Archaeological methods: stratigraphy, typology, dating techniques, remote sensing

Intuition Beginner

Archaeologists reconstruct past lives from what people left behind — stone tools, pottery, food remains, bones, buildings, and garbage. They do not dig randomly. Survey comes first: walking across a landscape to find sites and map their distribution. Excavation follows, done carefully with trowels and brushes, recording the exact location of every artifact. The material record is the only direct evidence for most of human history.

The key principle is stratigraphy. In undisturbed deposits, deeper layers are older. By mapping these layers — called strata — archaeologists build relative chronologies that order events without assigning calendar dates. A layer of charcoal below a layer of pottery means the fire predates the pottery. This law of superposition, borrowed from geology, is the foundation of all relative dating in archaeology.

To get actual dates, archaeologists use absolute dating. Radiocarbon (C-14) dating measures the decay of carbon-14 in organic material — bone, charcoal, wood — and works back about 50,000 years. Dendrochronology, or tree-ring dating, can be precise to the year, but only works in regions with long tree-ring sequences. These methods turn relative sequences into calendar chronologies.

New technologies have transformed how archaeologists find sites without digging. LiDAR — lasers mounted on aircraft that penetrate forest canopy — has revealed entire buried cities in the Amazon and the Maya lowlands without touching the ground. Satellite imagery, ground-penetrating radar, and aerial photography extend the same idea: see beneath the surface before you excavate. What once took decades of survey can now be mapped in weeks.

Visual Beginner

The table below organises the four method families covered in this unit. Each family answers a different question about the past.

Method family	Core question	Key examples	Main limitation
Stratigraphy	Which layer is older?	Law of superposition, Harris matrix	Disturbed deposits break the sequence
Typology	How do styles change over time?	Seriation, sequence dating	Assumes gradual, directional change
Absolute dating	How old is this in calendar years?	Radiocarbon, dendrochronology, TL	Each method has a limited date range
Remote sensing	What lies beneath without digging?	LiDAR, GPR, satellite imagery	Requires ground-truthing by excavation

Dating method	Material dated	Typical range	Precision
Radiocarbon (C-14)	Organic material (bone, charcoal, wood)	Up to ~50,000 years	Decades to centuries after calibration
Dendrochronology	Wood with preserved rings	Up to ~12,000 years	Exact year, in regions with master sequences
Thermoluminescence (TL)	Heated flint, pottery	100–500,000 years	~10% of age
OSL	Sun-exposed sediment	Up to ~300,000 years	~5–10% of age
K-Ar / Ar-Ar	Volcanic material	100,000–billions of years	Good for very old sites

Worked example Beginner

Example 1: Reading a Harris matrix

A trench reveals three layers and one cut. Layer C is the deepest deposit. Layer B lies on top of C. Layer A sits on top of B. A later pit (Feature P) was dug down through A and B, destroying part of both. The Harris matrix records: C is below B, B is below A, and P cuts A and B. Reading the diagram, the sequence is C, then B, then A, then P. The cut disrupts the simple "deeper is older" rule because P, though deep, is the youngest feature.

Example 2: Radiocarbon in practice

A charcoal sample from a hearth is sent to a lab. Living organisms absorb carbon-14 from the atmosphere while alive; after death, the isotope decays with a half-life of about 5,730 years. The lab measures how much carbon-14 remains. If the sample has about one eighth of the modern level, roughly three half-lives have passed, giving an age near 17,000 years.

But atmospheric carbon-14 has fluctuated over time, so the raw measurement is calibrated against tree-ring data. The calibrated result is reported as a range — for example, 16,800 to 17,400 years before present — with a stated probability. Accelerator mass spectrometry (AMS) needs only milligrams of carbon, so a single seed can now be dated.

Example 3: LiDAR over the Maya lowlands

Flying over the jungle of northern Guatemala, a LiDAR instrument fires hundreds of thousands of laser pulses per second. Most bounce off the canopy, but enough reach the ground to build a terrain model. Stripping away the trees digitally reveals causeways, pyramids, reservoirs, and house mounds hidden beneath the forest.

