Petrology Tulane University Prof. Stephen A. Nelson Radiometric Dating Prior to the best and most accepted age of the Earth was that proposed by Lord Kelvin based on the amount of time necessary for the Earth to cool to its present temperature from a completely liquid state. Although we now recognize lots of problems with that calculation, the age of 25 my was accepted by most physicists, but considered too short by most geologists. Then, in , radioactivity was discovered. Recognition that radioactive decay of atoms occurs in the Earth was important in two respects: It provided another source of heat, not considered by Kelvin, which would mean that the cooling time would have to be much longer. It provided a means by which the age of the Earth could be determined independently.
The half-life of the uranium to lead is 4. The uranium to lead decay series is marked by a half-life of million years. These differing rates of decay help make uranium-lead dating one of the most reliable methods of radiometric dating because they provide two different decay clocks.
This provides a built-in cross-check to more accurately determine the age of the sample. Uranium is not the only isotope that can be used to date rocks; we do see additional methods of radiometric dating based on the decay of different isotopes.
How Carbon Dating Works
For example, with potassium-argon datingwe can tell the age of materials that contain potassium because we know that potassium decays into argon with a half-life of 1. With rubidium-strontium datingwe see that rubidium decays into strontium with a half-life of 50 billion years. By anyone's standards, 50 billion years is a long time. In fact, this form of dating has been used to date the age of rocks brought back to Earth from the moon.
So, we see there are a number of different methods for dating rocks and other non-living things, but what if our sample is organic in nature? For example, how do we know that the Iceman, whose frozen body was chipped out of glacial ice inis 5, years old?
Well, we know this because samples of his bones and hair and even his grass boots and leather belongings were subjected to radiocarbon dating. Radiocarbon datingalso known as carbon dating or simply carbon dating, is a method used to determine the age of organic material by measuring the radioactivity of its carbon content.
So, radiocarbon dating can be used to find the age of things that were once alive, like the Iceman. And this would also include things like trees and plants, which give us paper and cloth. So, radiocarbon dating is also useful for determining the age of relics, such the Dead Sea Scrolls and the Shroud of Turin.
With radiocarbon dating, the amount of the radioactive isotope carbon is measured. Compared to some of the other radioactive isotopes we have discussed, carbon's half-life of 5, years is considerably shorter, as it decays into nitrogen Carbon is continually being created in the atmosphere due to the action of cosmic rays on nitrogen in the air.
Carbon combines with oxygen to create carbon dioxide. Because plants use carbon dioxide for photosynthesis, this isotope ends up inside the plant, and because animals eat plants, they get some as well. When a plant or an animal dies, it stops taking in carbon The existing carbon within the organism starts to decay back into nitrogen, and this starts our clock for radiocarbon dating.
A scientist can take a sample of an organic material when it is discovered and evaluate the proportion of carbon left in the relic to determine its age. Let's review. Radiometric dating is a method used to date rocks and other objects based on the known decay rate of radioactive isotopes. The decay rate is referring to radioactive decaywhich is the process by which an unstable atomic nucleus loses energy by releasing radiation.
Each radioactive isotope decays at its own fixed rate, which is expressed in terms of its half-life or, in other words, the time required for a quantity to fall to half of its starting value.
There are different methods of radiometric dating. Uranium-lead dating can be used to find the age of a uranium-containing mineral. Uranium decays to lead, and uranium decays to lead The two uranium isotopes decay at different rates, and this helps make uranium-lead dating one of the most reliable methods because it provides a built-in cross-check. Additional methods of radiometric dating, such as potassium-argon dating and rubidium-strontium datingexist based on the decay of those isotopes.
Radiocarbon dating is a method used to determine the age of organic material by measuring the radioactivity of its carbon content. With radiocarbon dating, we see that carbon decays to nitrogen and has a half-life of 5, years. To unlock this lesson you must be a Study. Create your account. Already a member? Log In. Did you know We have over college courses that prepare you to earn credit by exam that is accepted by over 1, colleges and universities.
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I am a student I am a teacher. Try Study. Cancel anytime. What teachers are saying about Study. Just checking in. Are you still watching? This is some of the most unreasonable shit I've ever heard! Even from a religious standpoint this makes no sense: What does this say about the idea of a perfect God with a perfect creation plan?
