Dating techniques are procedures used by scientists to determine the age of rocks, fossils, or artifacts. Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide an approximate date in years. The latter have generally been available only since Many absolute dating techniques take advantage of radioactive decay , whereby a radioactive form of an element decays into a non-radioactive product at a regular rate. Others, such as amino acid racimization and cation-ratio dating, are based on chemical changes in the organic or inorganic composition of a sample. In recent years, a few of these methods have come under close scrutiny as scientists strive to develop the most accurate dating techniques possible. Relative dating methods determine whether one sample is older or younger than another.
Then, they use contextual clues and absolute dating techniques to help point to the age of the artifacts found in each layer. Learn how archaeologists dated the earliest metal body part in Europe. Objects can be grouped based on style or frequency to help determine a chronological sequence.
Relative dating has its limits. For a more precise date, archaeologists turn to a growing arsenal of absolute dating techniques. Perhaps the most famous absolute dating technique, radiocarbon dating was developed during the s and relies on chemistry to determine the ages of objects. Its inventor, Willard Libby, eventually won a Nobel Prize for his discovery.
The tibia bone of Australopithecus anamensis provided firm evidence that hominins walked upright half a million years earlier than previously thought. Thermoluminescence dating measures how many years have elapsed since the heating of a material containing a crystalline mineral. The technique can provide dates for sediments, ceramics, and other materials. Dendochronologythe study of tree rings, can date wooden structures or objects.
A variety of other chemistry-based techniques can also be used. In some cases, archaeologists also find dates written on objects or recorded in historical records to provide absolute dates. Discover how researchers figured out when pre-historic footprints were left in Canada. Absolute dating has its drawbacks: Techniques can be expensive and provide less clarity than their name might suggest. Radiocarbon dating, for example, can only be performed on objects younger than 62, years old, only results in date ranges, and can be thrown off when objects come into contact with younger organic material.
Relative and absolute dating techniques are often combined, as when a historical chronicle or pottery style is used to provide a more precise date for an object that has been placed within a year range by a chemical technique.
Interestingly, Hisarlik could be the site of Homeric Troy circa B. Invented by preeminent archaeologist Sir William Flinders-Petrie in the late nineteenth century, seriation, another form of relative dating, is based on the idea that over time artifacts such as gravestones and ceramics undergo changes in style, characteristics and use. Seriation is particularly useful when layers of strata are not available, such as at ancient cemeteries. The first and simplest method of absolute dating, chronological markers pertain to artifacts with dates inscribed upon them, such as coins, documents or inscriptions on buildings announcing historical events.
Roman coins are excellent for this usage, as they often show dates, as well as the likeness of the emperor in power when the coins were minted.
The only problem with this dating method is that when these markers are discovered out of context, their value is greatly diminished. Dendrochronology or tree-ring dating was developed in the early s by Tucson astronomer A. Douglasswho hypothesized that the growth rings in trees are influenced by solar flares and sunspot activity. This theory turned out to be true, of course, because solar activity affects virtually every living thing on the planet.
These growth rings can be used to date slices of wood or logs, sometimes to the exact calendar year. The limitation with this method is that growth rings only pertain to the climate in a particular region; thus, comparing growth rings from different areas is often useless.
Also, some trees show no growth rings.
In archaeology, timing is everything
Nevertheless, the International Tree Ring Database has contributions from 21 countries, providing researchers with comparative regional data. The development of radiocarbon dating in the s started a scientific revolution. The scientific basis of radiocarbon dating is that every living organism contains carbon and absorbs the radioactive isotope carbon C14 from the atmosphere during its life cycle. C14 forms by the bombardment of cosmic rays from space.
When the organism dies, the C14 begins to decay at a rate that appears constant. The half-life of this decay is about 5, years. Thus the age of the organism when it died can be calculated with great accuracy. This dating method remains accurate for about 57, years.
Also, since the advent of the Industrial Revolution, the amount of carbon spewed into the atmosphere has increased dramatically. More carbon, means more C Therefore, refinements and calibrations of the technique are a constant concern. Potassium-argon dating, like radiocarbon dating, involves the decay of radioactive elements in a sample. It is based on the decay of an isotope in potassium which then forms the element argon. Potassium is found in material such as micas, clay minerals, tephra and evaporates.
Potassium-argon dating is mostly limited to dating volcanic materials at sites between 50, and two billion years old.
