The original fire was actually a wildfire caused by lightning bombardment of the forest. Many wild animals had no time to escape and were burned alive. Primitive people picked up this charred beast and tasted it, and found that it tasted far better than raw food, which was also a reason for promoting primitive people to use fire. However, it is rare for lightning to bombard the mountains in a hundred years. So how to keep the fire going becomes a big problem, so in order to ensure that the fire will not go out, primitive people will assign special personnel to look after the fire, and they will continue to add fuel to the fire to ensure that the fire will never go out.
But it needs a lot of fuel, and some people need to cut firewood from the mountain to join in the fun. Therefore, people who guard the fire should also save some money to ensure the minimum burning of the fire. But sometimes it rains for several days, and primitive people can't continue to go up the mountain to cut wood and make a fire. So that the fire can't continue to burn after the raw materials are used up. Later, primitive people found that burying a burning firewood in the ash pile can ensure that the fire will not go out. However, this method is also unstable. Sometimes it will be buried for too long or in the wrong way, which will also lead to fire extinction.
So later, primitive people found that drilling wood to make a fire was to drill one dry wood on another, and the friction temperature between the two firewood kept rising, eventually producing a flame. Later, primitive people discovered that when two stones collide, they will also produce Mars, which will lead to fire. So later, flint and flint knife were invented.