Surveys of the Mirador-Calakmul region documented thousands of previously unknown structures, implying that the Classic Maya built low-density urban sprawl far larger than anyone had estimated from ground survey alone. The discovery reframes Maya civilisation as one of the most populous and engineered of the ancient world.

Check your understanding Beginner

Formal definition Intermediate+

Survey and sampling

Archaeological survey is the systematic examination of a region to locate and record sites without excavation. Pedestrian survey — fieldwalkers spaced at fixed intervals walking transects and recording surface artifacts — is the most common form. Sampling strategies determine which parts of a landscape are examined: random sampling selects areas by chance; stratified sampling divides the region into zones (by geology, soil, or elevation) and samples each; systematic sampling covers regularly spaced transects or grid squares. Surface collection records the density and type of artifacts visible on the ground, and Geographic Information Systems (GIS) integrate the resulting spatial data into layered maps for analysis.

Excavation methods

The Wheeler-Kenyon method, developed by Mortimer Wheeler and Kathleen Kenyon, excavates a grid of vertical trenches separated by standing baulks that preserve the stratigraphic profile for reference. Each layer is removed separately and every find is recorded in three dimensions. Open-area excavation exposes large horizontal surfaces layer by layer, suited to sites where the spatial layout of a single period matters most. Provenience — the precise three-dimensional coordinate of every find — is recorded because context, not the object alone, carries the information.

The Harris matrix formalises stratigraphic recording. Each deposit, interface, and feature is a unit; arrows record relationships of overlay, underlie, equality, and cut. The resulting diagram is a directed graph encoding the relative sequence of every event at the site.

Stratigraphy and site formation

Stratigraphy rests on three geological principles. The law of superposition states that in an undisturbed sequence, lower layers predate upper ones. The principle of original horizontality holds that sediments are deposited roughly flat, so tilted layers were disturbed after deposition. The principle of lateral continuity holds that a deposit originally extended continuously until it thinned or was truncated.

Michael Schiffer distinguished cultural formation processes (C-transforms — discard, loss, caching, redeposition) from natural formation processes (N-transforms — erosion, bioturbation, colluviation). The archaeological record is not a passive reflection of past behaviour; it is transformed by both. Taphonomy studies the processes affecting organic remains after deposition — scavenging, weathering, trampling, and soil chemistry — that determine what survives and in what condition.

Key result: relative and absolute dating Intermediate+

Typology and seriation

Typology classifies artifacts into types defined by shared attributes — form, material, decoration, technology. Three approaches define types differently. Modal classification groups artifacts around a central tendency or ideal type. Paradigmatic classification defines types by the intersection of attribute states on orthogonal dimensions. Typological classification groups by overall similarity.

Seriation arranges assemblages in order based on stylistic change. In frequency seriation, the proportion of each type is plotted across assemblages; types wax and wane in popularity, producing battleship-shaped curves that order the assemblages chronologically. Occurrence seriation uses only the presence or absence of types. Sequence dating, devised by W. M. F. Petrie for Egyptian Predynastic graves, orders burials by the changing composition of their grave goods, establishing a relative chronology before any absolute dates existed.

Relative dating combines stratigraphy, typology, and cross-dating — comparing an assemblage to a known chronology elsewhere. A Mycenaean pot found in an Egyptian tomb of known date dates the tomb's other contents by association.

Absolute (chronometric) dating

Radiocarbon dating, developed by Willard Libby in 1949, exploits the decay of carbon-14 (half-life 5,730 years) in organic material. Accelerator mass spectrometry (AMS) counts individual carbon-14 atoms, needing only milligrams of carbon and enabling dating of a single seed or bone fragment. Raw dates must be calibrated against curves such as IntCal20, derived from tree-ring chronologies, because atmospheric carbon-14 has fluctuated. Marine reservoir effects — organisms in the ocean incorporate "old" carbon — and contamination must be corrected. The practical limit is about 50,000 years.

Thermoluminescence (TL) dates heated crystalline material (pottery, burnt flint) by measuring trapped electrons released as light when the sample is reheated in the lab; it dates the last firing, covering roughly 100 to 500,000 years. Optically stimulated luminescence (OSL) dates the last time sediment grains were exposed to sunlight, dating the burial of deposits directly.

