For centuries, geological research has been crucial to answering various questions in archaeology. Therefore, archaeologists not only rely on the discipline of geology but also have proven its usefulness in various archaeological investigations. The extreme was reached in 1976 when Colin Renfrew first used the term ‘archaeological geology’ to describe the contribution of geological sciences to geology (Norman and Evan, 1998: 20). In order to emphasize the importance of geology in archaeological work, the Geological Society of America (GSA) established the Department of Archaeology and Geology in 1977. Its purpose is to provide a suitable forum for publishing archaeological geology papers and to promote research and archaeological geology teaching. The early literature on the influence of geology on archaeology is believed to have started in 1830 when Charles Lyell published his ‘Principles of Geology’. In 1863, he published the famous ‘Geological Evidence of Humans in Ancient Times’, in which he used geological antecedents to record the remains and artifacts of early humans. Based on this excuse, this essay attempts to analyze the relationship between archaeology and geology, with the aim of illustrating to what extent the archaeological discipline has benefited from all geological research. For the purpose of this discussion, two main terms will also be studied: archaeology and geology.
According to Pagan (2009), archaeology is the scientific study of the human past and ancient human behavior, from the earliest years to the present. Therefore, archaeology is part of the broader discipline of archaeology, which studies all aspects of ancient and modern humans. But archaeologists are unique among scientists because they study the changes in human culture over a long period of time. On the other hand, Colin and Paul defined archaeology as partly the discovery of past treasures, partly the meticulous work of scientific analysts, and partly the use of creative imagination. Therefore, archaeology is not only a physical activity in the field but also an intellectual pursuit in laboratory research (Renfrew and Bain, 2008: 12). Generally speaking, archaeological research analyzes human culture through the use of cultural relics and other cultural phenomena.
Geology can be defined as the study of the solid earth, the rocks that compose it, and the process of their changes. Geology can also refer to the study of the solid characteristics of any celestial body. It provides insight into the history of the Earth by providing important evidence of plate tectonics, the history of the evolution of life, and past climate. Geology is divided into two categories: planetary geology and applied geology. Planetary geology is related to the exploration of other planets, that is, with the advent of space exploration in the 20th century, geologists began to observe other planetary bodies in the same way that they studied the Earth. This new field of research is called planetary geology (sometimes called astral geology) and is based on known geological principles to study other celestial bodies in the solar system. Applied geology is geology that is used in a variety of practical fields, including mining, engineering, hydrology, and environmental issues, as well as appropriate archaeology.
According to Norman and Evan (1998) in their book ‘Geological Methods for Archaeology’, geology covers the following important roles in archaeological processes. Firstly, geology facilitates the exploration of archaeological sites. The first decision to make in any new archaeological project is where to excavate. In many cases, decisions can be made based on historical records, visible relics of ancient buildings, or the discovery of rich cultural relics. However, to dig deeper into the ground so that a decision can be made on a specific excavation target area and to understand expected artifacts and constructions, geological techniques are increasingly being used. Next, analysis and interpretation of archaeological sites and their surroundings. In archaeological research, the landscape and environment can be reconstructed by geomorphological and Scientological investigations integrated into geology. Therefore, geology is used to analyze the sediments found on the surface, and these sediments provide much evidence of changes in the morphology of the Earth over time. These sediments may be residual materials that are formed on-site by the weathering of the underlying strata, or they may be formed elsewhere and then transported to their current deposition site by wind, water, or humans. The types and quantities of surface materials change with the change of the Earth's surface and climatic conditions, so it provides the best evidence for the evolution of geomorphology. Understanding these changes in a site will help to reconstruct the paleoenvironment at the time of occupation and model the prehistoric land use patterns. By first identifying the ideal livable places at the time, and then conducting geophysical and geological prospecting for these places, the archaeological prospecting of an area was promoted. Information on the excavation process, geology, geomorphology, and sedimentology can help develop excavation strategies. This information can often provide a better understanding of the distribution and nature of buried cultural relics and can explain abnormal surface redistributions of cultural relics, such as scouring slopes or buried sediments. In this process, three main stages are involved: a geomorphological map that describes the geomorphology, drainage patterns, surface sediments, structural features, and any active geomorphic process; an analysis of the erosion process of the carved terrain is recorded, including soil formation, sediment removal or deposition, and structural uplift; and extrapolate today’s landform, climate, and surface sediments to reconstruct the paleoenvironment and paleoclimate when the site was occupied. Geology helps to analyze archaeological artifacts because it can be used to determine the source of raw materials used in artifacts. For example, since 5500 BC, the development and dissemination of iron technology have been obvious in the production of clay pots in different locations in the Tigris-Euphrates valley. These designs are commonly used and originated from unique locations, so from an archeological perspective these jars seem to be exported from these locations. However, since the materials used in each location are determined to be local materials, the export is technology, not ceramics. Each site should have its own production center, making full use of raw materials: it should also have representatives from the 'parent company' to ensure quality and artistic control (Norman and Evan, 1998: 20).
