Which of these was the earliest form of heating?

The earliest form of heating (about 1.5 million years ago) was a campfire, around which ancient humans gathered for warmth and cooking. The fire slowly moved indoors with a central fire and a central roof opening for smoke to escape. Heating today has become as simple a process as flipping a switch, setting the temperature, and enjoying the benefits of a warm, welcoming ambiance. But things weren’t as easy for our forefathers who braved and battled winters with whatever was available to them.

Source: QS Supplies