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Blue lake and red tundra in Noatak National Preserve/NPS

Biomarkers In Ancient Alaskan Lake Sediment Could Influence Thinking About Early Beringian Migration

By Max Graham, Shared Beringian Heritage Intern

A group of Brown University researchers, funded by the Shared Beringian Heritage Program, is tracking evidence that supports a new but disputed theory about when and how human beings first arrived on the American continent. Brown professor Yongsong Huang and his team of researchers believe they have found traces of human fecal matter and fire activity in northern Alaska dating back more than 30,000 years—thousands of years before the archaeological record indicates humans were in Alaska. Although the results of his lab’s latest work—an analysis of sediment dating to as long ago as 200,000 years—have not been published yet, Dr. Huang’s research over the last five years has contributed significant new data to the contentious debate over the peopling of the Americas via Beringia, a landmass that spanned Siberia and Alaska during the last Ice Age.

For several decades, archaeologists and scientists have surmised that humans first arrived in North America from Asia nearly 15,000 years ago, at the end of the Last Glacial Period, Earth’s most recent Ice Age. The conventional theory holds that ancient human hunters crossed over the Bering Land Bridge, following mammoth across a grassland steppe now submerged under the Bering Strait. Once across the land bridge, most archaeologists believe, the first Americans steadily moved south and over time diverged into the many indigenous communities from the Canadian Arctic to the southern tip of Chile.

But researchers are not exactly sure when a migration, or series of migrations, took place, and for how long. Archaeological findings in Siberia indicate human presence about 45,000 years ago. But the only undisputed physical evidence in North America marks human habitation much later, about 14,500 years ago.

Still, some researchers think humans might have inhabited Eastern Beringia during the Last Glacial Period, isolated from the rest of North America by a massive ice sheet. According to recent analyses, cut-marked horse and mammoth bones found in the 1980s and 1990s at the Bluefish Caves, in the Yukon Territory, likely date back about 25,000 years, directly contradicting the conventional theory of a “swift peopling” of North America, although other researchers question the age of the Bluefish Cave evidence and whether the bones were in fact modified by people. DNA analyses support the notion that the genetic makeup of modern Native Americans evolved from a long-isolated Beringian population, and climatological data suggest that ancient Beringia was more hospitable to human life than many parts of Siberia.  While archaeologists, geneticists, climatologists, and biochemists debate the varying data that bear on what we know about the earliest Beringians, some uncertainty remains regarding how and when Homo sapiens came to the Americas.

Over the last few decades, a new theory has formed, called the Beringian Standstill Hypothesis (BSH). According to the BSH, the Bering Land Bridge wasn’t just a bridge, but part of a landscape that humans long inhabited. Perhaps humans populated Beringia, ranging from northeastern Siberia to northwestern Canada, for thousands of years, during the Last Glacial Maximum (about 25,000 BCE) and before moving south into the Americas. Rather than, or in addition to, a swift movement into North America, an isolated human population might have settled in Beringia, diverging genetically and culturally from their Eurasian ancestors.

In 2018, the Shared Beringian Heritage Program funded the researchers from Brown to trace the Beringian Standstill Hypothesis using organic geochemistry. The group analyzed lake sediment cores, searching for chemical evidence of human fecal matter and fire during and even before the last Ice Age.  

The researchers, led by Dr. Huang, retrieved samples from three maars—lakes formed in volcanic craters, up to 200,000 years old—on the Seward Peninsula, in northwestern Alaska. Their goal is to see how far back they can find evidence of human feces and fire activity.

This project was inspired by discoveries they made a few years earlier on Alaska’s North Slope. Dr. Richard Vachula, who recently earned his PhD from Brown, began his graduate studies working with Dr. Huang on a sediment core from Lake E5, just off the Dalton Highway about 100 miles north of Wiseman. The Lake E5 samples were as old as 30,000 years and contained a record of Beringia’s climate and ecology through the Last Glacial Maximum. No one yet had published a biomarker analysis of Beringian sediment of that age. “This E5 record was really valuable in that it went back three times longer than most previously published records,” Dr. Vachula said.

Dr. Huang and Dr. Vachula are chemists, and their original research question was related not to human migration but to the climate. “At first we weren’t thinking of the human story,” Dr. Huang said.

After the Anaktuvuk River fire, a rare wildfire on the North Slope in 2007, the researchers wanted to see if there were traces of charcoal—evidence of fire—in the region during the last Ice Age, when the climate was much colder. The cold should not be a factor in increased fire presence, so Dr. Huang expected that there wouldn’t be much if any evidence of fire in the geological record of the Last Glacial Maximum.

But to Dr. Huang’s “total surprise,” there was. “You’re talking about a lot of fire in this area,” Dr. Huang said. 

“It was a bit confusing,” Dr. Vachula said, “because when we think about fire in the tundra, we think that warmer, dryer climates are going to produce more fire, and what we found was there was more fire in a cold and relatively dry climate.”

So, Dr. Vachula wondered, “Why was there all of this burning in the Last Glacial Period?”

The researchers’ hypothesis was that humans promoted the burning. “Usually if you find fire in an ignition-limited system, which is what the North Slope is…you would point to that in paleoecological records and say it was probably humans lighting these fires.” Dr. Vachula then analyzed the Lake E5 core for another biomarker, linked to human feces. He found it all the way through the core’s oldest layer: “pretty convincing evidence” of human fecal matter from about 32,000 years ago, according to Dr. Vachula. “What we found was a smoking gun of fecal contamination of the sediment indicative of human presence, as well as fire in an area where there shouldn’t have been.”

After the Lake E5 study, Dr. Vachula and his colleagues analyzed a similar sedimentary record from Burial Lake, in Alaska’s Noatak National Preserve, and found the same biomarkers of fire and human feces. “These analyses support the presence of humans in Beringia during the Last Glacial and suggest that they promoted fire activity,” Dr. Vachula, Dr. Huang, and their colleagues wrote in a 2019 paper titled “Sedimentary biomarkers reaffirm human impacts on northern Beringian ecosystems during the Last Glacial Period.”

With biomarkers likely evident of human life in Eastern Beringia during the Last Glacial Maximum, Dr. Huang and Dr. Vachula set their sights on the second-to-last glacial maximum, about 150,000 years ago, when there almost certainly were no humans in Beringia. The team turned their attention to the maars on the Seward Peninsula, some of Beringia’s oldest lakes.

If the researchers find no evidence of fire in the previous glacial maximum, then they might have stronger reason to believe that the evidence of fire about 32,000 years ago indeed can be linked to human activity, although there still would be no indication that those humans comprised the “standstill” population. If they do find fire evidence in the previous glacial, “then the ecological theories are wrong,” Dr. Huang said, referring to the theories that a colder climate would mitigate fire presence.

Conclusive results from the Seward Peninsula samples will not be published for several months, but no matter what the team ultimately finds, their research will contribute to our understanding of ancient Beringia’s climate and to the debate about human arrival in North America.

Still, as Dr. Vachula said, “The question of when humans arrived in Beringia can’t be answered with one approach.” Despite Dr. Huang, Dr. Vachula, and their colleagues’ work, serious questions about Beringian human history will remain, and the lack of unequivocal archaeological evidence will continue to generate skepticism about theories rooted in genetics or biochemistry.