air”, respectively due to its role in combustion. Later, John Mayow (1668) proposed that there is a certain element termed as “nitoarial spirit” (for oxygen) present in air that is consumed in combustion and respiration. Robert Hook, in 1665 proposed the presence of unique substance in air that is released when potassium nitrate is heated. The discovery of element as a unique element dates to 2 nd century when Philo observed the association of process of combustion with presence of air.
It is widely used in various manufacturing processes and is the element that sustains the life. Oxygen is a highly reactive non-metal and is one of the most significant elements present on the Earth.