Historical sources on dating artefacts in archaeology

Extract A

"[Archaeologists] use relative and absolute dating methods. They use these methods to determine the age of sites, artifacts, and the behaviors they represent. Relative dating arranges past events in a sequence in relation to one another (think: earlier than, later than, more recent than, and so forth). Absolute dating attempts to pinpoint a [specific], known [period] in time such as a day, year, century, or millennia. Very few artifacts recovered from an [archaeological] site can be absolutely dated." 

Extract B

"Stratigraphy [is a Relative dating method] ... Layers of earth and other materials built over time. The Law of Superposition holds that, when undisturbed, deeper layers are older than the ones above them." 

Extract C

"Thermoluminescence [is an Absolute dating method] ... Used for rocks, minerals, ceramics and burned features, TL is based on the fact that almost all natural minerals [give off] light when heated. Energy absorbed from [natural] radiation frees electrons to move through the crystal [structure] and some are trapped at [weak points]. In the lab, samples are heated releasing the trapped electrons and producing light." 

Contextual information:

This article was published by the United States National Park Service as part of its Archeology Program, which educates the public about how archaeologists study and protect historic sites on federally managed land. The NPS is a government agency within the U.S. Department of the Interior, and this page provides an accessible overview of every major dating technique used by professional archaeologists today. 

Bibliographical reference:

National Park Service. (2023, May 9). How do archeologists date sites and artifacts? U.S. Department of the Interior. https://www.nps.gov/articles/000/how-do-archeologists-date-sites-and-artifacts.htm 

Copyright: This is a United States government work and is in the public domain under 17 U.S.C. § 105, which states that copyright protection is not available for any work of the United States Government. 

Extract A

"Relative Dating techniques can be used to find out if one culture is older or younger than another, but these techniques do not give a specific year. The famous Kelly [archaeological digs] conducted here at Ocmulgee used a relative dating technique called stratigraphy. In stratigraphy, an [archaeologist] observes the soil stratum (layer) where artifacts are found. Deeper [layers] mean older artifacts, rocks, or fossils." 

Extract B

"Absolute Dating means that the technique used can give an age in years. Physicists use radiocarbon dating to measure the amount of radioactive carbon (C14) in pieces of organic material such as bone, wood, or shell found at [archaeological] sites. When something dies, it begins to lose radioactive carbon. The smaller the amount found, the older the artifact. The physicist can give the [archaeologist] a date (plus or minus 200 years) for the artifact tested. One helpful tool for physicists is the [accelerator mass spectrometer], which counts carbon in small samples and allows artifacts to be dated more accurately than the [standard] radiocarbon method used before the 1980s." 

Extract C

"Radioactive Dating methods are the most widely used and accepted absolute dating methods. They are based on the natural radioactivity of certain minerals found in rocks. The rate of radioactive decay of particular [types of atoms] is known so the age of a [sample] can be [worked out] from the remaining radioactive material and its decay products." 

Contextual information:

This brochure was produced by the National Park Service for visitors to Ocmulgee Mounds National Historical Park in Georgia, one of the most significant archaeological sites in the southeastern United States. The site preserves evidence of over 17,000 years of continuous human [living], and the "Kelly excavations" referenced in the brochure were the famous 1930s–1940s government-funded digs directed by archaeologist Arthur R. Kelly. 

Bibliographical reference:

National Park Service. (n.d.). Archaeology: Our window to the past [Brochure]. U.S. Department of the Interior, Ocmulgee Mounds National Historical Park. https://www.nps.gov/ocmu/learn/historyculture/upload/Accessible-Archaeology-Updated.pdf 

Copyright: This is a United States government work and is in the public domain under 17 U.S.C. § 105.

"These rocks are stratified, or divided into [separate] layers, or strata. The term stratum means simply a bed, or any thing spread out or strewed over a given surface; and we [believe] that these strata have been generally spread out by the action of water, from what we daily see taking place near the mouths of rivers, or on the land during [floods]. For, whenever a running stream charged with mud or sand, has its [speed] checked, as when it enters a lake or sea, or overflows a plain, the sediment, previously held [up] by the motion of the water, sinks, by its own gravity to the bottom. In this manner layers of mud and sand are thrown down one upon another." 

Contextual information:

Sir Charles Lyell (1797–1875) was a Scottish geologist whose works established the foundations of modern geology, and whose ideas about the Earth changing slowly over time profoundly influenced Charles Darwin. The Student's Elements of Geology was his final major textbook, written as an accessible introduction for beginners, and this passage explains the fundamental principle behind stratigraphy: that layers of sediment build up over time, with each new layer sitting on top of older ones. 

