How taming fire made us human

"Then you need oxygen. There are no fires without a lot of oxygen in the air, so, as a result, there weren't fires for most of Earth history. Though oxygen is the by-product of making plant matter from CO 2 through photosynthesis, to build oxygen up to appreciable levels, vast seas of this organic carbon have to be buried in the crust as fossil fuels."

"Every breath you take is the gift, not of plant life today, as the intuitive cliché goes, but rather the impounding of some small fraction of this life in the crust, leaving behind an oxygen surplus that has taken hundreds of millions of years to accrue. And fire on the surface doesn't catch until oxygen reaches about 16% of the atmosphere."

Fire has been present on Earth for roughly 430 million years, a small fraction of planetary history. Lightning has provided the dominant natural spark throughout the history of fire, though human-set fires now outnumber natural ignitions. Atmospheric oxygen must reach high levels before surface fires can sustain; oxygen accumulation required burial of vast amounts of organic carbon as fossil fuels. The oxygen surplus enabling modern fires took hundreds of millions of years to accrue. Surface fire only becomes common once oxygen reaches roughly 16% of the atmosphere, alongside sufficient combustible material.

Read at Big Think