November 27, 2012
Biomarkers In Poop Help Track Activity Of Prehistoric Humans
April Flowers for redOrbit.com - Your Universe Online
Disentangling the effects of climate change from those related to human activities is a major challenge for scientists who study the Earth's environmental history. Researchers from the University of Massachusetts, Amherst have recently gotten creative with poop, using a special biomarker found in human feces to establish the first human presence, the appearance of grazing animals and human population dynamics in a landscape.
"We are really excited about how well this method worked," doctoral student Robert 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."
The results of their study were published online in Proceedings of the National Academy of Sciences.
Raymond Bradley, director of the Climate System Research Center at UMass Amherst adds: "This approach opens the door to other studies, where the presence of humans is uncertain; we believe it has great potential for much wider applications in archaeology."
D'Anjou conducted his research just north of the Arctic Circle at Lake Liland, which is located in the Lofoten Islands in northern Norway. Humans were thought to have lived in prehistoric settlements at this location from the early Iron Age through the Viking period. D'Anjou and his colleagues extracted two sediment cores from the lake bottom and established their chronology using radiocarbon measurements and the presences of volcanic ash from Iceland. The core samples provided a continuous record extending back from present day to roughly 7,000 years ago.
Lakebed sediments have been used by paleoclimatologists for quite a while. Markers such as charcoal from human fires and pollen from cultivated plants serve as a natural archive of environmental changes that can be used to approximate the time of the first human impact on the environment. The indirect indicators, however, must be used with care when reconstructing the history of a location because it is not always clear that they indicate human activity in the area.
In contrast, the presence of a molecular biomarker directly linked to humans — one which has been transmitted through their bowel movements — is much less ambiguous. It offers "a strong human signal" that can be dated with "excellent chronological control."
The team extracted the compound called coprostanol — a molecular marker formed from the digestion of cholesterol in the human intestinal tract — from the sediment cores. They also extracted other sterols characteristic of other mammals to determine the presence of sheep and cattle. The two types of biomarkers allowed them to produce a long-term record of the presence and relative population size of humans that extends back over several thousand years at the site.
The team of geoscientists used two additional molecular markers to reconstruct the vegetation history at the site: the relative length of carbon molecules found in leaf waxes (which are different in forests compared to grasslands) and so-called pyrolytic polycyclic aromatic hydrocarbons (PAH) as evidence of fire in the Lake Liland area.
The study asserts that the sediment cores, vegetation changes and fire records, when taken together, 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.
However, an "abrupt shift" marked by changes in the background state appears in the record at that point. Significantly increased levels of pyrolytic PAH first followed by increased human fecal material likely indicate that as people moved in, they first cleared the land by burning before establishing a permanent settlement. The authors added that this interpretation is further supported by the leaf wax record, which shows a "marked transition to a more grassland-dominated landscape beginning at this time.”
The study, funded by the U.S. National Oceanographic and Atmospheric Administration (NOAA), points out that after the initial influx of people to the region, the sediment record shows a lull in human activity from about 2,040 to 1,900 years ago, which is reflected in all of the markers. After this point, human and livestock populations increased steadily, reaching a local maximum around the year 500 AD, based on the fecal record. This fell again to a second low around the year 850 AD.
About 1750 AD, the scientists note a further decline in human activity and population that coincided with the highest relative grassland cover for the entire 7,300 year history. Other climate reconstructions — in particular summer temperature patterns indicating poor vs. fruitful growing seasons — also correlate well with this study's findings related to human activity over the past 7,300 years in northern Norway, indicated that early settlers were vulnerable to small changes in summer temperatures at this cold northern locale.
The new fecal markers are likely to prove valuable for a variety of other studies, helping to distinguish human from natural factors that influenced the environment in the past.