Discovery of preserved 3,775-year-old logs supports ‘wooden vault’ as climate solution

A new study published in the journal Science suggests that a plain old newspaper could help refine strategies to combat climate change.

A team of researchers led by Ning Zeng, a professor of atmospheric and oceanic sciences at the University of Maryland, analyzed a 3,775-year-old log and the soil from which it was quarried. Their analysis, published on September 27, 2024, found that the log had lost less than 5% carbon dioxide compared to its original state thanks to the low permeability clay soil that covered it.

“The wood is beautiful and strong. You could probably make a piece of furniture out of it,” Zeng noted.

Understanding the unique environmental factors that helped keep this ancient log in pristine condition could help researchers perfect an emerging climate solution known as “timber vaulting,” which involves harvesting wood that is not commercially viable , such as trees destroyed by disease or wildfires, old furniture or unused building materials and burying them to stop their decomposition.

Trees naturally sequester carbon dioxide – a potent gas that warms the planet – for as long as they live, making tree planting projects a popular method of mitigating climate change. But on the other hand, when trees die and decompose, these greenhouse gases are released into the atmosphere, contributing to global warming.

“People tend to think, ‘Who doesn’t know how to dig a hole and bury wood?’ “, Zeng said. “But think about how many wooden coffins have been buried in human history. How many of them have survived? For a time scale of hundreds or thousands of years, we need good conditions .”

In 2013, while conducting a wooden vault pilot project in Quebec, Canada, Zeng discovered the 3,775-year-old log that became the focus of the study – a chance encounter that, for Zeng, was “a bit miraculous”. While digging a trench to bury fresh wood, Zeng and other researchers spotted the log about 2 meters below the surface.

“When the excavator dug a log out of the ground and threw it at us, the three ecologists I had invited from McGill University immediately identified it as western red cedar,” Zeng recalls. “You could tell how well preserved it was. I remember standing there thinking, ‘Wow, here’s the evidence we need.'”

Although previous studies have analyzed ancient samples of preserved wood, they tend to neglect surrounding soil conditions, according to Zeng.

“There is plenty of geological and archaeological evidence of wood preserved from hundreds, even millions of years ago, but the goal of those studies was not ‘How can we design a wooden vault to preserve this wood?’” Zeng said. “And the problem with designing a new experiment is that we can’t wait 100 years to get the results.”

Shortly after the Quebec excavations, UMD collaborators at MAPAQ, a Montreal government department, carried out carbon dating to determine the age of the log. Then, in 2021, Distinguished University Professor Liangbing Hu from UMD’s Department of Materials Science and Engineering helped Zeng analyze the microscopic structure, chemical composition, mechanical strength and density of the 20-year-old sample. 3,775 years old. They then compared these results to those of a freshly cut Eastern red cedar log, which revealed that the oldest sample had lost very little carbon dioxide.

The type of soil covering the log was the main reason for its remarkable preservation. The clay soil in this part of Quebec had particularly low permeability, meaning it prevented or significantly slowed down oxygen from reaching the log while preventing the entry of fungi and insects, the decomposers that we usually found in the soil.

Since clay soils are common, wooden arches could become a viable and inexpensive option in many parts of the world. As a climate solution, Zeng noted that wood vaults are best paired with other tactics aimed at slowing global warming, including reducing greenhouse gas emissions.

As he and his colleagues continue to optimize the wooden vaults, he looks forward to putting what they’ve learned into practice to help curb climate change.

“It’s a pretty exciting finding,” Zeng said of this latest study. “The urgency of climate change became such an important issue that there was even more motivation to launch this analysis.”