Porous Contexts Trace Ecology and the Problem of Molecular Belonging in Archaeology

For decades, archaeologists have treated ancient objects like sealed boxes. When a pot sherd is found in a specific layer of dirt, the assumption is that everything stuck to it or inside it belongs to that exact moment in time and that specific place. This logic has served the field well, organizing history into neat categories of who made what, where, and when. However, a new wave of scientific tools has begun to look inside these boxes with such extreme sensitivity that the neatness starts to dissolve. These tools can detect microscopic traces of DNA, fats, and proteins that are far smaller than the human eye can see. The problem is that these tiny molecular traces do not always stay put. They can move through water, stick to different surfaces, or survive for centuries in ways that do not match the visible history of the object they are found on. This creates a puzzle: just because a molecule is found on an ancient pot does not mean it was put there by the person who used that pot, or that it belongs to the time the pot was buried.

Lars Morten Fuglevik, a researcher at the Norwegian Institute for Cultural Heritage Research, addresses this growing confusion in a new study. He argues that archaeologists can no longer assume that a molecular signal automatically belongs to the object or the dirt layer from which it was taken. Instead, he proposes a new way of thinking called "trace ecology." This approach treats the environment around an object not as a static container, but as a dynamic medium where traces move, change, and mix over time. To test this idea, Fuglevik looked back at five ancient cooking pots from medieval Oslo, Norway. These pots had been analyzed years earlier to find out what people ate, but the original study did not account for how the molecules might have moved after the pots broke. By re-examining these old samples with his new framework, Fuglevik shows that while we can detect what molecules are present, we often cannot be sure exactly when they arrived or what specific event they represent.

The core of the problem lies in the difference between finding a signal and knowing what it means. Imagine holding a piece of a broken cooking pot that has a black crust on the inside. To the naked eye, this crust looks like a single layer of burnt food from one meal. But under a microscope, that crust is a history book written in layers. It might contain fats from a fish dinner cooked ten years ago, smoke from a fire used to dry the pot, and soil particles that stuck to it after it was thrown away. When modern scientists use advanced machines to read the chemical makeup of this crust, they can identify specific types of fats or proteins. However, the machine cannot tell if those fats came from the last meal cooked in the pot, or if they seeped in from the soil while the pot sat in the ground for centuries. Fuglevik calls this situation a "porous context." It means the boundaries we draw around an object in the field are not tight enough to hold the molecular evidence that scientists are now trying to extract.

To understand how this works, Fuglevik breaks down the life of a trace into four different stages. First, there is the recorded context, which is the official label archaeologists give a find, such as "found in the kitchen floor of 1200 AD." Second, there is the material microcontext, which is the tiny, immediate spot where the molecule actually sits, like a single pore in the clay or a speck of soot. Third is the comparative-analytical context, which involves the lab equipment and reference data used to identify the molecule. Finally, there is the curatorial context, which covers everything that happened to the object after it was dug up, including how it was washed, stored, or handled in a museum. Fuglevik argues that a molecule might be authentic and ancient, but it could have moved from the second stage to the first, or been altered by the fourth. If researchers treat the recorded context as the only truth, they risk building a story on a foundation that has shifted.

To illustrate this, Fuglevik revisited five specific cooking pots from medieval Oslo that had been analyzed in a previous study. These pots came from different locations, including a leveling deposit (where dirt was moved to make ground flat), a refuse pile, and a cultivated field. The original analysis had identified traces of fish, animal fats, and what looked like fermented apple products, such as cider or wine, on the pots. The researchers had assumed these flavors belonged to the meals cooked in those specific pots at the time they were used. Fuglevik's re-evaluation suggests a more cautious reading. He points out that the pots were found in layers of dirt that had been moved around. The "cider" or "wine" signal, for instance, might not have come from a drink poured into the pot. It could have come from smoke, from the soil, or from a chemical reaction that happened long after the pot was broken. The original study did not have the right controls to tell the difference, such as comparing the inside of the pot to the outside, or testing the dirt right next to it.

The result of this re-reading is not that the previous findings were wrong, but that the story they told was too specific. Fuglevik suggests that while we can be sure the pots once held animal fats or plant materials, we cannot be sure they held a specific dish like fish stew or a specific drink like cider. The molecules are real, but their connection to a single meal or a single household practice is uncertain. This does not mean archaeology is failing; it means the field is maturing. The new sensitivity of the tools is revealing a complexity that older methods simply could not see. The challenge now is to stop assuming that a molecule found on an object tells the whole story of that object's life. Instead, researchers must prove that the molecule belongs to the specific event they are studying.

Fuglevik proposes a new way to report these findings, which he calls a "trace ecology statement." This is a checklist that researchers must include in their papers to explain exactly how they connected a molecule to a historical event. It forces them to ask: Did we check the soil next to the pot? Did we check the outside of the pot? Did we account for how the pot was washed in the museum? By answering these questions, scientists can separate what they know for sure from what they are guessing. For example, if a signal is found only on the inside of a pot and not on the outside or in the surrounding dirt, it is much more likely to be from cooking. If the signal is everywhere, it might just be from the environment. This approach turns the "porous context" from a problem into a tool for better science.

The implications of this work extend beyond just cooking pots. It changes how archaeologists handle all ancient materials, from bones to soil samples. It suggests that museums should stop cleaning objects as thoroughly as they used to, because washing might remove the very traces that future scientists need to study. It also means that when digging, archaeologists should save samples of the dirt right next to an object, not just the object itself. These paired samples act as a control, helping to prove whether a molecule came from the object or the ground. Fuglevik emphasizes that this is not about being afraid of new technology, but about using it responsibly. The goal is to keep the link between the evidence and the story strong, even as the evidence becomes more detailed.

In the end, the study of medieval Oslo pots serves as a warning and a guide. It shows that the more precisely we can identify a molecule, the more carefully we must check where it came from. The five pots from Oslo did not provide a clear menu of medieval meals, but they did reveal a crucial truth about how history is preserved. The past is not a series of sealed boxes waiting to be opened. It is a complex web of moving parts, where traces travel, mix, and survive in unexpected ways. By acknowledging this porosity, archaeologists can build stories that are not just exciting, but also honest about what the evidence can and cannot tell us. The object remains the center of the story, but it is no longer the only place where the truth is found.