Archaeomagnetism records the direction and intensity of the Earth's magnetic field preserved in fired features (hearths, kilns) when they cool; comparison with regional master curves dates the last firing. Dendrochronology matches the ring-width sequence of a timber sample to a master chronology; bristlecone-pine sequences extend over 9,000 years and anchor the radiocarbon calibration curve itself. Obsidian hydration measures the hydration rind that grows on a freshly flaked surface, providing a relative or calibrated age for obsidian artifacts.

For older deposits, uranium-series dating measures uranium isotope decay in cave carbonates (1,000–500,000 years); K-Ar and Ar-Ar dating date volcanic material from millions to billions of years and have anchored the chronology of East African hominin sites; and fission-track dating counts damage trails from uranium fission in uranium-bearing minerals.

Exercises Intermediate+

Advanced results: remote sensing, archaeometry, and theory Master

Remote sensing

Aerial photography launched archaeological remote sensing. O. G. S. Crawford, working in Britain in the 1920s, recognised that buried ditches and walls affect crop growth and soil colour, producing cropmarks, soil marks, and shadow marks visible from the air. The technique matured during and after World War I, when military aerial photography was adapted to archaeological survey.

Satellite imagery extended the view. Declassified CORONA intelligence imagery from the 1960s–70s preserves a snapshot of Near Eastern landscapes before modern development erased many sites. Landsat and commercial imagery, including multispectral and hyperspectral sensors, detect vegetation stress and soil anomalies associated with buried remains. Google Earth has enabled open-source discovery by both specialists and the public. Sarah Parcak's work in satellite archaeology has surveyed landscapes across Egypt and the Roman world at regional scale.

LiDAR (light detection and ranging) has been the most transformative recent technology. Airborne lasers penetrate forest canopy to produce bare-earth terrain models. At Caracol in Belize, LiDAR revealed terraces, causeways, and reservoirs spanning hundreds of square kilometres. At Angkor in Cambodia, it mapped urban neighbourhoods and canals beneath the jungle, showing that greater Angkor was the largest pre-industrial urban complex known. Surveys in the Mosquitia of Honduras and across the Amazon have revealed geoglyphs and earthworks implying dense pre-contact settlement. Jesse Casana's work has used satellite imagery and LiDAR to document the destruction of archaeological landscapes in Syria during conflict.

Ground-penetrating radar (GPR), advanced by Lawrence Conyers, maps buried features in three dimensions by radar pulses without excavation; performance depends on soil conductivity and moisture. Magnetometry detects burnt features, hearths, and pits; resistivity maps buried walls through moisture contrast; electromagnetic conductivity measures soil conductivity and magnetic susceptibility. These geophysical survey methods let archaeologists identify buried structures before a single trench is opened, prioritising excavation and preserving untouched deposits.

Underwater archaeology

George Bass's excavation at Cape Gelidonya (Turkey, 1960) established scientific underwater archaeology, recording a Bronze Age shipwreck with the same rigour as a land site. The field now uses mixed-gas diving, remotely operated vehicles (ROVs), and submersibles to reach deep wrecks. Submerged landscapes — Doggerland beneath the North Sea and Beringia between Asia and the Americas — preserve evidence of coastlines occupied during lower sea levels. Geoff Bailey has argued that coastals and submerged shelves were central, not peripheral, to human settlement. The anoxic waters of the Baltic preserve shipwrecks with intact hulls and cargo.

Archaeometry and material analysis

Archaeometry applies physical and chemical methods to artefacts. Neutron activation analysis (NAA) and X-ray fluorescence (XRF) — both portable and lab-based — determine elemental composition, enabling provenance studies that trace obsidian, ceramics, and metals to their geological source. ICP-MS measures trace elements at parts-per-billion sensitivity.

