Short answers, pulled from the story.
Fire first appeared on Earth during the Middle Ordovician period approximately 420 million years ago. The earliest physical evidence of this phenomenon appears in the Late Silurian fossil record dated to 419 million years ago where fossils of charred plants provide proof of fire.
Evidence of occasional cooked food dates back to 1.5 million years ago suggesting that fire was used in a controlled fashion during this period. Other sources place the date of regular use at 400,000 years ago with widespread evidence appearing between 50,000 and 100,000 years ago.
Fire cannot exist without all of these elements in place and in the right proportions: fuel oxygen heat and a chemical chain reaction. A flammable liquid will start burning only if the fuel and oxygen are in the right proportions and a chain reaction must take place whereby fires can sustain their own heat.
The period of history characterized by the influence of human-caused fire activity on Earth has been dubbed the pyrocene. Globally today as much as 5 million square kilometres an area more than half the size of the United States burns in a given year.
The earliest modern flamethrowers were used by infantry in the First World War first used by German troops against entrenched French troops near Verdun in February 1915. They were later successfully mounted on armoured vehicles in the Second World War.
The religion of Zoroastrianism is closely linked to this practice viewing fire as a sacred component. The fire in a hearth was perceived as symbolic of the Heavenly Fire and thus is considered a sacred component by fire worshipping cultures.