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- 1 Additional Methods
- 2 Archeological emphasis
- 3 Copyvio
- 4 Added longer introduction and definition, edited formatting, added some text on carbon-14 dating
- 5 Please give references for the following statements
- 6 Most precise dating method?
- 7 Article improvements
- 8 Would a world-wide natural disaster effect radioactive decay?
- 9 proposed addition to Potassium Argon section
- 10 Geology
I cleared up some things in the overall definition. It seemed to focus more on relative dating than absolute dating. There are several more absolute techniques available, I'll add them in when I have the time to pull out my text book from Principles of Archaeology. Sheora 08:59, 28 January 2007 (UTC)
I'm surprised that this article on absolute dating refers only to the field of archeology, as if geologists don't have much use for absolute ages of objects, materials, and events! I don't have time to edit right now, so if anyone finds this before I get back here, feel free to broaden the focus of this article to all of earth science, as well as archeology. -- BlueCanoe 23:36, 21 February 2006 (UTC)
I'm not sure if this holds true to the field of history elsewhere, but where I'm from the terms absolute and relative dating also applies to the dating of historic events. 188.8.131.52 04:46, 19 November 2006 (UTC)
Added longer introduction and definition, edited formatting, added some text on carbon-14 dating
This is the first thing I have edited, so I apologize if I have forgotten to do something properly.
I added a longer introduction, some alternative terms, and a bit of a discussion about radiocarbon dating. There is a great deal more that can be said about absolute dating, but I am afraid that I don't know that much about other techniques off the top of my head. I just saw this one while surfing around and thought that I should add a little something. Mander 19:25, 20 December 2005 (UTC)
Please give references for the following statements
This is also true of the heartwood of a tree, which will appear younger than the outer rings of the same tree because it has had less time to incorporate carbon-14 into its makeup.
...plants take in carbon–14 as they absorb carbon dioxide.
people use them as firewood, after which they become part of the archaeological record.
Jclerman 21:01, 11 July 2006 (UTC)
Most precise dating method?
What is the most precise dating method availible today? I heard carbon dating is only good for things 60,000 years old. If there are other methods which are used for older objects, does this insinuate that carbon dating is more precise for newer objects? Inforazer 20:38, 19 September 2006 (UTC)
This entry would be greatly improved by including tree ring dating (bristlecone pine and European oaks) and Greenland ice core dating (esp. GRIP and GISP cores from Summit Camp) which provide accurate absolute dates for the most recent 8,000 years or more and are used extensively in climatological studies. Phaedrus7 (talk) 02:10, 6 February 2008 (UTC)
Expanding on the comments above, this article, although dealing with scientific processes doesn't handle this difficult subject well, making quite a few subjective, vague comments. Statements such as "Because the half-life of carbon-14 is short, the older a specimen is the greater the margin or error becomes." are incorrect, or at least non-sequiturs or ineptly explained. Another example is "Radiation levels do not remain constant over time." If one already understands the concept, this is comprehensible, but for someone who does not, it omits crucial information, e.g., how drastically and how frequently this factor comes into play. Statments like "has been very useful in this regard" don't convey much information. Useful how? When? As opposed to what? Most troubling, the article doesn't provide a framework to understand the larger, more difficult problems with absolute dating, i.e., how combinations of dating are chosen and how they affect accuracy.
This subject is too complicated to be dealt with piecemeal. I suggest someone take it on themselves to rewrite the whole thing, incorporating, however much of the existing material.
Would a world-wide natural disaster effect radioactive decay?
Historical documents can help verify the absolute date of an object, but beyond the beginning of recorded history, how can we verify the accuracy of our radioactive decay-based dating process? Perhaps some world-wide disaster created an abundance of radioactive decay. —Preceding unsigned comment added by 184.108.40.206 (talk) 01:31, 15 April 2008 (UTC)
proposed addition to Potassium Argon section
In order to do Potassium/Argon dating (In fact, all isochron dating methods) there are some assumptions that must be accepted as true. The following list of assumptions comes from McDougall I. and Harrison, T.M. (1988)
"As with all isotopic dating methods, there are a number of assumptions that must be fulfilled for a K-Ar age to relate to events in the geological history of the region being studied. These same assumptions also apply to the 40Ar/39Ar method, although this latter technique provides greatly increased opportunities for their testing. The principal assumptions are given below with brief comment as to their validity, and will be further discussed implicitly or explicitly in the following chapters."
