Paper No. : 03 Archaeological Anthropology Module : 06 Relative dating methods Development Team Principal Investigator Prof. Anup Kumar Kapoor Department of Anthropology, University of Delhi Paper Coordinator Dr. M. K. Singh Department of Anthropology, University of Delhi Dr. K. Polley Content Writer Department of Anthropology, Haldia Government College Content Reviewer Prof. Falguni Chakraborty Department of Anthropology, Midnapur University 1 Archaeological Anthropology Anthropology Relative dating methods Description of Module Subject Name Anthropology Paper Name 03 Archaeological Anthropology Module Name/Title Relative dating methods Module Id 06 2 Archaeological Anthropology Anthropology Relative dating methods 1. INTRODUCTION Dating is an indispensable tool in the field of evolutionary investigations. It helps researchers to make a better assessment of time of any relict objects like fossils, artifacts and also geological deposits. There are two different approaches to dating, namely- Absolute or Chronometric Dating and Relative Dating. Dating Methods Absolute Dating Relative Dating Relative Dating gives information about the age of an object in relation to other objects. In another way, it can be said that this dating method can determine whether any object is older or younger than other objects. With the help of this method of dating archaeologists can group or rank various archaeological materials like artifacts, fossils etc. according to their relative age. Thus, the relative method of dating produces only comparisons of age or date, not actual or calendrical date of an object. Stratigraphic analysis is an essential component of this method of dating. Besides Fluorine test method help to determine the relative age of different objects belonging to the same stratum. In possible cases, the technique of Palynology and Pedology is also applied to achieve a more or less correct date for an object. The approach of relative dating has its root in the science of Geology, particularly in Stratigraphy. British geologist William Smith (1800) formulated the two basic principles of stratigraphy. The first of which is known as the Law of Superposition, it means if one series of rock lies above another then the upper series was formed after the lower series. The second principle is related to the Biostratigraphy; this principle indicates that each bed or each group of beds contains a characteristic assemblage of fossils (Walker, 2005:165). On the basis of the aforesaid laws various Stratigraphic units can be placed in relative order of age. In the field of archaeology use of the said laws of stratigraphy have been used since the time of Antiquerians (Green, 2003:18-23). However, after 1950’s use of more advanced 3 Archaeological Anthropology Anthropology Relative dating methods techniques of stratigraphy came in the appearance (Green, 2003:108-113) and have been increasingly applied in the field of archaeology. 2. RELATIVE DATING METHODS: A SHORT SURVEY Within the class of relative dating methods, there are mainly four different methods of dating, namely, Typological dating of ancient artifacts, Stratigraphic dating, Fluorine analysis method of dating and Pollen analysis method of dating. Most of the said relative dating methods require limited technological sophistication as well as funding also. Beside the afore said methods other relative dating methods like Obsidian hydration method, Amino Acid Racemization Method etc. are recently developed and being applied in the field of archaeological research. Brief descriptions of all these methods of dating are given below. 2.1. Typological Method of Dating: Classification is one of the most fundamental interpretative activities in the field of natural sciences. In archaeology classification of various cultural materials is known as typology. Typological classification of material remains of ancient culture has a long history in archaeology; it probably dates back to the beginning of archaeology itself. Besides making classification or subdivision of various data during archaeological excavation and exploration, typological classification often helps archaeologists to determine the relative age of various artifacts. In the nineteenth century, observations about the types of artifacts, collected from different layers led to the creation of a time frame for prehistory, often known as the ‘Three Age System’. It was based on the introduction of tools made from stone, the bronze and then iron. Despite the presence of many flaws in this scheme, the terms are still used today to distinguish different periods of the past (Grant et al, 2008:98). In the typological method of dating at first various attributes of an artifact like shape, design, raw material or fabric etc. are selected to characterize or classify that artifact into a particular ‘form’ or artifact ‘type’, after that the typified or classified artifact is compared to the other type of artifacts to allocate the newly typified artifact in a particular time period. In this way once a good typological sequence for an area is established it can be referred to when new finds and sites are discovered and used to cross date them (Andrefsky, 2005:66; Grant et al, 2008:98). As an example to this scheme it can be said that if someone finds a piece of pottery and takes it to a museum, typology will help him to classify the potsherd to a particular time period. 4 Archaeological Anthropology Anthropology Relative dating methods Fig 1: Example of typological sequence: Development of copper and bronze axes. (After Grant et al, 2008). The typological scheme of classification of human culture and various archaeological materials has its root in the time of ‘Antiquarianism’, or at the time of ‘Enlightenment’ period. It was that time, when the dominant concern of the archaeologists was to bring order and system to the mass of relict objects, collected by excavations or explorations. This scheme of classification was mainly influenced by the ‘System of Nature’ of Linnaeus. In later time influence of Linnaeus and other naturalists provided a methodological foundation for the later development of artifact classification (Ellis, 2008, cited in Pearsal, 2008:1019). Now a day’s typological classification of artifacts has been developed a lot and newer techniques like seriation technique, study of the curation of artifacts etc. are used by modern archaeologists to classify an artifact of a more accurate sense. 2.2. Stratigraphic Dating Method: Stratigraphy is a sub-discipline of Geology. It is the study of the origin, physical characteristics and spatial relationships of stratified rocks, primarily to understand the history of events documented in the strata (Delson et al, 2004). Usually sedimentary rocks are studied in stratigraphy, however layered igneous rocks and even layered metamorphosed rocks can also be studied using principles of stratigraphy. The science of stratigraphy is mainly governed by three basic principles or laws; they are Principle of Superposition, Principle of original Horizontality and Principle of Lateral Continuity. The principle of superposition says that means if one series of rock lies above another then the upper series was formed after the lower series (Walker, 2005). The principle of original horizontality says that strata are horizontal or nearly so when they are deposited; according to the principle of lateral continuity it can be said that all parts of a stratum, disrupted by lateral activity, were once joined in a single connected layer (Delson et al, 2004:1384). 5 Archaeological Anthropology Anthropology Relative dating methods Basic Principle Branches Principle of Superposition Lithostratigraphy Biostratigraphy Principle of Original Chronostratigraphy Horizontality Magnetostratigraphy Isotope-stratigraphy Principle of Lateral Continuity S t r a t i g r a p h y gp a h i r ar St t Cyclostratigraphy Table 1: Basic Principle and branches of Stratigraphy. Stratigraphy is used to date rocks and fossils of an area on the basis of the principle of superposition. This principle helps geologists and archaeologists to put various historical events in order. Succession of events in one area can be correlated with other on the basis of original horizontality and principle of lateral continuity. Sometimes it can be done by comparing fossils of two areas or by the use of the knowledge of biostratigraphy. In Stratigraphy rock strata are classified according to their nature and age of origin, lithological components and biological components. On the basis of the said features, three different branches of stratigraphy- lithostratigraphy, biostratigraphy and chronostratigraphy have been developed. Lithostratigraphic studies are based only on the nature of rocks and minerals of stratigraphic units alone. Various lithostratigraphic units can be classified as laminae, bed, formation, groups etc. on the basis of their lateral extent and relative thickness in a particular area. Biostratigraphy classifies various Stratigraphic units on the basis of the fossils found in each of them. Biostratigrapher tries to correlate various Stratigraphic units on the basis of evolutionary relationship or absolute age of the fossil remains found in various strata. Chronostratigraphy tries to correlate various Stratigraphic units on the basis of their relative age. The major objective of chronostratigraphy is to gather all strata of the same age into the same chronostratigraphic unit (Delson et al., 2004). 6 Archaeological Anthropology Anthropology Relative