Science

In short, archaeology is dependent on geology. The longer answer is that geological principles and methods are at the very core of archaeological site interpretation methodologies. They are the foundation really. The understanding we get from archaeology can only happen if we know when something happened, and if the things we find are associated with that thing. From that point, we can start to say things confidently. If we don't have those two basic pieces of information, we cannot say anything and it is just stuff in the ground. To date, the only way to get those two points of information is through geology. Geology provides archaeology with the concept of stratification to determine this. Stratification is the form of strata in a given area, and how they relate to one another. Strata refers to horizontal layers of sediment soil, that were derived from the erosion of surrounding rocks. Stratification is the principle that younger layers of soil sediment will typically be on top of, or superior to older sediment layers. Which means the deeper the soil layer below surface, the older the soil layer. An important digression is that since there are different conditions over time when the rocks erode, the soil strata are different colors and compositions, so the different strata can be differentiated. Back to the core points. A principle of archaeology is that sites form while they are part of daily life, so you assume that the strata that holds the archaeology was the ground surface at the time it was in use. This is unless you have obvious signs of something having been buried, which can also be understood through stratification but again, that's a whole other discussion. This is where geology gets applied, when we find archaeology, we measure how deep it is in the ground and where it is horizontally also, this information is called provenance and is basically, your proof as an archaeologist that this thing was used by these people at this time. Otherwise, it is speculation.