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Scientists have been debating whether climate change or increased human activity led to the extinction of many large animal species more than 10,000 years ago.

Now, a detailed analysis of animal remains and sediment cores in Southern California is suggesting that it was neither just climate change, nor only early humans that led to the extinction – it was both, according to Smithsonian Magazine.

A research team studied fossils collected from the naturally occurring La Brea tar pits, which have been collecting the well-preserved bones of many mammal and bird species for millennia.

The team dated 172 samples from eight different animal species, including saber-tooth cats and dire wolves, in order to trace the timeline of these extinctions. What stood out was that around 13,000 years ago, a range of species suddenly disappeared: With the exception of still-living coyotes, animals such as camels and sloths vanished from parts of the Earth.

The researchers then compared these findings with sediment cores from Lake Elsinore to determine how vegetation was impacted by fires and the changing climate over time.

They noticed an increase in charcoal residue in these cores, which indicates a rise in fire activity – most probably human-caused – nearly 13,200 years ago. At the same time, the climate during this period was also undergoing significant changes, with temperatures increasing and drought conditions prevailing in the area.

This resulted in drastic changes in local plant life: Trees such as oak and juniper disappeared and were replaced by vegetation better suited to fire-prone environments, such as pines and chaparral plants.

The study highlights that species extinctions rarely have a single, isolated cause, but result from a combination of factors.

The findings have broader implications, particularly for the present-day world, which scientists say is experiencing rapid climate change and the far-reaching consequences of human activity.

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