One of these high-fire intervals occurred during the later stages of the Cretaceous, when dinosaurs ruled the Earth and flowering plants first appeared. During these times, fires would have been hotter and more frequent. We know that there were also periods through Earth history when oxygen levels in the atmosphere were higher than today. Though plants had spread on land at that point, fluctuating levels of atmospheric oxygen meant that the first extensive wildfires recorded came somewhat later, dating from around 345 million years ago, the early Carboniferous Period. The oldest fire recorded on Earth has been identified from charcoal in rocks formed during the late Silurian Period, around 420 million years ago. This is the partially combusted plant material left after a fire has been extinguished. Our evidence of fire in the fossil record (in deep time, as we often refer to the long geological stretch of time before humans) is based mainly on the occurrence of charcoal. The main sources of ignition before humans appeared were lightning strikes. (It is 21% today.) This is why we smother a fire with a blanket or sand, pump carbon dioxide on it, or even flood it with water to extinguish it - to cut off the oxygen. And vegetation fires can’t occur until the oxygen level in the atmosphere has reached around 15%. We would not expect fire on a barren Earth there must be plant life on land that can provide a fuel source.
And third, there must be a heat or ignition source that allows the fire to begin. Second, oxygen must be available - after all, combustion is essentially an oxidation process that gives off heat and light. Three main components are needed for fire. The exact timing of the discovery and use of fire by humans has been a subject of continuing research, yet perhaps two questions have, until now, received little attention: What was fire on Earth like before humans appeared? And what experience of fire could early humans have had? The use of fire by humans has long been considered as a defining property of intelligence, separating us from other animals. Fire is one of the most important forces on Earth.
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