Question

How oxygen origin in earth?

Answer 1

Oxygen was a part of Earth from the earliest times, but at first almost all oxygen on the planet was chemically bound in both organic and inorganic compounds, as well as in abundant molecules such as water and carbon dioxide.

Oxygen is exceedingly reactive, and iron is one of the most common elements in the Earth's crust. In the early history of Earth, most iron at or near the surface of the Earth was not yet oxidized, so free oxygen was quickly absorbed into the Earth's crust. The lack of free oxygen in the atmosphere probably prevented more advanced organisms from developing. The earliest life forms were based on anaerobic metabolisms, although aerobic metabolism offers great advantages. Since free oxygen was quickly absorbed, it was impossible for organisms based on aerobic metabolism to develop.

Cyanobacteria developed perhaps a few hundred million years before what is now described as the "Great Oxidization Event" of around 2.4 billion years BP. Cyanobacteria produce oxygen through photosynthesis, and the oxygen they emit eventually saturated the reducing iron (as well as other mineral and organic sinks) near the surface of the Earth's crust. As the supply of free oxygen increased, most of the anaerobic organisms that had formerly occupied the Earth's surface were probably poisoned by oxygen. But the Great Oxidization Event made possible the eventual evolution of oxygen-based metabolism and life as we know it.