Bibliographical reference:

Lyell, C. (1878). The student's elements of geology (p. 2). Harper & Brothers. https://www.gutenberg.org/files/3772/3772-h/3772-h.htm (Original work published 1871) 

Copyright: Public Domain.

Extract A

"Besides the [ability to tell apart different] sites there is a [large] subject in the [ability to tell apart different] objects and of styles. The first [necessary skill] of a digger — his archaeological experience — consists in [telling apart] the differences between products of various dates. An Egyptian copper adze [a type of hand tool] of the ages of middle prehistoric, late prehistoric, early dynastic, IIIrd, VIth, XIIth, or XVIIIth Dynasties can be told at a glance, and we only need more dated examples to be able to separate them still more finely. A cutting-out knife, a pair of tweezers, a comb, can be dated almost as certainly. But it is when we can look not only to differences of form, but also to variations of colour and texture, that we have the widest scope for [telling them apart]." 

Extract B

"Pottery is, however, the greatest resource of the [archaeologist]. For variety of form and texture, for decoration, for rapid change, for its quick fall into [being forgotten], and for its [incredible amount], it is in every respect the most important material for study, and it [makes up] the essential alphabet of archaeology in every land. Think for a moment how few people know the appearance of a common jug a century old, how the [pots] of Georgian times have all vanished, and new forms are made. Even of decorated china not one piece in a thousand in England is before the last century, and not one in a million is three centuries old; so rapidly does breakable ware [disappear], and become unknown." 

Contextual information:

Sir William Matthew Flinders Petrie (1853–1942) is widely regarded as the father of modern scientific archaeology, and he held the first Chair of Egyptology at University College London. He invented "sequence dating" in 1899 while studying 900 predynastic graves at Naqada in Egypt, where he classified pottery by its form and decoration and arranged the types into a chronological order — the method now known as typology. Methods and Aims in Archaeology (1904) was the first comprehensive textbook on archaeological field methods ever published. 

Bibliographical reference:

Petrie, W. M. F. (1904). Methods & aims in archaeology (pp. 14–16). Macmillan and Co. 

Copyright: Public Domain.

Extract A

"In an educational museum, [items] should be selected that are useful in displaying sequence. These should be arranged so as to show how one form has led to another. When there is actual evidence of the dates of the objects, of course the arrangement must be for the most part in the order of dates. But when, as in the case of most prehistoric objects and many of the arts of savage nations, the dates cannot be given, then [we] must [use] the sequence of type, and that is what I term 'Typology'. It is not an accepted term, and I am not aware that it has been applied before to the study of sequence of the types of the arts. But it appears to me that a name is wanted for this branch of investigation, which the term 'Typology' supplies." 

Extract B

"[Typology] includes the growth, varieties, and developments of the [different] types. It supplies the want of dates by showing how certain forms must have [come before] or followed others in the order of their development, or in the sequence of their [use]. It may be said, as a rule, that simple forms have [come before more detailed] ones. Within certain limits this must be true, but it is not always the case, for, in many instances, progress consists in [removing] [unnecessary detail], and reducing the [amount] of time and labour." 

Contextual information:

Lieutenant-General Augustus Henry Lane Fox Pitt-Rivers (1827–1900) was a British Army officer, ethnologist, and archaeologist who is credited with coining the term "typology" as it applies to archaeology. His interest in classifying artefacts by their form grew out of his professional work testing rifles for the British military in the 1850s, which led him to study how all objects made by humans gradually change over time. He donated his collection to the University of Oxford, where the Pitt Rivers Museum (established 1884) still displays objects arranged by type and function today. 

Bibliographical reference:

Pitt-Rivers, A. H. L. F. (1891). Typological museums, as exemplified by the Pitt-Rivers Museum at Oxford, and his provincial museum at Farnham, Dorset. Journal of the Society of Arts, 40, 115–117. 

Copyright: Public Domain.

Extract A

"The science of dendrochronology can be used to [work out] when a tree was [cut down] or naturally died, if the calendar year dates of tree growth rings can be determined. A tree's annual growth changes throughout the year in response to seasonal climate changes. At the beginning of each growing season, a layer of thin-walled cells called earlywood grow between the older wood and outer bark. As growth slows toward the end of summer, smaller, thicker-walled cells known as latewood are produced; and these usually appear darker in [colour] in a tree cross-section. Combined with cells formed during the normal growing season, these two cell types [make up] one annual ring representing one year of growth." 

