One of the earliest forms of use of fire in prehistoric times was called a "bowl of fire" a kind of hole dug into the ground.
Then the "hearth" was raised with stones placed in a circle around the hole. Later it was further raised with earth and stones.
Only later the hearth was circumscribed with a "wall" thus becoming safer inside the houses and improving the way food is cooked.
Weathered wood and combustion
Wood seasoning is a fundamental process because as soon as it is cut it has a high moisture content, around 60% of its weight, therefore of water.
For a better yield it is necessary to reduce this humidity through the seasoning, which can last either an entire summer (humidity decreases up to 25%) or even two years (moisture content even of 15-20%) optimal value to be able to use it for energy purposes.
During combustion, a certain amount of energy is released in the chemical bonds between the substances that make up the wood, if there is a lot of humidity inside the wood in combustion, a large part of this energy is used to evaporate the 'water and not to provide heating.