Archaeology is inherently destructive. Once we dig up a site that part is gone forever; we may have gathered artifacts, but we have also removed them from their context, which can be more important to our interpretation than the artifact itself. This is why we go through so much paperwork. We try to recreate the context on charts so tomorrow, or even a decade from now, when another archaeologist finds a interesting ceramic in a collection which I pulled from the ground, they can look up my unit and see how the soil looked and the artifact distribution from where it was found, as well as the unit as a whole. We chart in every artifact we find and how deep it is in centimetres, and the layers of soil we move through, as well as any features we find. Features are immovable artifacts, like a plank of wood, or a collection of artifacts which would lose part of its meaning by moving it, such as a hearth. We chart and record everything of value so the context is not lost and some of what we destroy is preserved in another fashion. For example, if an old building was to be torn down for parts then taking pictures would preserve it in another form. The intact building is the context, the parts are the artifacts, and the pictures are our paperwork. The building needs to comedown to get at the valuable parts within but the pictures preserve the building for future generations.
The context we capture in our paperwork shows us the layout of the site overall. To use a real example from my first unit on the site, it has a modern plough zone of 10 centimetres or so, filled with artifacts of varying sorts. I found two pieces of bone (probably pig), three pieces of glass, 4 pieces of differently decorated pottery, and a nail. Then the next layer is 7 centimetres or so of a sandy soil interspersed with rodent holes, where a piece of cobalt blue pottery and half a rats jaw was found. We then come to a rich black organic soil which has never been farmed which goes all the way down to about thirty centimetres where I ended the unit and I started to hit clay. All of this information has been diligently put into standardised forms. So if another archaeologist wanted to analyze my unit they would look at my artifact distribution and soil stratigraphy and could come to some conclusions without ever being at the site themselves. They would understand that all the artifacts in the plough zone could have been hundreds of feet from where they were originally laid down from countless seasons of having the soil tossed around by ploughing; and as such disregard their modern context. In the next layer rodents could have moved artifacts from their original position through digging and this layer may have also been a plough zone, although much older and as such the artifacts would have been closer to their original position. Finally once we find the next layer which is sterile of artifacts and hit clay we know that no other artifacts will be found in this unit and can move to another unit to start the search anew.