What was wrong with his original decay rate? Why did he not create it right the first time around? Did he just screw up and suddenly realize, 2, years in: "Ahh, fuck! I knew I was forgetting something! Why the second-guessing of himself? Why even bother with changing the decay rate-and why change it in such a way that creates the perfect misimpression that the earth and universe is much older than it actually is?
What could this be if not a massive campaign of deliberate, divine misinformation? And let's be clear about something: The only reason they're positing accelerated rates of decay is to try to square their holy book with the world around them.
Valuable information decay rate dating methods have removed
Young-earth creationists believe, on the basis of what they read in the Bible, that the Earth is 6, years old; this is the core reason that they try to undermine the validity of radiometric dating and this is why they go to the absurd length of positing accelerated rates of radiometric decay. They see the contradiction and conclude that the radiometric dating methods must be the problem-not their holy book-and they have this completely backwards.
Answers In Genesis writes that:. This is a pretty obvious case of trying to torture and contort the data into agreeing with your preconceived conclusions-as opposed to simply basing your conclusions off of whatever it is that the evidence shows. The special pleading in such claims is glaring. Why on Earth should the laws of physics change, just like that, so massively and so conveniently?
And it glares even more when you have to make mutually adjusted special pleading claims for each one of the clocks separately. Source: p. Even if we humor the creationist and imagine that something like this happened, more problems immediately dogpile onto the heap of stupidity before us. Jeff Zweerink outlines one of these problems on Reasons. How did Noah and his passengers survive a year in which radioactivity was one million times greater than it is today?
Shoulders down decay rate dating methods suggest
No known solution exists, they state. In the absence of the Biblical creation story, no sane scientist would even consider such an idea. But let's give the creationists some credit here: it's not all just fanciful speculation they're engaged in.
In fact, the RATE group claims to have scientific support for their views on accelerated decay rates, and at the very least, we can say this is a step up for creationists, because their usual research methodology consists of little more than reading the Bible and lamenting about sin. One piece of evidence cited is the detection of ancient carbon As we read on Answers In Genesis.
If these substances were really millions or billions of years old respectively, there should be no carbon left in them. Carbon has a half-life of 5, years. With the most accurate mass spectrometers, the oldest calculated age of items containing carbon is about 80, years. Diamonds are assumed to be many billions of years old and should contain no detectable carbon as it would have all decayed to nitrogen long ago. The same is true of coal which was supposedly deposited hundreds of millions of years ago, according to the evolutionary model.
The presence of carbon in these materials clearly supports the idea of a young earth as described by the Bible. Whenever we're confronted with an amazing claim like this, we should always ask ourselves: Could there be an alternative explanation for these findings? In the case of carbon in coal and diamonds, the answer is a firm "yes.
For example, neutrons from uranium decay can produce C from nitrogen impurities. The authors declare that since they used extraordinary care in handling the samples and are studying diamond, no extraneous source is possible. However, it is virtually impossible to eliminate such sources and chronologists discount the reliability of C dating if the concentration is below approximately 0. The RATE group also points to helium in zircon crystals as proof of accelerated rates of decay.
And yes, believe it or not, "zircon crystals" are a real thing. They sound like the fuel for a spaceship in a science-fiction novel or something! Answers In Genesis writes the following :. Zircon crystals in granite contain radioactive uranium, which decays into lead over time. As the uranium decays, helium is produced in the crystals.
Phrase simply decay rate dating methods agree with
Helium escapes from the crystals at a known, measurable rate. If those rocks were over a billion years old, as evolutionists claim, the helium should have leaked out of the rock. The presence of lots of helium in the crystals is evidence in support of a young earth. The diffusion chemistry expert Gary Loechelt has outlined a number of problems with their research methodology in an article on Reasons.
Once this error was corrected, the fraction of helium remaining in the zircon samples dropped considerably. In contrast, I used a geologically reconstructed thermal history that was highly non-uniform over time. This type of model ignores the possibility that helium atoms behave differently depending upon their location in the crystal, with atoms in the vicinity of defects moving more readily than those that are in the bulk crystal.
Instead, I incorporated a multi-domain diffusion model which takes this effect into account. What is the consequence of all these corrections? Even if the creationists were correct about the levels of helium, however, this wouldn't prove accelerated decay rates, because as Randy Isaac points outuranium-helium dating is no longer used or recommended by experts in the field:.
Not only do the scientific findings of the RATE group fall flat, but their general approach to science is also an embarrassment-which is not a surprise when you consider that they're young-earth creationists.
