A study by the University of Wisconsin-Madison has revealed that buried fossils in 15,000 year-old soil could contain high carbon content. Moreover, when disturbed through "erosion, agriculture, deforestation, mining and other human activities," they will become large contributors to further exacerbate global warming and climate change.

The work suggests that fossil organic carbon in buried soils is widespread and, as humans increasingly disturb landscapes through a variety of activities, a potential contributor to climate change as carbon that had been locked away for thousands of years in arid and semi-arid environments is reintroduced to the environment.

Ancient fossil soils could be found at just about anywhere in the part of the world, at practically every country under its river, volcano and other sediments. While most will probably remain buried, some will be exposed over time.

Erika Marin-Spiotta, a University of Wisconsin-Madison assistant professor of geography and the lead author of the new study, is worried once these fossil soils get disturbed.

"Only recently have scientists become more concerned about deep soil carbon as we are finding it is more reactive than we ever imagined," Marin-Spiotta said. "There is probably a lot more out there than we know."

She said carbon in soil can be released as carbon dioxide into the atmosphere through microbial decomposition and closer to the earth's surface. She noted most research involved only checking the top 30cms of soil.

Marin-Spiotta and her colleagues studied "Brady soil," formed some 15,000-13,500 years ago. Brady soil can be found in modern-day Nebraska, Kansas and other parts of the Great Plains. An accumulation of "wind-borne dust" eventually buried deeper underground.

"Most of the carbon (in the Brady soil) was fire derived or black carbon," Marin-Spiotta said. "It looks like there was an incredible amount of fire."

The region where the Brady soil formed was not glaciated, but underwent radical change as the Northern Hemisphere's retreating glaciers sparked an abrupt shift in climate, including changes in vegetation and a regime of wildfire that contributed to carbon sequestration as the soil was rapidly buried by accumulating loess.

"The world was getting warmer during the time the Brady soil formed," Joseph Mason, UW-Madison geography professor and study co-author, said. "Warm-season prairie grasses were increasing and their expansion on the landscape was almost certainly related to rising temperatures."