Humanity’s environmental impact did not start with the bang of agriculture or industrialization but a whisper initiated long ago—one that scientists are finally learning to hear.
New archaeological and paleoenvironmental findings now date human activity that transformed our natural surroundings to more than 80,000 years ago, after early modern humans settled on the northern shores of Lake Malawi at the lower tip of eastern Africa’s Great Rift Valley. These humans dramatically modified the landscape and ecosystem by burning forests to yield a sprawling bushland that remains today, according to a report published on Wednesday in Science Advances.
The finding marks the oldest evidence yet of humans profoundly changing their environment with fire. And it could represent the earliest known case of people deliberately doing so, the researchers hypothesize. “It represents a really powerful cultural capacity to transform the landscape in a way … that will enhance the survival of the people,” says archaeologist Amanuel Beyin of the University of Louisville, who was not involved in the new study.
Lake Malawi is one of the world’s largest lakes today, but it has dramatically fluctuated in size across the ages. In a 2018 study, paleoecologist Sarah Ivory of Pennsylvania State University and her colleagues examined fossils, pollen and minerals in two sediment cores drilled from the lake bed. Their analysis revealed that the lake’s water level and vegetation exhibited a consistent climatic pattern over the past 636,000 years. Dense forests along the lake’s shores typically disappeared during drought periods when the lake ran dry and then returned when it filled up again.
But the pollen records showed an abrupt break from this cycle when the wet period returned about 86,000 years ago. Although the lake level was high again, the shoreline forests just briefly recovered before collapsing. Only some fire-tolerant and hardy species persisted, while grasses became more widespread in the landscape.
When Ivory discussed these data with Yale University paleoanthropologist Jessica Thompson and her colleagues, who were excavating nearby archaeological sites along the northern shores of the lake, an explanation came into focus: human activity. The first known settlements in the area pop up roughly 92,000 years ago, as evidenced by tens of thousands of stone artifacts found by Thompson and others with help from their colleagues in Malawi. Many were tools likely used in hunting and cutting. The researchers observed that the humans’ appearance was followed by a spike in charcoal deposits in the lake cores, suggesting that people started intensively burning the forest just as it was growing back, thereby preventing a full recovery.
Alternative explanations are possible. The charcoal deposits could instead have stemmed from a few fires that spiraled out of control or perhaps from people at that time burning timber for cooking or warmth….