Stable isotope analysis reconstructs diet and migration. Strontium isotopes (${}^{87}$Sr/${}^{86}$Sr) in tooth enamel reflect the geology where a person grew up, identifying migrants (work by T. Douglas Price and others). Oxygen isotopes track climate and water source. Carbon and nitrogen isotopes in bone collagen distinguish marine versus terrestrial diets and C3 versus C4 plant consumption. Lead isotopes and proteomics source metals and identify proteins on artefacts.

The ancient DNA (aDNA) revolution, led by Svante Pääbo's sequencing of the Neanderthal genome and David Reich's Who We Are and How We Got Here, has rewritten population history. aDNA now recovers from soil and sediment (metagenomic sampling), detecting human and animal presence without bones. Lipid residue analysis (Richard Evershed) identifies dairy fats, plant oils, and tars absorbed in pottery walls. Starch grains and phytoliths recovered from tool surfaces and dental calculus record plant use; Christina Warinner's work on calcified dental plaque has reconstructed ancient diet and oral microbiomes.

Archaeological theory

Culture-historical archaeology, dominant in the early twentieth century, explained change through diffusion and migration, treating cultures as shared norms carried by peoples. Processual (New) archaeology, launched by Lewis Binford in the 1960s, demanded scientific method, explicit hypothesis testing, ecological and evolutionary models, middle-range theory linking material traces to behaviour, and ethnoarchaeology — studying living societies to build interpretive bridges.

Post-processual archaeology, associated with Ian Hodder's contextual archaeology and Michael Shanks and Christopher Tilley's interpretive programme, argued that material culture is actively meaningful, not a passive reflection of adaptation. Mark Leone developed critical archaeology exposing ideology in the material record. Feminist archaeology (Margaret Conkey and Joan Spector; Joan Gero and Conkey) challenged androcentric reconstructions. Indigenous archaeology (Joe Watkins) and community-based participatory archaeology (Sonya Atalay) reframe descendant communities as partners and co-researchers rather than subjects.

Public archaeology and cultural resource management

Cultural resource management (CRM) is the largest employer of archaeologists worldwide. In the United States, Section 106 of the National Historic Preservation Act requires federal agencies to consider the effects of their actions on historic properties, generating contract archaeology before development. NAGPRA (Native American Graves Protection and Repatriation Act, 1990) requires institutions to return ancestral remains and sacred objects to descendant communities, transforming museum and university practice. Looting and the illicit antiquities trade destroy context irreversibly and, in regions of conflict, fund armed groups; the destruction of heritage in Syria and Iraq by ISIS underscored the vulnerability of archaeological sites to ideological violence.

Connections Master

• Archaeology: material culture and excavation 31.03.01. This unit extends the foundational concepts of the preceding unit. Where 31.03.01 introduced artefacts, ecofacts, features, and the rationale for excavation, this unit covers the technical apparatus — stratigraphic recording, typological classification, chronometric dating, and remote sensing — that converts raw excavation and survey data into chronological and spatial knowledge.

• Biological anthropology and hominin evolution 31.04.01. Absolute dating methods, especially K-Ar and Ar-Ar dating of volcanic ash layers, anchor the chronology of early hominin sites in East Africa. Stable isotope and aDNA analyses bridge biological and archaeological evidence, linking skeletal morphology, diet, and migration to material culture.

• Linguistic anthropology 31.05.01. Where writing exists, inscriptions and tablets provide cross-dating anchors for archaeological sequences. Decipherment of scripts (cuneiform, hieroglyphic, Maya glyphs) depends on archaeological context for dating, while the texts themselves illuminate the material record.

• Cultural anthropology and ethnography 31.02.01. Ethnoarchaeology applies ethnographic observation of living societies to build middle-range theory linking behaviour to material traces, addressing the inferential gap between what people do and what survives in the ground.

• Geology and earth science [27]. Stratigraphy, superposition, and lateral continuity are geological principles. Geoarchaeology, tephrochronology, and sediment analysis apply earth-science methods to site formation, while volcanic ash layers and palaeomagnetic reversals provide dating frameworks.

• Statistics [26, 37]. Seriation, sampling design, spatial statistics, and radiocarbon calibration all rest on statistical reasoning — probability, least-squares fitting, and error propagation. Calibration curves and Bayesian chronological modelling are statistical constructions.

