13,000 years ago, the rich and thriving megafauna of Southern California came to an abrupt halt. If the cause of this extinction has long remained controversial, a new study has revealed new elements that also call into question man and his still very uncertain control over fire.
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Bison, ground sloths, horses, saber-toothed tigers, camels… many emblematic animals of the late Pleistocene that populated vast swaths of Southern California. Today, this wild landscape is submerged under the asphalt of downtown Los Angeles. But right in the heart of the city, 5801 Wilshire Boulevard In fact, a preserved collection of this megafauna of the American West still exists. In fact, this is where a surprising deposit of fossils named la bree tar pits, A deposit that has a characteristic. To realize this, it is enough to carefully observe the lake present at that place. Because there is no clear water flowing here, but sticky mud on which you can see some black bubbles bursting.
The fossil-rich asphalt lake that witnessed a bizarre extinction 13,000 years ago
This liquid asphalt lake has been known for a long time and apart from being of interest for its oil resources, the site is of great importance to paleontologists. Because this source of asphalt already existed 15,000 years ago. We are then in the last part of the Ice Age, at the end of the Pleistocene and the region has been extensively surveyed by many mammals, most of them large. Animals that search for water find themselves trapped in these sticky ponds. To the delight of scientists, the asphalt fossilized their remains, preserving them to this day. The La Brea site therefore represents an excellent piece of evidence of this period of Wisconsin glaciation and makes it possible to reconstruct the fauna and flora that lived at that time.
A fairly prosperous and well-established megafauna, which, however, came to an abrupt end 13,000 years ago. Why ?
hot, dry environment conducive to fire
So far, scientists have pointed to two possible causes: humans and climate change. A new study published in the journal Science, comes with a hyphen to join the two: fire. This new hypothesis arose precisely from the analysis of fossils found at the site of La Brea. Furthermore, it has surprising resonance with the current situation. Because for the researchers, these large mammals from the last Ice Age may have died out suddenly due to global warming and the introduction of fire use by human communities living in the region.
Dating of bones found at the site of La Brea allows researchers to realize a sudden decline in biodiversity around 13,000 years ago. While the previous period is marked by the presence of many different species including bison and saber-toothed tigers, the following period is marked by the presence of only coyote bones. To understand what really happened, the researchers went to sample the bottom of another lake, this time composed of fresh water. And the analysis of sediments made it possible to reveal in detail the sequence of events.
The person responsible for the fierce forest fire
Analysis of the nature of the pollen and sediments suggests that 14,000 years ago, the global climate was significantly warmer and drier. In Southern California, temperatures have risen by 5.6 °C over a few thousand years. Thus dry vegetation would have become more vulnerable to wildfires. Nothing dramatic yet. But that was without counting on the arrival of a new actor: Man. Lake sediments indicate a huge increase in coal deposits 13,200 years ago, apparently indicating an unprecedented increase in destructive fires. A situation that persisted for several hundred years. This date coincides surprisingly well with the arrival of the first human communities in the region, whose mastery over fire was then only rudimentary. Although playing with fire in dry grass environments can lead to disasters, we still know a little about it today! Except that at that time our ancestors had no means of extinguishing fire.
The fire would have devastated the region, destroying the habitats of many species and causing the extinction of most large mammals of the time.
The authors emphasize the fact that it only took 200 years for humans to fundamentally change the landscape of Southern California and reset the local ecosystem’s counters. Some 13,000 years later, we are again in the same scenario.
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