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by Max Power on April 3rd, 2005

Max Power

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How reliable are all the different dating methods?

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  • by geobill on March 17th, 2006

    geobill

    Owen Davis at U of Arizona has a nice set of web pages discussing various dating and paleo-environmental methods associated with his palynology (pollen analysis) class at http://www.geo.arizona.edu/palynology/geos462/. A brief summary follows:
    Radiocarbon is still the standard between 1950 and about 50,000 years ago. See http://www.geo.arizona.edu/palynology/geos462/10radiometric.html. Although decay counts (conventional radiocarbon dating) are still used, the most precise measurements are generated by Atomic Mass Spectroscopy (AMS ages). AMS ages are <b>precise</b> within better than 1%. However, because they are based on the absorption of atmospheric 14C by organisms, because atmospheric 14C is formed from 14N by energetic radiation, and because the radiation flux varies with the strength of the Earth's magnetic field, the <b>accuracy</b> of radiocarbon ages varies with time. The radiocarbon technique has been calibrated by dating individual tree rings, themselves accurate to within a few years, and by comparing shell and coral dates by both 14C and U/Th ages. Some 14C measurements yield unique ages but others can reflect a range of ages.

    Several other dating methods are commonly used in archeology including obsidian hydration rind dating and luminescence dating. The former uses the semi-predictable addition of water to the edges of worked obsidian flakes and the latter uses the accumulation of excited electrons in the structures of quartz or feldspar over time. And, of course, if an artifact can be dated at one place the numerical age is often carried elsewhere by correlation when artifacts of a similar style are found.

    Finally, although the age may be precise and accurate, the interpretation may be flawed. I heard of a colleague who tried to date the last glaciation by dating a tree trunk in glacial till (a technique that has yielded good data elsewhere). The date came back modern (contaminated with bomb carbon.). The material was till, but the tree had apparently been incorporated in it by a recent landside!

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  • by Joshua Zambrano on March 6th, 2006

    Joshua Zambrano

    Many of the dating methods rely on variables like carbon remaining constant, even as geologic calamities are believed to have occurred (meteor showers wiping out the dinosaurs, ice ages, floods, etc...).

    Is it possible a huge amount of ice or water would change carbon levels drastically? If everything was under water as per the Biblical view, it seems quite plausible. The top of Mt. Everest is largely composed of sea shells and sea fossils, for example.

    Carbon 14 dating and other types have been found wrong, particularly in volcanic events where the event could be witnessed. Now some might say the lava could be older or something like that and throw it off. It does seem the dating types are not as reliable as they have been generally touted.

    To my knowledge, carbon dating and potassium argon are being less mentioned, and even carbon-14 dating is being less mentioned as it is being more heavily criticized like the other 2 methods. When I used to debate about this stuff, it reached the point where they gave up trying to back carbon-14 dating in light of new evidence and turned to dendrochronology, or tree ring dating, the reliability of which I'm not that sure of.

    At any rate, there's evidence for and against such methods, I mostly just mentioned some other factors that could affect their reliability.

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  • by Thom64 on April 6th, 2005

    Thom64

    Here you will get differing opinions. The fact is that it is impossible to verify very old dates. Some researchers have almost unlimited, unquestioned confidence in radiometric dating methods. Others have doubts. There are several unprovable (but reasonable) assumptions necessary to use radiometric dating. We can not prove the assumptions are valid in particular or general cases. Some swear by their dating methods while others swear at them (as it were...).

    I have read in one source of a forest encased in an ancient lava flow. We know a tree encased in stone stopped exchanging carbon with the atmosphere on the same day the rock around it was formed, but the rock and tree show dramatically different ages using generally accepted radiometric dating methods. In another case, an ancient animal was found frozen in a glacier and radiometric dating of different parts of the animal gave significantly different ages. These particular examples may have been explained since, but examples like these exist and give some skeptics enough reason not to rely on radiometric methods without confirmation.

    The "best" dating method probably uses multiple independent indicators. For example, if we have writings of a historian who witnessed a volcano eruption covering a city in a certain place at about the time of Julius Caesar and artifacts are found on the site consistent with the time of Julius Caesar we can be quite confident about the date of the volcanic event. Without the written record, the possibility exists that the volcano covered a house with a collection of old stuff sometime later.

    There are cases when art/technology, radiometric and written evidences are in conflict. In these cases the researcher has to formulate a best guess balancing his confidence in the paradoxical data.

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