1. "The parent nuclide, 40K, decays at a rate independent of its physical state and is not affected by differences in pressure or temperature. This is a major assumption, common to all dating methods based on radioactive decay; the available evidence suggest that it is well founded (Friedlander et al., 1981). Although changes in the electron capture partial decay constant for 40K possibly may occur at high pressures, theoretical calculations by Bukowinski (1979) indicate that for pressures experienced within a body of the size of the Earth the effects are negligibly small."
2. "The 40K/K ratio in nature is constant. As 40K is rarely determined directly when ages are measured, this is an important underlying assumption. Isotopic measurements of potassium in terrestrial and extraterrestrial samples indicate that this assumption is valid, at least to the extent that no differences greater than about 3% have been reported in the 39K/41K ratio. The evidence for the essentially constant isotopic ratios for the potassium isotopes will be presented in more detail subsequently."
3. "The radiogenic argon measured in a sample was produced by in situ decay of 40K in the interval since the rock crystallized or was recrystallized. Violations of this assumption are not uncommon. Well-known examples of incorporation of extraneous 40Ar include chilled glassy deep-sea basalts that have not completely outgassed preexisting 40Ar*, and the physical contamination of a magma by inclusion of older xenolitic material. Further examples will be discussed later, as the 40Ar/39Ar method allows the presence of extraneous argon to be recognized in some cases."
4. "Corrections can be made for nonradiogenic 40Ar present in the rock being dated. For terrestrial rocks the assumption generally is made that all such argon is atmospheric in composition with 40Ar/36Ar = 295.5, and although this commonly is so, there are exceptions. Various ways of assessing this assumption are available including the use of isotope correlation diagrams. Extraterrestrial samples such as meteorites and lunar rocks have nonradiogenic argon of quite different composition to that of atmospheric argon, but corrections often can be made satisfactorily, particularly as the nonradiogenic contributions usually are minor."
5. "The sample must have remained a closed system since the event being dated. Thus, there should have been no loss or gain of potassium or 40Ar*, other than by radioactive decay of 40K. Departures from this assumption are quite common, particularly in areas of complex geological history, but such departures can provide useful information that is of value in elucidating thermal histories. "
"These basic assumptions must be tested and assessed in each study that is undertaken. This is usually best done by measuring a suite of rocks or minerals from the area under study. The consistency or lack of consistency of the results, together with knowledge of the geology of the area, allows assessment of some of these assumptions, and provides the basis for conclusions as to the reliability and meaning of the measured ages. As will become evident later, an important advantage of the 40Ar/39Ar dating method is that the assumptions underlying calculation and interpretation of an age are more readily assessed than is the case for conventional K-Ar age measurements."
McDougall I. and Harrison, T.M., 1988, "Geochronology and Thermochronology by the 40Ar/39Ar Method", Oxford Monographs on Geology and Geophysics No. 9., pp. 11, 12. This book explains the ins and outs of the 40Ar/39Ar method of geochronology written by those intimately involved in its development.
All of these assumptions must be true for the method to be valid. The Boolean expression shows the relationship of the truth of the assumptions to the validity of the Isotopic Dating method.
(Asm. 1: TRUE) AND (Asm. 2: TRUE) AND (Asm. 3: TRUE) AND ( Asm. 4: TRUE) AND (Asm. 5: TRUE) = (Method: TRUE)
- Now that they have been added to the Potassium-argon dating page, no reason to add them here. Mikenorton (talk) 15:54, 21 July 2008 (UTC)
Absolute dating as a concept isn't limited to archaeology; it's also very important in geology, and I don't think that the article reflects that. I may get to this eventually, but it's not #1 on my to-do list right now, so I thought I'd drop a note/hint. Awickert (talk) 01:57, 15 March 2009 (UTC)