This technique has been used greatly at Olduvai Gorge in Africa, helping date the hominid fossils found there. A recent modification is argon-argon dating, which has been used at sites such as Pompeii.
One of the oldest and most reliable radiometric dating methods, uranium-lead dating is used to date rocks from one million years to 4. Working best with rocks containing the mineral zircon or zirconium silicate, which is often used as a substitute for diamond, this method measures the level of lead in the zircon, as its uranium and thorium atoms shed alpha and beta particles and thereby decay into lead.
In fact, any lead found in zircon is a product of radiometric decay. Lead-lead dating is another method that can be used; it measures the level of isotopes in lead, the measurements of which can be used for dating very old rocks. Fission track dating was developed in the mid s.
This method is based on the knowledge that damage tracks in minerals and glasses are created when small amounts of uranium are present in a sample. Such damage tracks are accumulated at a fixed rate that can be measured. This dating method has been used at hominid fossil sites such as Zhoukoudian in China, where Peking Man - later labeled as a specimen of Homo erectus - was discovered in the s.
Obsidian is a volcanic glass used by early ancestors of man primarily during the Paleolithic era. Once obsidian is exposed to the air, such as after it was used to make spear points, arrowheads or knives, it begins to absorb water.
The resultant rim or rind can be measured using many different techniques such as microscopic depth profiling or, the most sensitive of the options, secondary ion mass spectrometry.
Mar 17, Dating refers to the archaeological tool to date artefacts and sites, and to properly construct history. All methods can be classified into two basic categories: a) Relative dating methods: Based on a discipline of geology called stratigraphy, rock layers are used to decipher the sequence of historical geological events. Relative techniques can determine the sequence of events but not the precise date of an event, making these methods Author: Johnblack. Dating Techniques Relative dating. Relative dating methods determine whether one sample is older or younger Stratigraphy. Stratigraphy is the study of layers of rocks or the objects embedded within those Seriation. Seriation is the ordering of objects according to their age. Faunal dating. Nov 20, Until this century, relative dating was the only technique for identifying the age of a truly ancient object. By examining the object's relation to layers of deposits in the area, and by comparing Author: Ben Mauk.
Thus, the larger the rind, the longer the artifact has been exposed to the air. Unfortunately, some factors can change the hydration rate of an obsidian artifact. The higher temperatures experienced at lower elevations, differences in water vapor pressure, and the intrinsic qualities of various obsidian samples can alter the hydration rate. Thermoluminescence TL is used for dating inorganic material, particularly pottery or other ceramics, hallmarks of ancient civilization from Mesopotamia to the Americas.
TL can also be used to date sediments.
Jun 01, This happens at known rates. By measuring the proportion of different isotopes present, researchers can figure out how old the material is. Here are some of the most common radiometric methods: Radiocarbon dating: Sometimes called carbon dating, this method works on organic material. Both plants and animals exchange carbon with their environment until they jankossencontemporary.com: Gemma Tarlach. Jun 28, Radiocarbon dating, for example, can only be performed on objects younger than 62, years old, only results in date ranges, and can be thrown off . Radiocarbon dating also know as carbon dating or carbon dating is a method of determining the age of an object containing organic material, this technique .
Invented by physicists aroun TL operates on the principle that when ceramics are heated, electrons are trapped in the minerals of the material. When this material is then re-heated in the laboratory the electrons in the minerals emit light or luminesce. This light is then measured to find the date the ceramic was fired or when sediment was exposed to sunlight.
The effectiveness of TL is from toyears. Unfortunately, this dating technique is not infallible. If a particular pottery vessel has been subjected to heat more than once, the resultant TL data can be inaccurate. Optically stimulated luminescence OSL measures the complex process when minerals in sediments are exposed to sunlight, which frees electrons trapped within the mineral lattice.
When the amount of electrons is measured, dating is accomplished. This method primarily dates sediments containing minerals such as quartz, feldspar and calcite.
OSL is often used in conjunction with thermoluminescence. Like thermoluminescence, rehydroxylation RHX is used to date ceramics. According to scientific observation, once a ceramic is fired it immediately begins to absorb moisture from the atmosphere at a measurable rate - the fourth root of the time elapsed since firing, actually. To test a sample, it is weighed and then heated to degrees Celsius until it is completely dehydrated.
