Focus of the research is the Lofoten Islands in northern Norway : Wiki Commons
For researchers who study Earth’s past environment, disentangling the effects of climate change from those related to human activities is a major challenge, but now University of Massachusetts Amherst geoscientists have used a biomarker from human feces in a completely new way to establish the first human presence, the arrival of grazing animals and human population dynamics in a landscape.
“We are really excited about how well this method worked,” D’Anjou says. “Without even knowing it, early settlers were recording their history for us, and in the most unlikely of ways, in their poop. The prehistoric settlers and their livestock pooped and their feces washed into the lake, which over time left a record of trace amounts of specific molecules that are only produced in the intestines of higher mammals. When you find these molecules at certain concentrations and in specific ratios, it provides an unmistakable indicator that people were living in the area.”
In addition, the geoscientists used two other molecular markers to reconstruct the vegetation history: relative length of carbon molecules found in leaf waxes (different in forest and grassland), and pyrolytic polycyclic aromatic hydrocarbons (PAH) as evidence of fire in the Lake Liland area. They say that taken together, the sediment cores, vegetation changes and fire records clearly define a pre-settlement period with no detectable human activity in the lake’s water catchment area from about 7,300 to 2,250 years ago.
At that point, however, changes in the background state appear in the record, marking an “abrupt shift” to significantly increased levels of pyrolytic PAH first, followed by increased human fecal material. This likely indicates that as people moved in, they first cleared the land by burning before establishing a permanent settlement, the researchers say. “This interpretation is bolstered,” they add, by the leaf wax record that shows a “marked transition to a more grassland-dominated landscape beginning at this time.”
After the initial influx of people to the region, D’Anjou and colleagues say the record shows a lull in human activity from about 2,040 to 1,900 years ago, reflected in all markers. After this, the human and livestock populations steadily increased to a local maximum around the year 500, based on the fecal record, then fell again to a second minimum around the year 850.
The climate scientists note a further decline in human activity and population to another minimum at about AD 1750 that coincided with the highest relative grassland cover for the entire 7,300-year history. Findings related to human activity over the past 7,300 years in northern Norway correlate well with other climate reconstructions, in particular summer temperature patterns indicating poor vs. fruitful growing seasons. This shows that the early settlers were vulnerable to small changes in summer temperature at this far northern location.
Overall, the authors say, the new fecal markers are likely to prove valuable in many other places, to distinguish natural from human factors that influenced the environment in the past.
This work was funded by the U.S. National Oceanographic and Atmospheric Administration.