When something is heated up the molecules within vibrate at a faster and faster rate until it softens, melts and burns. Sound can be used to achieve the same effect. Some new experiments with sound frequencies are focused on levitating objects. Crystals, when pressure is applied, release electromagnetic radiation and sound frequencies that can travel great distances and penetrate stone very easily. So when Joshua blew his horn the walls came tumbling down. And the ancient Incan whistled their walls into place.
My point is combustion is a gross form of energy, there are many subtle ones that pre-historic civilizations may have used instead.
I AM AN IMMORTAL, I LIVE FOREVER
i am anim(mort)al, i die today.
When gravity gets you down, brighten up and
Make light of the grave!