When these plots were all put next to one another, along with temperature data from tree rings, D'Anjou saw a story emerge. For the first 4,000 or so years of the record, human fecal sterol levels were nearly zero, and the levels of the hydrocarbons were low too. The plant waxes suggest that the land was forested. Then, about 2,250 years ago, the sterol and hydrocarbon levels spike dramatically, and a greater proportion of the land was cleared. The levels of fecal sterols remain elevated for hundreds of years, often falling after a sudden temperature drop, which might have made agriculture untenable in the already-chilly Arctic. Sterol levels rise again when the temperature warms, but a significant dip occurs around 550 AD, continuing gradually downward, in tandem with records of migrations in Scandinavia, mostly for political and socioeconomic reasons. Levels later recover, but another dip occurs around the time of the Black Plague in the 14th century, when historical records show that more than 80% of the area's farms were abandoned.