Extract B

"Tree rings are important [records] when one considers that trees often live for hundreds of years and therefore, may contain a long record of environmental conditions. Matching tree ring width patterns in living and well-preserved dead trees can be [compared] among different tree ring series and tree ring [timelines] extending far beyond the range of living trees [can] be [put together]. This process, called crossdating, is the [basic] principle of dendrochronology and allows the [accuracy] necessary to help date [archaeological] sites." 

Contextual information:

This article appeared in Yellowstone Science, the official science publication of Yellowstone National Park, and was written by Dan Eakin and Elizabeth Horton to explain how tree-ring dating works and how it is used by archaeologists in the field. The science of dendrochronology was pioneered by astronomer A. E. Douglass (1867–1962) at the University of Arizona, who developed the method in the 1910s–1920s while studying connections between the sun's activity and climate patterns on Earth. 

Bibliographical reference:

Eakin, D., & Horton, E. (2019, April 10). Dendrochronology: The study of tree rings. Yellowstone Science, 26(1). National Park Service. https://home.nps.gov/articles/archeology-dendrochronology.htm 

Copyright: This is a United States government work and is in the public domain under 17 U.S.C. § 105.

Extract A

"The rate of decay is [easily] expressed in terms of an [atom type's] half-life, or the time it takes for one-half of a particular radioactive [atom type] in a sample to decay. Most radioactive [atom types] have rapid rates of decay (that is, short half-lives) and lose their radioactivity within a few days or years. Some [atom types], however, decay slowly, and several of these are used as geologic clocks." 

Extract B

"Another important atomic clock used for dating purposes is based on the radioactive decay of the [atom type] carbon-14, which has a half-life of 5,730 years. Carbon-14 is produced [all the time] in the Earth's upper atmosphere as a result of the [hitting] of nitrogen by neutrons from cosmic rays. This newly formed radiocarbon becomes [evenly] mixed with the nonradioactive carbon in the carbon dioxide of the air, and it eventually finds its way into all living plants and animals. In effect, all carbon in living organisms contains a constant [amount] of radiocarbon to nonradioactive carbon. After the death of the organism, the amount of radiocarbon gradually decreases as it [changes back] to nitrogen-14 by radioactive decay. By measuring the amount of radioactivity remaining in organic materials, the amount of carbon-14 in the materials can be calculated and the time of death can be determined. For example, if carbon from a sample of wood is found to contain only half as much carbon-14 as that from a living plant, the estimated age of the old wood would be 5,730 years." 

Extract C

"The radiocarbon clock has become an extremely useful and [effective] tool in dating the important [events] in the recent prehistory and history of man, but because of the relatively short half-life of carbon-14, the clock can be used for dating events that have taken place only within the past 50,000 years." 

Contextual information: This publication is part of the U.S. Geological Survey's General Information Product series, which is designed to explain earth science concepts to the general public. William L. Newman wrote the original booklet in 1977, and the online version was updated in 1997. The USGS is the United States' primary scientific agency for the study of the Earth, and its publications are among the most authoritative government sources on geological dating methods. 

Bibliographical reference:

Newman, W. L. (1997). Geologic time (Online ed.). U.S. Geological Survey General Information Product. https://pubs.usgs.gov/gip/geotime/radiometric.html 

Copyright: This is a United States government work and is in the public domain under 17 U.S.C. § 105.

"Thermoluminescence dating is used for rocks, minerals, ceramics and burned features. It is based on the fact that almost all natural minerals are thermoluminescent — they [give off] light when heated. Energy absorbed from [natural] radiation frees electrons to move through the crystal [structure] and some are trapped at [weak points]. In the lab, samples are heated releasing the trapped electrons and producing light. The light is measured to determine a date. Thermoluminescent dating is used to date [archaeological deposits], [identify fake] ceramics in art collections, and even date burned flint artifacts." 

Contextual information:

This text comes from the National Park Service's Archeology for Interpreters educational programme, which was developed to train park rangers and the public in understanding archaeological methods used at nationally protected sites across the United States. The thermoluminescence section specifically references fieldwork conducted at Hopewell Culture National Historical Park in Ohio, where archaeologists collected ceramic samples for TL dating. 

Bibliographical reference:

National Park Service. (n.d.). Archeology for interpreters: Thermoluminescence dating. U.S. Department of the Interior, National Park Service Archeology Program. https://www.nps.gov/archeology/AFORI/howfig_abs2.htm 

Copyright: This is a United States government work and is in the public domain under 17 U.S.C. § 105.