Comprehensive Study Notes on Relative Dating Methods in Archaeology
Overview of Archaeological Dating Methods
In the field of archaeology, materials recovered from excavations and explorations are dated using two primary methodologies: Absolute Dating and Relative Dating.
Absolute Dating: This method provides precise dates for artifacts using scientific techniques. Occasionally, absolute dates are derived from internal historical evidence found in documents, inscriptions, copper plates, seals, coins, inscribed portrait sculptures, and monuments.
Relative Dating: This method establishes a tentative chronological sequence. It relies on context-based analysis, including archaeological stratigraphy, seriation, palaeography, linguistic styles, and art or architectural features.
Historical Evolution: In the 18th and 19th centuries, age estimation was largely speculative guesswork. As research progressed, the accumulation of data and improved analysis allowed for more narrowed approximations. Relative dating remains vital when absolute scientific dates are unavailable or unfeasible.
Stratigraphy
Definition: The study of cultural and archaeological layers found in successive, undisturbed deposits. Artifacts can be dated relatively based on which layer they occupy.
Origin: The concept was borrowed from geology. Sir Charles Lyell established the foundations of stratigraphy in his 1830 book, Principles of Geology.
Geological Laws Applied to Stratigraphy:
Laws of Superposition: The oldest layer is at the bottom, and layers get younger as they go up.
Laws of Original Horizontality: Layers are originally deposited horizontally.
Laws of Original Continuity: Layers are assumed to have originally extended in all directions unless obstructed.
Laws of Faunal Succession: Fossil organisms succeed one another in a definite and determinable order.
Key Archaeologists: The concept was integrated into archaeology by C. J. Thomsen, J. J. Worsaae, Kathleen M. Kenyon, and Mortimer Wheeler.
The Harris Matrix: Developed by Edward C. Harris in the 1970s and detailed in his 1979 book, Principles of Archaeological Stratigraphy.
Harris argued that geological laws could not be applied directly to archaeology without adaptation.
The basic principle is that if cultural layer A lies on layer B, layer B must have been deposited before layer A.
Succession of layers provides a chronology from earliest to latest. For example, a sequence containing Palaeolithic, Microlithic, and Neolithic tools in distinct layers determines a chronological cultural progression.
Seriation and Typology
Seriation: A relative dating method based on the style, type, and technique of artifacts. It is divided into two categories:
Stylistic Seriation: Ordering artifacts by similarities in style and attributes.
Examples from Harappan sites: Dish-on-stand, S-shaped jars, and perforated jars.
Example from Jorwe ware: Carinated vessels are diagnostic of this cultural phase.
Frequency Seriation: Ordering artifacts based on their origin, peak popularity, and eventual disuse. The quantity and frequency of a specific type determine the date.
Examples: Painted Grey Ware (PGW), Northern Black Polished (NBP) ware, and Rouletted ware are markers of specific time ranges.
Technological Progress: The sequence of technology provides relative dates; for instance, copper technology consistently precedes iron technology.
Copper Hoard Culture: The Gangetic valley hoards are dated purely by typological analysis of objects like anthropomorphic figurines and harpoons.
Dressel’s Typology: Heinrich Dressel (1899) classified Roman amphorae by shape and texture. This remains a classic example of typological dating.
Dressel’s Classification of Roman Amphorae
Type 1: Roman wine amphora (129 BCE – 13 CE).
Type 2: Roman wine amphora (16 CE – 29 CE).
Type 3: Roman wine amphora (28 CE – 146 CE).
Type 4: Roman wine amphora (4 BCE – 24 CE).
Type 5: Roman wine amphora (Holotype, 12 BCE).
Type 6: Roman wine amphora (Holotype, 36 CE).
Types 7–11: Betic amphora for salted fish (Hispanic).
Type 12: Betic amphora for salted fish (Andalusia).
Types 13–15: Betic amphora for salted fish.
Type 20: Betic oil amphora ( century CE).
Types 26–27: Amphora ($3^{rd}$ century CE and later).
Relative Dating of Bones
Bones are critical organic samples for reconstructing dietary patterns, palaeo-climate, trade networks, and ancient rituals.
Fluorine Test:
Ground water contains small amounts of fluorine ions.
These ions combine with the hydroxyapatite crystals in the bone to form fluorapatite.
As time passes, the amount of fluorapatite increases; bones buried for longer periods have higher concentrations.
Nitrogen Test:
Bones consist of calcium phosphate, fat, and collagen (bone protein).
Upon death, collagen decays into nitrogen at a relatively uniform rate.
Because the rate of decay depends on the specific chemical and physical composition of the soil, it is not a universal constant but can be used to compare bones from the same deposit or burial.
Geochronology and Environmental Dating
Geochronology: Dating artifacts through their association with geological formations or processes, such as glacial movements or sea-level fluctuations.
Pleistocene Period (Ice Age): This period affected river action and sea levels, resulting in river terraces and coastal beds.
Example: Palaeolithic tools in the Soan valley, Punjab, are dated based on river terrace deposits.
Varve Analysis:
Established by Baron Gerard de Geer in the 1870s.
In still water bodies (lakes), summer meltwater deposits coarse silt, while winter ice cover allows fine clay to settle.
A pair of coarse and fine layers constitutes a "varve," representing one year.
The thickness of varves varies based on glacial discharge, creating a sequential landmark. The Scandinavian varve sequence is the most famous.
Deep-Sea Cores:
Ocean bed cores contain shells of foraminifera (microscopic marine organisms).
The shells are made of calcium carbonate. Scientists analyze the ratio of two oxygen isotopes in the carbonate to indicate sea temperature at the time the organisms lived.
Presence of foraminifera in inland soil indicates former sea extensions. S. R. Rao used this at the Lothal dockyard (Harappan), and Rajiv Nigam noted similar findings at Dholavira.
Ice-Sheet Cores: Extracted from the Arctic and Antarctic. They provide annual deposit records for the last 3,000 years, reflecting climatic oscillations.
Pollen Dating (Palynology):
Pollen grains are nearly indestructible and preserved in lake sediments.
Experts reconstruct vegetation and climate sequences (specifically Holocene sequences in Northern Europe).
Flotation Technique: Developed by Anthony J. Legge of Cambridge University to recover micro and macro botanical remains from soil samples.
Historical Dating and Palaeography
Historical Dating: Combines both absolute and relative methods.
Indian Eras for Absolute Dating: Ancient literate societies recorded dates using specific eras, including:
Saka era
Kaliyuga era
Vikrama era
Kollam era
Relative Historical Dating: Used for buildings (stupas, temples, mosques, churches, forts) and art (sculptures, icons) based on stylistic features.
Palaeography: Dating based on the evolution and style of scripts.
In India, over $100,000$ (one lakh) inscriptions have been documented on stone, copper, pottery, and ivory.
Brahmi Script: The ancestor of all Indian scripts.
Tamil-Brahmi Evolution: Developed into Vatteluttu script, then into the modern Tamil script.
Tamil-Brahmi duration: century BCE to $3^{rd}$ century CE.
Transformation to Vatteluttu: century CE.
Phases: Early, Middle, and Late (each roughly three centuries long).
Current statistics suggest of Indian inscriptions are dated via palaeography.