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Humans were altering ecosystems with fire some 92,000 years ago

Excavations near Lake Malawi in eastern Africa yielded dense clusters of stone artifacts dating as far back as 92,000 years ago, suggesting humans used fire to control their environment at the time. Photo by Yale University
Excavations near Lake Malawi in eastern Africa yielded dense clusters of stone artifacts dating as far back as 92,000 years ago, suggesting humans used fire to control their environment at the time. Photo by Yale University

May 5 (UPI) -- Humans living along the northern shores of East Africa's Lake Malawi were altering the local ecosystem with fire as early as 92,000 years ago, according to a new study.

Analysis of stone artifacts and paleoenvironmental data -- detailed Wednesday in the journal Science Advances -- suggests fire use by early humans prevented regrowth of the region's forests, yielding the expansive bushland that persists today.

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"This is the earliest evidence I have seen of humans fundamentally transforming their ecosystem with fire," lead author Jessica Thompson said in a press release.

"It suggests that by the Late Pleistocene, humans were learning to use fire in truly novel ways. In this case, their burning caused replacement of the region's forests with the open woodlands you see today," said Thompson, an assistant professor anthropology at Yale University.

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Scientists were able to discern the impacts of human behavior on local ecosystems by analyzing both stone artifacts and sediment cores collected from dig sites across the lake's alluvial fan, as well as from the bottom of Lake Malawi.

Field observations revealed several unique patterns, including increases in sedimentation and charcoal accumulation some 92,000 years ago.

Researchers found that shortly after the first spike in charcoal accumulation, pollen signatures revealed a flattening of the region's species diversity.

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"The pollen that we see in this most recent period of stable climate is very different than before," said co-author Sarah Ivory, assistant professor of geosciences at Penn State.

"Specifically, trees that indicate dense, structurally complex forest canopies are no longer common and are replaced by pollen from plants that deal well with frequent fire and disturbance," Ivory said.

What at first looked like distinct archaeological and climate patterns started to appear interconnected, the researchers said.

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Around the same time that the region's forests were disappearing and a large alluvial fan first formed along Lake Malawi's northern shores, scientists noted a proliferation of archeological sites.

Fire use by early human populations in the region not only helped transform the region's ecosystem, but also ensured the preservation of thousands of artifacts from the Middle Stone Age.

"Dirt rolls downhill unless there is something to stop it," said co-author David Wright, an archaeologist at the University of Oslo. "Take the trees away, and when it rains, there is a lot of dirt moving downhill in this environment."

Researchers aren't sure why these early human groups were burning so much land. In addition to burning fuel for warmth and cooking, it's possible hunter-gatherers in the region were using controlled burns to create open landscapes more conducive to hunting.

What is clear, however, is that these weren't forest fires.

"One way or another, it's caused by human activity," Thompson said. "It shows early people, over a long period of time, took control over their environment rather than being controlled by it. They changed entire landscapes, and for better or for worse that relationship with our environments continues today."

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