The Washington PostDemocracy Dies in Darkness

Googling for oldest structure in the Americas leads to heaps of debate

Two gentle slopes on the campus of Louisiana State University are recognized as some of the oldest human-made structures in the Americas, though their exact age is up for debate. (LSU Office of Communications and University Relations)
13 min

These days, a black chain-link fence some six feet tall surrounds a pair of gently sloping grass-covered mounds on the main campus of Louisiana State University in Baton Rouge. A newly installed placard zip-tied to the fence provides curious passersby with some context:

“The mounds are the oldest known human-made earthworks in the Americas. Recent studies now estimate that the mounds could be up to 11,300 years old, updating previous studies that estimated they were built 6,000 years ago.”

For visitors tempted to fact check that superlative, a quick search on Google seems to verify the claim. What’s known as a featured snippet appears at the top of the page, summarizing results from a June 2022 study in the American Journal of Science, followed by links dominated by news stories about the paper’s findings.

But ask an archaeologist, and they’ll probably tell you the answer is not so simple.

For months, the straightforward way in which Google has answered this query has deepened a rift in an academic field that already had an uneasy relationship with definitive claims. For professional archaeologists, the burden of proof for a major discovery is staggeringly high, in part because of the difficulty in interpreting artifacts that have been weathered, broken apart and scattered over the centuries.

A Google spokesperson explained that snippets pull information from high-quality sources, and in the case of the LSU mounds, the featured snippet points to a news article from an established source that highlights the scientific study. What’s missing from the snippet is that several archaeologists have questioned the study’s interpretations.

The ongoing, if mostly unseen, debate is the latest chapter in the story of North America’s earthen mounds, which offers a cautionary tale about the historical challenges of walking back established narratives. It’s also a case study of the process by which scientific discoveries — confirmed or not — become popularly accepted as fact in the modern era of rapid communication dominated by search algorithms and a superabundance of information, not all of which is reliable and complete.

An enduring mystery

Around the same time that the ink was drying on the U.S. Constitution, settlers moving west into the Ohio and Mississippi valleys were encountering curious aspects of the landscape: mounds, platforms and embankments that had been clearly sculpted by human hands. Although such structures had been documented centuries before — notably by Hernando de Soto in the mid-1500s — reports of enormous earthen works on the western frontier captivated the public imagination.

The lack of immediately available information gave European settlers license to dream big. In the regular contours and angles of these land masses, they saw the work of a great civilization on par with the ancient Romans, a fitting forebear to the young nation. Theories about their origin abounded, ranging from Welsh or Hindu explorers, survivors of Atlantis, members of de Soto’s expedition and the Lost Tribes of Israel.

What was clear was this: The settlers were unwilling to believe that the Native American population, which had been all but decimated by Manifest Destiny’s westward expansion, could have constructed such structures.

It wasn’t until 1894 that the Smithsonian Institution released an official report stating unequivocally that Native Americans had built the mounds, reversing its previous claim from 1848 that the earthen works were the product of an “extinct race, whose name is lost to tradition itself.” Most professional archaeologists accepted the conclusion, but skeptics remained among the general population.

“In the Americas, Indigenous people were dehumanized from the very start of colonization,” said Indigenous archaeologist Paulette Steeves of Algoma University in Canada. “That carried through into anthropology in the early 1900s, when they didn't even believe that the Indigenous people had built the mounds.”

As the field of archaeology continued to develop — often without the input of the Indigenous populations that experts sought to understand — a picture of the people who had constructed the mounds began to emerge. Experts now believe these structures played an integral role in the ancient ceremonial landscape, functioning as gathering places to renew community ties and perform ceremonies.

But the question of just how old the structures were persisted.

Notes of caution

So far, more than 700 mound sites have been recorded across Louisiana, although many have since been destroyed by industry, agriculture and developments on private land.

In 1983, archaeologist T.R. Kidder, then 23, made his way through a densely forested area of northeastern Louisiana. Alongside a handful of other scholars, he mapped 11 earthen structures connected by ridges, which had been revealed by loggers clear-cutting the thick pine forests. Ultimately, the scholars decided that these mounds, at an archaeological site called Watson Brake, weren’t as historically significant as they might have hoped.

“I didn't see them for what they are,” Kidder said. “And so we — I don't want to say wrote them off — but we never did any further investigation.”

Around the same time, radiocarbon dates for a number of mound sites throughout the southeastern United States were coming in far older than expected. In some cases, mounds were being dated to the Middle Archaic, or 6000 to 2000 B.C. Still, archaeologists weren’t exactly screaming “Eureka!” from the rooftops.

Some hesitated to publish. Others attached “notes of caution” to their work when they did. But as more work was conducted — and as soil scientists, geologists and other academics began to work across disciplinary lines — the puzzle began to come together.

In 1993, archaeologist Joe Saunders visited Watson Brake and took core samples of the tallest mound. Four years later, Saunders and a multidisciplinary list of co-authors published their findings in the journal Science. They dated the mounds at nearly 3400 B.C., pushing the tradition of mound-building back nearly 2,000 years.

“Science was doing exactly what it was supposed to do: challenging what we see, asking, ‘Is it correct?’ and, when it wasn't, ultimately self-correcting,” Kidder said.

The slow unfolding of the mounds’ most reliable age shows how archaeologists generally hew closely to the aphorism popularized by Carl Sagan: Extraordinary claims require extraordinary evidence.

Google search results, on the other hand, often do not.

The trouble with superlatives

​​"So, right now, when I Google ‘oldest man-made structure in America,’ the top result is LSU Campus Mounds from the Louisiana Eliminator,” said Filippo Menczer, a professor of informatics and computer science at Indiana University.