• History of science [33]. The development of radiocarbon dating by Libby, the aDNA revolution led by Pääbo, and the LiDAR surveys of the 2010s are case studies in how new measurement technologies reshape a discipline's questions and conclusions.

Historical and philosophical context Master

From antiquarianism to stratigraphic excavation

Archaeology emerged from antiquarian collecting in the nineteenth century. Christian Jürgensen Thomsen's Three-Age System (Stone, Bronze, Iron), organising the Danish National Museum's collections by the material of the artefacts, imposed a technological sequence on the past that proved to be chronological. Jacques Boucher de Perthes argued in the 1840s that stone tools found deep in river gravels predated any written record, forcing recognition of human antiquity against biblical chronologies. Charles Lyell's geological principles supplied the law of superposition and the method for reading stratigraphy.

General Augustus Pitt Rivers imposed systematic recording on British excavation in the late nineteenth century, insisting that every object — however mundane — be recorded in context and published. Mortimer Wheeler and Kathleen Kenyon systematised stratigraphic excavation in the mid-twentieth century through the grid-and-baulk method that bears their names. Edward C. Harris's 1973 Harris matrix gave stratigraphic recording a formal diagrammatic language that is now standard.

The radiocarbon revolution

Willard Libby's development of radiocarbon dating, published in 1949, was the most consequential methodological advance in the discipline's history. For the first time, prehistoric sites could be assigned absolute calendar dates independently of stylistic sequences. The early results were controversial: they showed that European megalithic monuments predated Egyptian pyramids, undermining diffusionist narratives that derived European culture from the Near East. The invention of AMS in the late 1970s reduced sample sizes from grams to milligrams, allowing individual seeds and small bone fragments to be dated. Successive calibration curves (IntCal98, IntCal04, IntCal09, IntCal13, IntCal20) have refined the conversion of radiocarbon measurements to calendar ages.

The theoretical revolutions

Culture history dominated the early twentieth century, organising the past into cultures and explaining change through migration and diffusion. Lewis Binford's 1962 paper "Archaeology as Anthropology" launched processual (New) archaeology, demanding that the discipline adopt the scientific method, test explicit hypotheses, and search for general laws of cultural dynamics. Processualists drew on systems theory, ecology, and evolutionary theory, and developed ethnoarchaeology and middle-range theory to bridge the gap between static material remains and the dynamic behaviours that produced them.

Ian Hodder's post-processual critique of the 1980s argued that material culture is meaningful and active, not a passive reflection of adaptation, and that context determines meaning. This opened space for symbolic, structural, feminist, critical, and indigenous archaeologies, each challenging the positivist assumptions of processualism. The discipline today is pluralist: scientific dating and remote sensing coexist with interpretive and community-based approaches, and many projects combine both.

The remote-sensing and aDNA revolutions

The past two decades have seen two further revolutions. LiDAR, applied archaeologically from the late 2000s onward, revealed urban landscapes beneath tropical forests that decades of ground survey had missed, overturning population estimates for the Maya and Amazon. Ancient DNA, transformed by next-generation sequencing from 2010, has rewritten the population history of Eurasia, the Americas, and Africa, revealing migrations and admixtures invisible to artefact-based reconstruction. The synergy between aDNA, stable isotopes, and traditional archaeology defines the current frontier — but it also raises ethical questions about the sampling of ancestral remains and the governance of genetic data from descendant communities.

Bibliography Master

1. Renfrew, C. & Bahn, P., Archaeology: Theories, Methods and Practice, 7th ed. (Thames & Hudson, 2016). The standard methods textbook; Ch. 1–5 cover survey, excavation, stratigraphy, typology, and dating.

2. Kottak, C. P., Anthropology: Appreciating Human Diversity, 17th ed. (McGraw-Hill, 2019). Introductory four-field text; Ch. 4 introduces archaeological method for beginners.

3. Haviland, W. A., Walrath, D., Prins, H. E. L. & McBride, B., Cultural Anthropology: The Human Challenge, 15th ed. (Cengage, 2017). Ch. 4 surveys archaeology and its methods within a cultural-anthropology frame.

