Question

How did oxygen become such a major component of the current atmosphere?

Answer 1

The primary single cell living beings utilized photosynthesis for energy, and oxygen, one of the side-effects of photosynthesis, was delivered into the air in plenitude.

Complete answer:
Clarification: Oxygen has consistently been around in our environment, in any case, since it responds so promptly, it began as generally carbon dioxide, $C{O_2}$. At the point when we talk about barometrical oxygen, generally we allude to diatomic oxygen, ${O_2}$. To expand the convergence of ${O_2}$ we simply need an approach to haul the carbon particle out of the $C{O_2}$ atoms.
Incidentally, photosynthesis does precisely that. During photosynthesis, $C{O_2}$ and water, ${H_2}O$ respond with light to shape glucose and ${O_2}$. Here's a more profound clarification of photosynthesis.

Photosynthesis condition;
$6C{O_2} + 6{H_2}O \to {C_6}{H_{12}}{O_6} + 6{O_2}$
Taking a gander at the synthetic condition above, we can see that carbon particles are pulled off the $C{O_2}$ atoms and added to the water atoms to shape glucose. The ${O_2}$ is then delivered into the environment.
Today, those ${O_2}$ atoms are utilized by creatures during breath to deliver energy. The equation is something contrary to photosynthesis, and converts glucose and oxygen into $C{O_2}$ and water. Breath;
${C_6}{H_{12}}{O_6} + 6{O_2} \to 6C{O_2} + 6{H_2}O$

Before there were creatures, notwithstanding, the ${O_2}$ was allowed to develop in the environment, so as the measure of $C{O_2}$ diminished, the ${O_2}$ expanded, and the air became oxygen rich.
During the Archaean Era, about 3.5 billion years prior, the primary single celled living beings started photosynthesizing. These cyanobacteria siphoned out huge loads of oxygen into the climate.

Note: Oxygen is the compound component with the image O and nuclear number 8. It is an individual from the chalcogen bunch in the occasional table, an exceptionally receptive nonmetal, and an oxidizing specialist that promptly frames oxides with most components just as with different mixtures.