Extreme drought unearthed a human skull in the Minnesota River. A forensic anthropologist says it may be 8,000 years old.

• Kayakers stumbled upon a human skull along the Minnesota River during a drought last September.
• A forensic anthropologist's report estimates the skull could date back 8,000 years, local officials said.

Last year, a pair of kayakers stumbled upon a human skull along the drought-stricken Minnesota River during the last days of summer. Experts say it could belong to a man who lived 8,000 years ago.

On Wednesday, Renville County officials said the two kayakers reported finding a brownish chunk of skull while coursing along the Minnesota River, according to The Washington Post. They came across the skull in September during a drought, which prompted low water levels in lakes and rivers across the state. Officials said they first treated the discovery as a possible crime, suspecting it might be the remains of a person who recently died.

They sent the bone fragment to an FBI forensic anthropologist in the hopes of pinpointing its origin. The anthropologist used carbon dating to calculate its age, a technique that hinges on the fact that all living things absorb radioactive carbon from the atmosphere and food sources. When living things die, the carbon that they've accumulated decays in a predictable pattern, allowing researchers to estimate how long that plant or animal has been dead. Ultimately, the anthropologist estimated that the skull belonged to a young man who lived as many as 8,000 years ago, between 5,500 and 6,000 BC.

"To say we were taken back is an understatement," Scott Hable, Renville County sheriff, told The Washington Post, adding, "None of us were prepared for that." The Renville County Sheriff's Office did not immediately respond to Insider's request for comment.

The anthropologist's findings also suggest the man's diet was heavy in fish, or that he ate considerable amounts of maize, pearl millet, or sorghum, long before conventional agricultural and farming methods were invented, according to CBS Minneapolis affiliate WCCO. A depressed area on the skull fragment suggests he may have suffered blunt force trauma.

"The available science and technology are truly incredible, and we are fortunate to have the partners that we do to assist us in this investigation and to have come across this little piece of history," the sheriff's office said in a statement, according to WCCO.

The announcement and pictures of the skull, shared on the sheriff's office Facebook page, caused upset in Minnesota's Native American community. Dylan Goetsch, a cultural resources specialist with the Minnesota Indian Affairs Council, said in a statement that it was "unacceptable and offensive" for tribes to learn of the skull through Facebook, according to Minnesota news organization MPR News. (The social media post from the sheriff's office has since been taken down.)

The announcement comes as more modern human remains have been unearthed by receding water levels at Nevada's Lake Mead — the country's largest reservoir. Earlier this month, lake visitors found the remains of a person, who had been killed about four decades ago, in a rusty barrel.

A growing body of research has linked climate change with longer and more severe droughts. Beyond receding water levels, melting ice and snow caused by warmer temperatures are also revealing bodies buried for decades, Jennifer Byrnes, a forensic anthropologist who consults with the Clark County, Nevada, coroner's office, told Insider earlier this month.

"I would expect human remains of missing persons will probably be revealed over time, as the water level continues to recede," Byrnes said.

Less than a week after the body in a barrel was reported at Lake Mead, additional human remains were found along the water's edge.