It’s “fire season” again in the American West. Then again, it’s been fire season here on Earth for a very long time now. While we humans have had a profound influence on fire regimes, fire itself predates us by hundreds of millions of years; it appeared on Earth concomitantly with terrestrial plants, which both produced the oxygen necessary for fire and acted as a biomass fuel.
In their “A Burning Story” Juli G. Pausus and Jon E. Keeley review the role of fire in the history of life, with its “strong ecological and evolutionary consequences for biota, including humans.” There is evidence for fire 440 million years ago and charcoal in 400 million-year-old Devonian deposits. The Carboniferous, when oxygen made up 31% of the atmospheric mix (compared with 21% now), would have been fire’s greatest reign before hominids.
Soil and climate have traditionally been seen as the contexts for plant evolution, but new theories add fire to the mix. The ability of plants to sprout after fire, the development of thick barks, and smoke-stimulated germination are three factors discussed by Pausus and Keeley.
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They go on to discuss fire in the pre-industrial human world, going back to our ancestors in eastern Africa around 1.6 million years ago. Their date for the earliest non-controversial evidence of fire out of Africa, in the Near East, is approximately 790,000 years ago. Controlled fire — used in cooking, surviving colder climates, and, ultimately, farming – allowed for a transformation of human life.
Along with stone tools, the controlled use of fire is the most significant technology in human evolution, note Roebroeks, Villa, and Trinkaus. However, the question of when humans started using fire is much debated. They examined the evidence for habitual use of fire in Europe and dated it to 300,000-400,000 years ago, after humans moved into northern latitudes.
The great problem in the evidence is that anthropogenic fire produces the same signs as natural fire from lightning, volcanic activity, and spontaneous combustion: charred bone, charcoal fragments, heated flints and other stones. “Much of the debate on the history of human control of fire relates to the problem of the correct interpretation of possible fire indicators.”
But there’s no longer much debate on the importance of fire to life on earth, human development, and its future in a radically disrupted global climate.