The big fire.

Amazing, huh?

I always think it's interesting to consider that petroleum oil comes from organic plant matter that was alive hundreds of millions of years ago. And interesting to think about the solar energy that gave that plant matter life, locked up since then in carbon-carbon and carbon-hydrogen chemical bonds, free now to energize my computer, fuel my car, or burn down freeways in California.

Then, take another step back and think about the plant progenitors that first put the flammable molecular oxygen necessary to burn that fuel in the atmosphere to begin with...