Trained archaeologist and Corinium Museum's Schools and Families Officer Rebecca Shellenberger on how context is king when it comes to determining the age of archaeological artefacts
One question that students ask me frequently is, “Yes, but how do you know that pot sherd is from that age?” Excellent question. So, how do we know?
Well, let’s begin with a principle of geology – the law of superposition. This law states that layers of earth/soil increase in age as it gets deeper…the oldest layer is at the bottom as long as it is not disturbed. This law applies to human habitation as well – the layer that we walk upon is younger than deeper layers. This means that as archaeologists dig deeper in the earth, the older the civilisation. This is true as long as the layers of soil are undisturbed. Disturbances can occur in many ways – they can come from natural occurrences such as an earthquake or the uprooting of a tree with deep roots from a storm, or they can be helped along by borrowing animals such as a mole. Animals can disturb the layers and kick soil up to the surface from deep below, and sometimes they may even kick up an ancient artefact. Keep your eyes peeled! If you find something amazing, don’t forget to report it to somewhere such as your local museum or the Portable Antiquities Scheme.
As you look at the landscape, you may see variations in how layers are deposited – maybe there has been an earthquake that shoves part of the layers skyward (mountains!) which means that some layers may be vertically higher than they originally were. Geologists can match different soil profiles back together like a puzzle that can create a lithic (stone), history, or a lithistory (hehe just kidding, that’s not a word) of landscapes. They can even do this across oceans!
We can do a similar thing in archaeology. We can analyse and match different soil profiles that contain specific artefacts. We operate on the law of superposition that assumes that the layer on top is younger than the layer beneath. From the artefacts we find, we can also create typologies – ways to categorise artefacts from a specific age. Today, archaeologists gather things such as specific types of pottery or brooches from thousands of years ago; but 2000 years in the future, archaeologists may find bits of furniture from the late 1990s with the mysterious moniker of “IKEA” written on it. It was/is a popular brand of furniture that many households have, and the sheer number of artefacts from this place will give future archaeologists clues about how we lived around the turn of the century. Sometimes we are really lucky and we find ways to corroborate the supposed date – like something with a date written on it. We can also use scientific tools such as carbon dating to help obtain dates. This works best when the layer and context is sealed undisturbed so that the dates are as accurate as possible.
We are interested in the culture, or the way people lived, from the past. Archaeologists study the material culture of a society in the form of artefacts, but almost as important as the artefact itself is the environment, or context in which it’s found. How does that artefact relate to other artefacts near it, and in within the space where it was discovered? If the context is disturbed through environmental, animal or human practices, we may lose as much or even more of the information as the artefact can give us alone. his is one of the reasons that archaeologists ask the public to not dig below the plough line – about 30 cm or so. The surface where we walk, live and farm is naturally disturbed. Artefacts that may be brought to the surface through natural processes such as earthquakes or animal burrows are a delight to find; but when people without archaeological training dig deeply looking for that piece of metal, for example, they may be destroying precious information. We need people’s keen eyes and metal detectors to help identify new archaeological sites or discoveries, but always keep in mind the importance of superposition and context.
