Anything that burns was once alive.
I grew up in an area where wildfires were common. The fires sent pillars of smoke into the sky. The smoke would spread out and begin a slow procession overhead. The sun shining through the pall turned the world orange, brown, or gray. Some times, there would be ashfall.
The smoke overhead, and the ash that fell on us, was once alive. Wood, grass, the countless microbes that lived on those, and animals.
The tendency for flammable things to be the remains of a living thing extends beyond wildfires. Petroleum, coal, natural gas — those are all things that were living long ago. When I drive my car, the fuel in the tank is made of things that died long before I was born.
This tendency for flammable things to have lived before is because Earth’s life creates volatility.
Water in the soil, and carbon dioxide in the air, do not burn in a normal fire. When lightning strikes dirt, there is no wildfire. But plants combine those non-flammable ingredients into larger, more volatile compounds. Heat those up, and they’ll burn.
Life makes things more complex and precarious. Fire disassembles that complexity into a simpler state.
There are non-living things that can be fiery, like magma in the earth, or tiny flakes of iron that shine as sparks. Humans can make artificial compounds that burn. But, generally, if something is flammable, then life made it that way.
I understand the chemistry of it. But when I look up, and see a smoky sky, it seems to me like a solemn funeral procession.