Fire is the oxidation of a combustible material releasing heat, light, and various reaction products such as carbon dioxide and water. Archaeology indicates that humans might have controlled fire as early as 790,000 years ago.
The control of fire by early humans was a turning point in human cultural evolution that allowed for humans to proliferate due to the incorporation of cooked proteins and carbohydrates, expansion of human activity into the night hours, and protection from predators.
One of the primary changes to the behavior of humans due to the control of fire was the utilization of the light. With the light from fires, activity was no longer restricted to the daytime. In addition, animals in general avoid fire and smoke. Another change that fire provided was the opening of the nutrition in cooked proteins.
The cooking of plant foods may have triggered brain expansion by allowing complex carbohydrates in starchy foods to become more digestible and allow humans to absorb more calories. Because of the indigestible components of plants such as raw cellulose and starch, certain parts of the plant such as stems, mature leaves, enlarged roots, and tubers would not have been part of the hominid diet prior to the advent of fire.
Instead, the diet consisted of the parts of the plants that were made of simpler sugars and carbohydrates such as seeds, flowers, and fleshy fruits. The incorporation of toxins in the seeds and similar carbohydrate sources also affected the diet, as cyanogenic glycosides such as those found in linseed, cassava, and manioc are made nontoxic through cooking.
The use of fire profoundly altered the landscape. Intentional burning of vegetation was taken up to mimic the effects of natural fires that tended to clear forest understories, thereby making travel easier and facilitating the growth of herbs and berry producing plants that were important for both food and medicines.
It is believed that the earliest pottery was hand built and fired in bonfires. Firing times were short but the peak temperatures achieved in the fire were high. Clays tempered with sand, grit, crushed shell or crushed pottery were often used to make ceramics, because they provided an open body texture that allows water and other volatile components of the clay to escape freely.
The first technical application of the fire may have been the extracting and treating of metals. There are numerous modern applications of fire. In its broadest sense, fire is used by nearly every human being on earth in a controlled setting every day. Users of internal combustion vehicles employ fire every time they drive. Thermal power stations provide electricity for a large percentage of humanity.