I don't know about you, but I wouldn't trust a young-earth creationist to make me a ham sandwich -let alone perform scientific research on as complex a subject as radiometric dating.
As we read on Wikipedia. One thing we can say in praise of the RATE group is that they actually do take peer review very seriously. As Randy Isaac writes. An appendix to this chapter, written by Henry Morris Jr. Criteria for selecting reviewers include, whenever possible, those who are in agreement with the biblical viewpoint of the researcher. So basically, these creationists' idea of peer review is intentionally selecting reviewers who already agree with the conclusion that they're setting out to demonstrate in their research.
This is the exact opposite of how science-and rational inquiry, generally-should be done: You should be seeking out the strongest challengers to test your ideas-not the most deferential supporters.
A user on who has since deleted his account made a great point about the general approach taken by creationists towards radiometric dating.
As this mystery user put it. They don't have one. The creationist technique is to simply discredit any finding or result that threatens their beliefs, all while refusing to provide any convincing or scientifically valid evidence for their own theories. It's also worth pointing out that even if creationists were correct when they argue that radiometric and other datings methods are unreliable, all this would demonstrate is that we simply don't know what the age of the Earth is-not that it's 6, years old.
What if the dating methods are inaccurate, but it turns out that the Earth is actually 50 billion years old, and the creationists are thus even further away from the correct date than we previously thought? Contrary to what creationists argue, radiometric dating methods are very reliable. This becomes crystal clear when multiple different dating techniques provide the exact same answer. Yes, there are specific circumstances where the tools give us the wrong answer-but the experts in the field are well aware of these limitations.
And finally, none of the evidence pointed to by creationists actually proves their case; instead, their evidence is usually the product of either scientific incompetency or just a general ignorance of how to properly use these techniques. These dating methods will continue to provide accurate results going forward while creationists will continue to embarrass themselves by maintaining that the Earth is 6, years old in the face of all the evidence.
The decay rate is measured in terms of the half-life of the element, or the time it takes for half of the element to split into its daughter atoms. The half-life of U is 4. When the mineral or glass is heated, the tracks are erased in much the same way cut marks fade away from hard candy that is heated.
This process sets the fission track clock to zero, and the number of tracks that then form are a measure of the amount of time that has passed since the heating event. Scientists are able to count the tracks in the sample with the aid of a powerful microscope.
The sample must contain enough U to create enough tracks to be counted, but not contain too much of the isotope, or there will be a jumble of tracks that cannot be distinguished for counting.
One of the advantages of fission track dating is that it has an enormous dating range. Objects heated only a few decades ago may be dated if they contain relatively high levels of U; conversely, some meteorites have been dated to over a billion years old with this method. See also Pollen analysis ; Strata. Dickin, Alan P. Radiogenic Isotope Geology. Balter, Michael. Guilderson, Tom P. Turney, Chris S. Cite this article Pick a style below, and copy the text for your bibliography.
July 10, Retrieved July 10, from Encyclopedia. Then, copy and paste the text into your bibliography or works cited list. Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia. Dating techniques are procedures used by scientists to determine the age of a specimen.
Relative dating methods tell only if one sample is older or younger than another sample; absolute dating methods provide a date in years.
Many absolute dating techniques take advantage of radioactive decaywhereby a radioactive form of an element is converted into another radioactive isotope or non-radioactive product at a regular rate. In recent years, a few of these methods have undergone continual refinement as scientists strive to develop the most accurate dating techniques possible.
It is based on the assumption which, except at unconformitiesnearly always holds true that deeper layers were deposited earlier, and thus are older than more shallow layers.
Although these units may be sequential, they are not necessarily continuous due to erosional removal of some intervening units. The technique works best if the animals belonged to species that evolved quickly, expanded rapidly over a large area, or suffered a mass extinction.
This process results in a "rain" of pollen that falls over many types of environments.
In most cases, this also reveals much about the climate of the period, because most plants only thrive in specific climatic conditions.
This dating technique of amino acid racimization was first conducted by Hare and Mitterer inand was popular in the s. Amino acid racimization is based on the principle that amino acids except glycine, a very simple amino acid exist in two mirror image forms called stereoisomers. This may form a D-amino acid instead of an L - amino acid. The rate at which the reaction occurs is different for each amino acid; in addition, it depends upon the moisture, temperatureand pH of the postmortem conditions.