“That is highlighted as a snippet, which is using their semantic search. And so it shows the title, it shows a snippet of text, and it shows some pictures, right? So that means … Google has determined that this is a factoid — a fact.”

The snippet information is largely pulled from a news release LSU sent out on Aug. 19, 2022. In the days that followed, the study circulated through local, national and international outlets, from Gizmodo to the U.K.’s Daily Mail, all of them touting variations of the same headline.

“These kinds of, let’s say, news — the biggest, the oldest, the most beautiful, whatever it is — they have novelty. People naturally tend to pay more attention to things that are novel,” Menczer said. And because attention is a form of currency on the internet, search algorithms incentivize news outlets to embrace superlatives and declarative statements.

Whenever a great deal of attention is brought to a given subject, Google pushes it higher in the search results, Menczer explained. Over time, as Google gathers more evidence and data, the rankings may drop — especially if the sources providing the search results are news outlets, because recency is key for the algorithm.

Google spokesman Ned Adriance noted that the company is constantly updating its search algorithm to improve the quality of its answers. “For example, we recently improved featured snippets so they better reflect consensus across a range of sources, and we’ll continue to make improvements to ensure snippets are helpful, reliable and relevant,” he said.

Not long after, at the company’s annual flagship event in May, Google announced it would be using generative AI to “supercharge” its search function.

In an early version of Google’s Search Generative Experience, the AI is still unequivocal in its answer: “The LSU Campus Mounds are the oldest known and intact man-made structures in the Americas. Radiocarbon dating indicates that construction began about 11,000 years ago.” But the AI answer also acknowledges that Watson Brake is the “oldest reliably dated human-made structure in North America.”

What is glaringly absent from any form of search result is a mention that the claim, though published in a peer-reviewed journal, had failed to win over the archaeological community.

Answers in the ash

The heart of the controversy goes well below the surface, to the bands of gray material at the base of the LSU Campus Mounds.

In their paper, which is based on 31 radiocarbon dated samples, Brooks Ellwood, a professor emeritus of geology and geophysics at LSU, and his co-authors proposed that this layer is made of “many thin, burned ash lenses, suggesting that the Mounds may have been used for ceremonial or cremation purposes.” In one of the mounds, they said, the burned reed and cane materials they found can be traced back nearly 11,000 years.

If true, this would push back mound-building activities in North America nearly 4,000 years.

Archaeologists, however, weren’t convinced that the ash layer was ash at all, or that it indicated intentional human activity. Thickets of grasses and reeds known as cane breaks are found across the Southeast in lowland areas prone to flooding, and periodic burning is part of their life cycle. It’s possible the mound-builders carried soil mixed with centuries’ worth of burned reeds up to higher ground, which means the materials found in the white sediment could be much older than the mound construction.

In an hour-long podcast episode last September, archaeologists Shane Miller and Jesse Tune noted a number of red flags in the LSU study, ranging from the need for more data about the sediments to questions of standard practice and procedure. They also noted that none of the paper co-authors is an archaeologist, and that the American Journal of Science is focused on geology and earth science, not archaeology.

A more formal rebuttal came a few months later. In November 2022, a group of LSU archaeologists published a paper in the SAA Archaeological Record, a bulletin of the Society for American Archaeology, that analyzed the evidence for the dates of the mound material and the tempo of construction. Their main argument is that, while the ages of the canebrake layers may be accurate, there’s no way to know for sure when that material was placed at the site.

“We wish to be clear we do not dispute the accuracy of the data, including the dates, presented in the published article by Ellwood and colleagues,” the authors write. “Rather our concern is with the interpretations generated from that data.”

LSU archaeologist Rebecca Saunders says she declined Ellwood’s offer to co-author the LSU Campus Mounds paper. Instead, she co-authored the rebuttal.

She acknowledges their paper was published quickly by academic standards but said it was done in the interest of time, to get the word out to other experts that the revised dates are contentious.

“We published in that [bulletin] because it was fast — relatively fast — hoping we could nip this in the bud, as opposed to the year-and-a-half to two years it would take to compose something that would be acceptable to a national journal and get it all through [the] review process,” Saunders said.

Ellwood countered that the rebuttal paper was not “rigorously reviewed,” and he and his team stand by their conclusions. Debate about the mounds’ age continues among academics, and the consensus appears to be that science will work things out eventually as more lines of evidence emerge.

But more than year after Ellwood’s paper was published, the snippet answer remains.

Preserving the mounds

On the informational sign outside the LSU Campus Mounds, there’s a second paragraph, and this part isn’t open to debate:

“Because of their age, the mounds are at risk of deterioration. Scientists have found that one of the mounds has an unstable interior due to its watery soil composition, and both are susceptible to erosion and vibrations from nearby streets. We must take steps to preserve these archaeological treasures and limit the factors that may cause damage.”

The past several years have seen more attention paid to preservation than at any time since the university purchased the Gartness Plantation, the site of the mounds, in 1918. Steeves, the Algoma University archaeologist, argues that the people studying and preserving earthen mounds around the country also need to do more work to build relationships with Indigenous communities.

“It flows from them to education and to the general public, the worldviews that are built about Indigenous people,” she said.

In a statement, LSU acknowledged the university’s role as a “modern steward” in the mounds’ preservation, and stated that it supports and encourages continued investigation into these historic structures. It did not address whether there were any plans to change the plaques.

Recently, LSU’s Saunders said she sat on a campuswide committee to apply for $1.75 million in federal funds from the National Park Service that would help stabilize the mounds and educate the public. Although she still has strong feelings concerning the interpretation of Ellwood’s dates, she admits the intense news coverage had a silver lining.

“I think that it’s got a shot,” Saunders said of the grant. “And that 11,000-year-old business can’t hurt, and likely helps.”