4. Taylor, R. E. & Aitken, M. J. (eds.), Chronometric Dating in Archaeology (Plenum, 1997). Authoritative reference on radiocarbon, TL, OSL, archaeomagnetism, obsidian hydration, and U-series methods.

5. Libby, W. F., Radiocarbon Dating (University of Chicago Press, 1952). The foundational monograph by the method's inventor.

6. Harris, E. C., Principles of Archaeological Stratigraphy (Academic Press, 1979). Introduces the Harris matrix and formalises stratigraphic recording.

7. Schiffer, M. B., Formation Processes of the Archaeological Record (University of New Mexico Press, 1987). Defines C-transforms and N-transforms and the framework for site-formation analysis.

8. Binford, L. R., "Archaeology as Anthropology," American Antiquity 28(2) (1962), 217–225. The manifesto launching processual (New) archaeology.

9. Hodder, I., Reading the Past: Current Approaches to Interpretation in Archaeology, 3rd ed. (Cambridge University Press, 2003). The clearest statement of contextual and post-processual archaeology.

10. Petrie, W. M. F., Diospolis Parva: The Cemeteries of Abydos (Egypt Exploration Fund, 1901). Introduces sequence dating for Egyptian Predynastic material.

11. Bass, G. F., "Excavating a Bronze Age Shipwreck," Archaeology 14(2) (1961), 78–87. Report on Cape Gelidonya, the first scientific underwater excavation.

12. Parcak, S., Satellite Remote Sensing for Archaeology (Routledge, 2009). Foundational textbook on satellite archaeology and multispectral survey.

13. Conyers, L. B., Ground-Penetrating Radar for Archaeology, 3rd ed. (Altamira, 2013). The standard reference on GPR method and interpretation.

14. Chase, A. F., Chase, D. Z., Weishampel, J. F., Drake, J. B., Shrestha, R. L., Slatton, K. C. & Awe, J. J., "Airborne LiDAR, archaeology, and the ancient Maya landscape at Caracol, Belize," Journal of Archaeological Science 38(2) (2011), 387–398. Landmark LiDAR study revealing Maya urban sprawl.

15. Pääbo, S., Neanderthal Man: In Search of Lost Genomes (Basic Books, 2014). First-person account of the Neanderthal genome project and the aDNA revolution.

16. Reich, D., Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past (Pantheon, 2018). Synthesis of population history from ancient DNA.

17. Evershed, R. P., "Organic residue analysis in archaeology: the archaeological biomarker revolution," Archaeometry 50(5) (2008), 895–924. Reviews lipid residue analysis of pottery.

18. Warinner, C., Rodrigues, J. F. M., Vyas, R., et al., "Pathogens and host immunity in the ancient human oral cavity," Nature Genetics 46 (2014), 336–344. Pioneering metagenomic study of dental calculus.

19. Price, T. D., Burton, J. H. & Bentley, R. A., "The characterization of biologically available strontium isotope ratios for the study of prehistoric migration," Archaeometry 44(1) (2002), 117–135. Foundational strontium-isotope provenance method.

20. Conkey, M. W. & Spector, J. D., "Archaeology and the Study of Gender," Advances in Archaeological Method and Theory 7 (1984), 1–38. Foundational paper of feminist archaeology.

21. Atalay, S., Community-Based Archaeology: Research with, by, and for Indigenous and Local Communities (University of California Press, 2012). Defines community-based participatory archaeology.

22. Watkins, J., Indigenous Archaeology: American Indian Values and Scientific Practice (AltaMira, 2000). Argues for integrating indigenous knowledge and perspectives.

23. Leone, M. P., "Archaeology and the Annapolis Renaissance," in The Recovery of Meaning, ed. Leone & Potter (Smithsonian Institution Press, 1988), 1–60. Foundational statement of critical archaeology.

24. Casana, J. & Panahipour, M., "Satellite-Based Monitoring of Looting and Damage to Archaeological Sites in Syria," Journal of Eastern Mediterranean Archaeology and Heritage Studies 6(1–2) (2018), 152–173. Remote-sensing documentation of conflict-driven site destruction.