It can be used to obtain dates that would be unobtainable by more conventional methods such as radiocarbon dating. Although cation-ratio dating has been widely used, recent studies suggest it has potential errors. Thermoluminescence dating is very useful for determining the age of pottery. This radiation may come from radioactive substances such as uranium. The longer the radiation exposure, the more electrons get bumped into an excited state.
With more electrons in an excited state, more light is emitted upon heating. Scientists can determine how many years have passed since a ceramic was fired by heating it in the laboratory and measuring how much light is given off. Optically stimulated luminescence OSL has only been used since It is very similar to thermoluminescence dating, both of which are considered "clock setting" techniques.
To determine the age of sediment, scientists expose grains to a known amount of light and compare these grains with the unknown sediment. A disadvantage to this technique is that in order to get accurate results, the sediment to be tested cannot be exposed to light which would reset the "clock"making sampling difficult.
The absolute dating method utilizing tree ring growth is known as dendrochronology. Dendrochronology has a range of one to 10, years or more. As previously mentioned, radioactive decay refers to the process in which a radioactive form of an element is converted into a decay product at a regular rate.
Potassium-argon dating relies on the fact that when volcanic rocks are heated to extremely high temperatures, they release any argon gas trapped in them. Radiocarbon dating is used to date charcoal, wood, and other biological materials. The range of conventional radiocarbon dating is 30, - 40, years, but with sensitive instrumentation, this range can be extended to 70, years. Relative to their atmospheric proportions, atoms of 14 C and of a non-radioactive form of carbon, 12 C, are equally likely to be incorporated into living organisms.
This allows them to determine how much 14 C has formed since the death of the organism. One of the most familiar applications of radioactive dating is determining the age of fossilized remains, such as dinosaur bones.
This method is known as radiometric dating. Some commonly used dating methods are summarized in Table 1. The rate of decay for many radioactive isotopes has . 14 Carbon Dating. Radiocarbon dating is different than the other methods of dating because it cannot be used to directly date rocks, but can only be used to date organic material produced by once living organisms. 14 C is continually being produced in the Earth's upper . Dating methods fall into four basic categories (Figure ): (a) radioisotopic methods, which are based on the rate of atomic disintegration in a sample or its surrounding environment; (b) paleomagnetic (correlation) methods, 1 which rely on past reversals of the Earth's magnetic field and their effects on a sample; (c) organic and inorganic chemical methods, which are based on time.
Radioactive dating is also used to authenticate the age of rare archaeological artifacts. Because items such as paper documents and cotton garments are produced from plants, they can be dated using radiocarbon dating.
It's funny to watch creationists point out the variance of certain decay rates-as if they're the first ones to figure this out or something, as if the experts in the field who use these dating methods have never considered the possibility of variance or other sources of inaccuracy, and when the creationist points out this possibility, the. Decay routes. Uranium decays to lead via a series of alpha (and beta) decays, in which U with daughter nuclides undergo total eight alpha and six beta decays whereas U with daughters only experience seven alpha and four beta decays. The existence of two 'parallel' uranium-lead decay routes ( U to Pb and U to Pb) leads to multiple dating techniques within the overall U. Radioactive decay dating is not a single method of absolute dating but instead a group of related methods for absolute dating of samples. Potassium-argon dating relies on the fact that when volcanic rocks are heated to extremely high temperatures, they release any argon gas trapped in them.
Without radioactive datinga clever forgery might be indistinguishable from a real artifact. There are some limitations, however, to the use of this technique.
Samples that were heated or irradiated at some time may yield by radioactive dating an age less than the true age of the object. Because of this limitation, other dating techniques are often used along with radioactive dating to ensure accuracy. Uranium series dating techniques rely on the fact that radioactive uranium and thorium isotopes decay into a series of unstable, radioactive "daughter" isotopes; this process continues until a stable non-radioactive lead isotope is formed.
The "parent" isotopes have half-lives of several billion years. Uranium series have been used to date uranium-rich rocks, deep-sea sediments, shells, bones, and teeth, and to calculate the ages of ancient lakebeds. In the case of daughter excess, a larger amount of the daughter is initially deposited than the parent.
Some volcanic minerals and glasses, such as obsidiancontain uranium U. Over time, these substances become "scratched. When an atom of U splits, two "daughter" atoms rocket away from each other, leaving in their wake tracks in the material in which they are embedded. Although certain dating techniques are accurate only within certain age ranges, whenever possible, scientists attempt to use multiple methods to date specimens.
