The mounds were once ceremonial pyres, although it’s unclear if they were used to incinerate humans or animals.
According to recent findings published in the American Journal of Science, two six-meter (20-foot) high mounds on the campus of Louisiana State University (LSU) are the oldest man-made structures yet found in North America. The construction of the mounds began some 11,000 years ago, and according to radiocarbon dating, it was finished over several millennia.
The two LSU Campus Mounds were built up in stages, the oldest of which contained ash from burned reeds and cane plants, according to an analysis of sediment cores recovered from the mounds. The scientists discovered osteons, tiny bits of burned mammal bones, within this ash.
The authors state that the layers of cane and reed phytoliths, which have very few osteons, are a sign of intense fires. Such infernos would have been too hot for cooking, therefore they probably had a ceremonial purpose. The researchers go on to say that their discovery “supports the hypothesis that the fires were utilized for ceremonials or cremations.”
Unfortunately, the team was unable to establish whether the osteons were animal- or human-derived. The Native American tribal communities that were contacted reportedly declined their request for authorization to conduct DNA tests on the microscopic bone particles recovered.
The two hillocks, known as Mound A and Mound B, were not fully constructed until about 6,000 years ago. They were built by ancient Indigenous people.
The buildings are aligned with a point on the horizon that is 8.5 degrees east of true north, according to the researchers. The red giant star Arcturus, one of the brightest lights in the sky, would have risen at this same moment six millennia ago.
Author of the study Brooks Ellwood commented on this result in a statement, saying that “the people who built the mounds, at roughly 6,000 years ago, coordinated the orientation of the buildings to line with Arcturus, seen in the night sky at that time.”
The researchers used their findings to recreate the histories of the two mounds, finding that Mound B was built around 11,000 years ago and Mound A around 9,500. But based on the arrangement of tree roots inside the mounds, it appears that they were abandoned for nearly a thousand years, starting around 8,200 years ago, when the northern hemisphere saw a sharp and sudden drop in temperature.
According to Ellwood, “We don’t know why they left the mounds around 8,200 years ago, but we do know that their environment altered abruptly and significantly, which may have affected many elements of their everyday lives.”
The two knolls were nearly half their present height when construction eventually resumed some 7,500 years ago. The two mounds were gradually increased in size over the following 1,500 years, at which point “the LSU Campus Mounds were abandoned by the Indigenous people for good.”
The authors claim that the LSU Campus Mounds may be the earliest known and still-intact man-made structures on Earth since the two little hills have endured the test of time despite being abandoned.
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