Then the amount of water loss can be measured, showing the age of the ceramic. The drawback to RHX is that scientists need to know the temperature history of the site where the ceramic is found. Also, natural events such as wild fires could completely dehydrate a sample, thereby resetting its clock. Paleomagnetism PM is the study of the magnetic history of rock samples.
This magnetic orientation through millennia can be measured in rocks. Lead is another element that tends to absorb water and oxygen from the atmosphere over time.
FOSSILS: how fossils are dated
When a sample of lead is subjected to cryogenic temperatures it becomes a superconductor, but its level of corrosion from water and oxygen cause it to lose some of its superconductivity. This difference in conductivity can be measured with some accuracy. Dating lead is useful to archaeologists because it was widely used in antiquity, particularly in places such as ancient Israel and the Roman Empire.
Also known as racemization dating, amino acid dating relies on the principle that all biological tissues contain amino acids. But after the organism dies, the ratio of D to L tends to even out over time, a process known as racemization, and this tendency toward equilibrium can be measured.
However, racemization tends to happen more quickly in warm, wet climates, so knowing the climate history of the area where the artifacts were found is a critical issue. Acidity and alkalinity can also affect racemization.
Amino acid dating is accurate from 5, to one million years ago. Oxidized carbon ratio OCR dating is used to date organic material going back 35, thousand years. This dating method is based on the measurable difference between oxidizable and organic carbon.
Over time carbon tends to oxidize with exposure to the atmosphere. Dating is achieved by measuring the difference between the oxidizable and organic carbon. Please be advised that the OCR method is considered experimental and is therefore subject to further testing, evaluation and refinement.
Of course, this could be said of many dating methods! At present, most scientists opt for C dating instead. The advantage to such dating is that layers of volcanic ash are easy to spot and spread over a wide area. The device used to read the chemical composition of the tephra is an electron microprobe. The limitation of TC is that tephra chemistry, especially that of basaltic tephra, can be altered over time.
This technique has been used at Mt. Vesuvius in Italy and the island of Santorini near Crete, where a volcanic eruption in B. Oxygen isotope chronostratigraphy relies on the fact that oxygen has three different stable isotopesthe ratio of which changes over time and therefore can be dated in the rocks present in any particular area.
This ratio changes during long cold or warm periods of time, helping scientists learn more about the climate in which people may have lived.
Methods of dating old material
Uranium and thorium are radioactive elements that accumulate in some rock formations. Scientists use a mass spectrometer to measure the ratio between uranium and thorium, thereby establishing a date the radioactive breakdown began in both elements. This technique has been used to date rock formations found in caves, especially speleothems such as stalagmites and stalactites, some of which may have formed in the recent past, just thousands of years ago.
Many cave dwellers lived in these caves during the Pleistocene, when sea levels were hundreds of feet lower than present times. One of many non-destructive analytical dating methods, x-ray diffractometry, aka x-ray crystallography, is a technique that scatters x-rays over objects and substances, which can determine the arrangement of atoms and molecules in the crystals of both organic and inorganic material, which could include salts, metals, minerals and thin films.
This process can reveal information about the chemical composition and physical properties of such matter, including the structure of its DNA, if present. This technique can be used when the teeth of deceased animals or humans are extant. Assessing the age at death, as well as the season at death of the animal or person, cementochronology CC involves the analysis of the dental cementum deposits found attached to the root of a tooth.
Similar to the rings of trees, these deposits have rings showing annual growth, which can help scientists date skeletal remains and their contextual cts. Used by scientists since the s, CC, a form of bioarchaeologyis now used by forensic and physical anthropologists. Sign in or sign up and post using a HubPages Network account. Comments are not for promoting your articles or other sites. Hey, Asth, scientists use all of the aforementioned techniques for dating cities, particularly stratigraphy and artifact sequencing.
A lot depends on the location of this hypothetical city and its apparent age. Hey, James Walton, nobody has found any artifacts older than 15, years in the Americas. If you think you have, then call National Geographic or "60 Minutes.
Thanks for the comment, rehman. I wish I could tell you what to do about that artifact you mentioned, but I can't.
Your friend needs to ask an archaeologist or perhaps somebody who teaches archaeology or anthropology at the local college or university. Good luck.
A friend has emailed me image of an artifact claimed to be ancient. He asked me to have it assessed. Wonder if you can guide me on how should i go about it? WOW Kosmo, what cool facts and details about how do Archaeologist date events from the past.
Cool, very cool indeed, makes me wanta go back to school. Thanks for the kind words, Seeker7.