Unearthing ancient artifacts helps scientists fill in the gaps about the ancient peoples who came before us. But the window for those discoveries is rapidly closing in some areas, warn a team of Swedish archaeologists.

Their warning is based on findings at Ageröd, an archaeological site in southern Sweden. Archaeologists excavated the site in the 1940s and then again in the 1970s. Fast forward to 2019, when the Swedish team dug up new artifacts and compared them to those that had been previously excavated. The specimens from 2019 showed extreme weathering and degradation, so the researchers concluded that archaeological remains in the bog have rapidly deteriorated in the past 75 years, likely due to climate change and pollution. And artifacts at other sites may be experiencing the same fate, they argue in a PLoS ONE paper.

“The fact is that we know very little of the state of our buried archaeological remains from most areas, but we are increasingly becoming aware of their rapid destruction,” the authors said in a press release.

The Ageröd site is near a peat bog that was once a shallow lake in southern Sweden. Those conditions make Ageröd an ideal place for preserving ancient objects made of organic matter, like bone. The artifacts were well-preserved for over 9,000 years. Some signs of degradation were noted during the earlier excavations, but that process has sped up significantly over the last 75 years, the team reports.

They uncovered 61 pieces made of bone, tooth, or antler during their 2019 excavation. Many of those artifacts showed extreme signs of weathering: the artifacts were lighter and the outer layer was gone, smoothening the features of the tools. They compared the newly discovered artifacts to over 3,700 pieces excavated several decades prior, in the 1940s and 1970s. Those that were unearthed earlier were dense with small cracks. By the 1970s, artifacts showed large cracks and signs that the interior of the bone was exposed to the environment – indicating that the artifacts were quickly deteriorating while buried underground. To the researchers, this suggested that artifacts buried in the bog have faced accelerated degradation in the past 75 years.

The team also noticed that they didn’t find any small bones – like those from birds or small animals – even though those pieces were prevalent in the 1940s and 1970s excavations. Bones from birds and small mammals are smaller and lighter, meaning they will degrade much faster than heavier bones. The authors suspect that they didn’t find any small bones during their 2019 excavation because all of them had deteriorated completely by then.

The extreme weathering and possible complete loss of bone artifacts particularly worrisome because “nothing ‘special’ has happened to the Ageröd site,” the authors write in the paper. There haven’t been any major environmental disturbances – for example, a large construction project or draining the bog. Instead, the authors suspect this rapid deterioration is due to climate change and pollution. That means it’s likely that this problem could be affecting other archaeological sites, and that the window to excavate these areas is rapidly closing.

“If we do nothing, wait and hope for the best it is likely that the archaeo-organic remains in many areas will be gone in a decade or two,” the authors said in a press release. “Once it is gone there is no going back and what is lost will be lost forever.”