Correlation of dates via different dating methods provides a highest degree of confidence in dating. See also Evolution, evidence of; Fossil record; Fossils and fossilization; Geologic time; Historical geology. Relative dating methods tell only if one sample is older or younger than another; absolute dating methods provide a date in years. Many absolute dating techniques take advantage of radioactive decaywhereby a radioactive form of an element is converted into a non-radioactive product at a regular rate.
The technique works best if the animals belonged to species which evolved quickly, expanded rapidly over a large area, or suffered a mass extinction. Pollen that ends up in lake beds or peat bogs is the most likely to be preserved, but pollen may also become fossilized in arid conditions if the soil is acidic or cool.
Decay rate dating methods
The varnish contains cations, which are positivelycharged atoms or molecules. This radiation may come from radioactive substances such as uraniumpresent in the clay or burial medium, or from cosmic radiation.
Thermoluminescence dating has the advantage of covering the time interval between radiocarbon and potassium-argon datingor 40,- years. As the rocks cool, argon 40Ar begins to accumulate.
Argon is formed in the rocks by the radioactive decay of potassium 40K. The amount of 40Ar formed is proportional to the decay rate half-life of 40K, which is 1. The reason such old material is required is that it takes a very long time to accumulate enough 40Ar to be measured accurately.
The range of conventional radiocarbon dating is 30, years, but with sensitive instrumentation this range can be extended to 70, years. Radiocarbon 14C is a radioactive form of the element carbon. It decays spontaneously into nitrogen 14N. Atoms of 14C and of a non-radioactive form of carbon, 12C, are equally likely to be incorporated into living organisms-there is no discrimination. The ratio will then begin to change as the 14C in the dead organism decays into 14N. This is the time required for half of the 14C to decay into 14N.
The half-life of 14C is 5, years. This allows us to determine how much 14C has formed since the death of the organism. The "parent" isotopes have half-lives of several thousand million years. Geyh, Mebus A. Absolute Age Determination. New York : Springer-Verlag, Oberhofer, and D. Regulla, eds. Scientific Dating Methods.
Boston: Kluwer Academic Publishers, Lewis, C. Fission-Track Dating. Movies and television have presented a romantic vision of archaeology as adventure in far-away and exotic locations.
A more realistic picture might show researchers digging in smelly mud for hours under the hot sun while battling relentless mosquitoes. This type of archaeological research produces hundreds of small plastic bags containing pottery shards, animal bones, bits of worked stone, and other fragments. These findings must be classified, which requires more hours of tedious work in a stuffy tent.
At its best, archaeology involves a studious examination of the past with the goal of learning important information about the culture and customs of ancient or not so ancient peoples. Much archaeology in the early twenty-first century investigates the recent past, a sub-branch called "historical archaeology. Archaeology is the study of the material remains of past human cultures.
It is distinguished from other forms of inquiry by its method of study, excavation. Most archaeologists call this "digging. That sort of unscientific digging destroys the archaeological information. Archaeological excavation requires the removal of material layer by layer to expose artifacts in place. The removed material is carefully sifted to find small artifactstiny animal bones, and other remains. Archaeologists even examine the soil in various layers for microscopic material, such as pollen.
Excavations, in combination with surveys, may yield maps of a ruin or collections of artifacts. Time is important to archaeologists. There is rarely enough time to complete the work, but of even greater interest is the time that has passed since the artifact was created.
An important part of archaeology is the examination of how cultures change over time. It is therefore essential that the archaeologist is able to establish the age of the artifacts or other material remains and arrange them in a chronological sequence. The archaeologist must be able to distinguish between objects that were made at the same time and objects that were made at different times.
When objects that were made at different times are excavated, the archaeologist must be able to arrange them in a sequence from the oldest to the most recent. Before scientific dating techniques such as dendrochronology and radiocarbon dating were introduced to archaeology, the discipline was dominated by extensive discussions of the chronological sequence of events.
Most of those questions have now been settled and archaeologists have moved on to other issues.
Remarkable, valuable decay rate dating methods think
Scientific dating techniques have had a huge impact on archaeology. Archaeologists use many different techniques to determine the age of an object. Usually, several different techniques are applied to the same object.
Relative dating arranges artifacts in a chronological sequence from oldest to most recent without reference to the actual date. For example, by studying the decorations used on pottery, the types of materials used in the pottery, and the types and shapes of pots, it is often possible to arrange them into a sequence without knowing the actual date.