Both archaeology and geology use various dating techniques to obtain the absolute and relative dates of various materials. The methods used in dating can be explained by various laws or principles. The principle of uniformity is the basic principle of geology proposed by the Scottish physician and geologist James Hutton in the 18th century. This principle states that the currently observed geological processes in operation to change the crust operate in roughly the same way during the geological period. In Hutton's words, the present is the key to the past, and the past history of our planet must be explained by what can now be seen. The intrusive relationship principle implies a transversal invasion. In geology, when an igneous rock intrusion passes through a sedimentary rock formation, it can be determined that the igneous rock intrusion is younger than the sedimentary rock. There are several different types of invasions, including strains, rocks, foundation stones, thresholds, and dams. This principle can be applied to archaeology to determine the age of sediments. The principle of horizontal relations refers to the formation of the fault and the age of the sequence through which the fault passes. Faults are younger than the rocks they cut, therefore, if a fault is found to penetrate some layers other than those above it, the cut layer is older than the fault, and the uncut layer must be younger than the fault. Finding the critical layer in these situations can help determine if the failure is a normal failure or a thrust failure. In archeology, this principle can determine the age of cultural relics found in such fault rocks. The law of superposition states that sedimentary rock in a sequence that is not altered by the structure is younger than the layer below it and older than the layer above. Logically, the newer layer cannot slide under the previously deposited layer. This principle allows the deposition layer to be considered as a form of a vertical timeline, that is, a partial or complete record of the time elapsed from the deposition of the lowest layer to the deposition of the highest layer. Stratigraphy can also be used to determine the relative age of various sites. This is done by analyzing the location of the stratum, the style, and the absorption of transient elements. Objects that are in the same undisturbed formation are considered to be the same age, objects that are in shallower formations are considered younger, and those that are found are considered older.
Both archeology and geology can be used to understand past events. For example, through the study of geology, geologists can list some prominent events that should affect sediments and or rocks, causing them to change from one form to another. On the other hand, archeology is also used to understand past events, which is done by analyzing cultural relics, ecological facts, structures, and characteristics.
However, these two studies, archeology and geology, are different in different ways. Geology deals with the analysis of the Earth and other planets in its branch of planetary geology. However, until now, archeology has focused on analyzing materials found on the Earth, especially as archeology is concerned with understanding human cultures that were thought to have been found only on the Earth in the past. Geology primarily studies the Earth, solid materials, and rocks. They are committed to understanding the history of the Earth. On the other hand, archaeology studies humans by using artifacts and remains that ancient humans can find on the ground. Archaeology involves the analysis of organic and inorganic materials, that is, it involves modified and unmodified remains, including animal and plant remains. On the other hand, geology involves inorganic materials including rocks, and never includes animals and plants.
Finally, it can be said that archaeology and geology are closely related disciplines. Therefore, not only is the archaeological process impossible without geology, but the entire process of archaeological excavation requires geological knowledge. It is based on this understanding that Colin Renfrew established the term ‘archaeological geology’ in 1976 to unite these two disciplines, as they seem to be inseparable from each other.