It may be considered an unusual ingredient in western cuisine, cropping up in a fancy cookbook or local delicacy. But it turns out that seaweed was a common foodstuff among people in Europe for thousands of years. Researchers have found telltale signs of consumption on human teeth at sites from Spain to Lithuania, spanning a period from around 6400BC to the early middle ages. The discovery was a surprise as the rise of farming during the neolithic period was traditionally thought to have resulted in aquatic resources being cast aside. Seaweed was considered a famine food by the 18th century. “The idea of it being a foodstuff really hasn’t emerged in Europe at all, actually,” said Karen Hardy, a co-author of the work and a professor of prehistoric archaeology at the University of Glasgow. The team behind the work say that while evidence of seaweed has been found at archaeological sites before, it was not clear what it was used for, with suggestions including fuel and fertiliser. But the new work offers evidence that seaweed was eaten at many locations across Europe. “These biomarkers came from inside the dental calculus. And so it’s unequivocal. They couldn’t have not chewed it,” said Hardy. Writing in the journal Nature Communications, Hardy and colleagues report how they analysed samples of dental calculus, or tartar, from the remains of 74 individuals from 28 archaeological sites across Europe, from southern Spain to northern Scotland, dating from around 6400BC to the 12th century AD. In total, 37 samples from 33 of these individuals were found to contain biomarkers that allowed the team to explore what they had eaten, with 26 samples containing telltale chemicals indicating the consumption of foods such as seaweed and pondweed. One sample, they add, indicated the consumption of sea kale, a plant noted by Pliny as a sailor’s remedy for scurvy. In some cases, the team could even identify the colour of the seaweed that was eaten: for example, it appears red seaweed was eaten at a middle to late neolithic (3200-2800BC) site in Isbister, Orkney. The team say the evidence suggests that while such foods are rarely eaten in Europe today, they were, until relatively recently, a habitual part of the diet. It is unclear how important seaweed was as a food, but the researchers say it could have been regularly foraged, similar to the way mushrooms and shellfish are still gathered to supplement other food sources today. However, it gradually fell off the menu, becoming a famine food and animal fodder. Hardy said she hoped that the research may change perceptions of seaweed consumption and encourage people to try it, adding that it was not only healthy and tasty but abundant, local and a renewable resource. “It would be a wonderful thing to think that people actually connected in and thought, well, if we ate it before, we can start eating it again,” she said.