In absolute datingthe age of an object is determined by some chemical or physical process without reference to a chronology. Relative Dating Methods. The most common and widely used relative dating technique is stratigraphy. The principle of superposition borrowed from geology states that higher layers must be deposited on top of lower layers.
Thus, higher layers are more recent than lower layers. This only applies to undisturbed deposits. Rodent burrows, root action, and human activity can mix layers in a process known as bioturbation. However, the archaeologist can detect bioturbation and allow for its effects. Discrete layers of occupation can often be determined.
For example, Hisarlik, which is a hill in Turkeyis thought by some archaeologists to be the site of the ancient city of Troy. However, Hisarlik was occupied by many different cultures at various times both before and after the time of Troy, and each culture built on top of the ruins of the previous culture, often after violent conquest.
Consequently, the layers in this famous archaeological site represent many different cultures. An early excavator of Hisarlik, Heinrich Schleimann, inadvertently dug through the Troy layer into an earlier occupation and mistakenly assigned the gold artifacts he found there to Troy.
Other sites have been continuously occupied by the same culture for a long time and the different layers represent gradual changes. In both cases, stratigraphy will apply. A chronology based on stratigraphy often can be correlated to layers in other nearby sites. For example, a particular type or pattern of pottery may occur in only one layer in an excavation.
If the same pottery type is found in another excavation nearby, it is safe to assume that the layers are the same age. Archaeologists rarely make these determinations on the basis of a single example. Usually, a set of related artifacts is used to determine the age of a layer. Seriation simply means ordering. This technique was developed by the inventor of modern archaeology, Sir William Matthew Flinders Petrie. Seriation is based on the assumption that cultural characteristics change over time.
For example, consider how automobiles have changed in the last 50 years a relatively short time in archaeology. Automobile manufacturers frequently introduce new styles about every year, so archaeologists thousands of years from now will have no difficulty identifying the precise date of a layer if the layer contains automobile parts.
Cultural characteristics tend to show a particular pattern over time. The characteristic is introduced into the culture for example, using a certain type of projectile point for hunting or wearing low-riding jeansbecomes progressively more popular, then gradually wanes in popularity. The method of seriation uses this distinctive pattern to arrange archaeological materials into a sequence.
However, seriation only works when variations in a cultural characteristic are due to rapid and significant change over time. It also works best when a characteristic is widely shared among many different members of a group. Even then, it can only be applied to a small geographic area, because there is also geographic variation in cultural characteristics. For example, 50 years ago American automobiles changed every year while the Volkswagen Beetle hardly changed at all from year to year.
Cross dating is also based on stratigraphy. It uses the principle that different archaeological sites will show a similar collection of artifacts in layers of the same age. Sir Flinders Petrie used this method to establish the time sequence of artifacts in Egyptian cemeteries by identifying which burials contained Greek pottery vessels.
These same Greek pottery styles could be associated with monuments in Greece whose construction dates were fairly well known. Since absolute dating techniques have become common, the use of cross dating has decreased significantly. Pollen grains also appear in archaeological layers. They are abundant and they survive very well in archaeological contexts. As climates change over time, the plants that grow in a region change as well.
People who examine pollen grains the study of which is known as pollen analysis can usually determine the genusand often the exact species producing a certain pollen type. Archaeologists can then use this information to determine the relative ages of some sites and layers within sites.
However, climates do not change rapidly, so this type of analysis is best for archaeological sites dating back to the last ice age. Absolute Dating Methods. Absolute dating methods produce an actual date, usually accurate to within a few years.
This date is established independent of stratigraphy and chronology. If a date for a certain layer in an excavation can be established using an absolute dating method, other artifacts in the same layer can safely be assigned the same age. Dendrochronology, also known as tree-ring dating, is the earliest form of absolute dating. This method was first developed by the American astronomer Andrew Ellicott Douglas at the University of Arizona in the early s. Douglas was trying to develop a correlation between climate variations and sunspot activitybut archaeologists quickly recognized its usefulness as a dating tool.
The technique was first applied in the American Southwest and later extended to other parts of the world. Tree-ring dating is relatively simple. Trees add a new layer of cambium the layer right under the bark every year. The thickness of the layer depends on local weather and climate. In years with plenty of rain, the layer will be thick and healthy.