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Few skills play a more elemental role in the story of humanity’s progress from hunter-gatherer to civilization builder than the mastery of fire. These blazes provided not just warmth and protection against predators, but also a draw for social gatherings, a means of cooking food, a source of light, and a method to forge new tools. Human use of fire eventually became so sweeping that it re-shaped Earth’s ecosystems and began to influence the planet’s climate.
Archaeological remnants suggest human ancestors first began to use fire in a controlled manner around 400,000 years ago, but chronological gaps in the record have made it difficult to determine when their mastery of the conflagration became widespread enough to impact the Earth itself. Some scientists suspected this happened relatively recently, around 11,000 years ago, during the Holocene, when agriculture had already taken root. Now a team of researchers from China, Germany, and France has found evidence in carbon cores that humans came to use fire extensively around 50,000 years ago, during Homo sapiens’ first successful migration out of Africa to Europe, Asia, Southeast Asia, and Australia. This period coincided with rising population densities and cold glacial conditions. The researchers published their findings in PNAS.
The team of scientists, from the Institute of Oceanology of the Chinese Academy of Sciences, together with collaborators from other institutions in China and Europe, analyzed carbon in three 300,000-year-old sediment cores taken from the East China Sea. Around 50,000 years ago, the core showed a doubling in pyrogenic carbon, which persisted over time. Pyrogenic carbon, or charred plant remains, is created when vegetation burns but is not completely consumed by fire. Similar observations have been made in pyrogenic carbon records from the Sulu Sea in the Philippines, the Caroline Basin north of Papua New Guinea, and northeastern Australia.
Taken together, these findings suggest human fire use spread rapidly across the globe and permanently altered the Earth’s carbon cycle well before the last glacial maximum, when vast ice sheets covered portions of North America, Europe, and Asia, according to the team of researchers. Before they had even settled down to work the land and raise crops, our ancestors had likely begun to alter their home planet, increasing carbon dioxide in the atmosphere and changing patterns of temperature and rainfall. The fresh evidence could help us understand how Earth responds to human influence and shift the baseline of human-ecosystem interactions used in most climate modeling today. 
Lead art: Kit8.net / Shutterstock
