Talk:Radiometric dating
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[edit] Sr -- Sm
The list of radiometric dating technics at the end of the article includes
- samarium-neodymium (Sr/Nd)
- samarium-yttrium (Sr/Y)
Both items begin with samarium (Sm), but the chemical symbol shown is that of strontium (Sr) instead of samarium. I'd fix it, but I don't know what was intended. Mike Sarles
- Fixed that (one was a duplicate) and removed the following for clarification and/or verification:
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- strontium-neodymium-hafnium-lead (Sr-Nd-Hf-Pb)
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- if it's real it can be put back. Vsmith 18:25, 27 August 2006 (UTC)
- These are ratios used in isotope dating of mantle plumes: "Popular with plume enthusiasts is the ratio of helium-3 to helium-4. A higher ratio is characteristic of deep mantle origin, they argue. Similar information can be gleaned from isotopes of the elements neodymium, strontium, lead, and hafnium. The ratio of 3He/4He increases over time as 4He is produced by the decay of uranium and thorium. The present day atmospheric 3He/4He ratio is 1.39x10-6, and is referred to as RA. Geochemists infer deep origins whenever 3He/4He are in excess of 9 to 10 RA. These ratios have been found at hot spot locations such as Hawaii, and are consistently different than the basalts of the mid-ocean ridges....A better interpretation would be that the high 3He/4He ratio arises from a deficiency in 4He in the upper mantle caused by low U+Th areas, and thus low rate of addition of radiogenic 4He." http://www.emporia.edu/earthsci/student/sedlacek2/mantle.htm It's also referred to in the book "Radioactive and Stable Isotope Geology" by Hans-Gunter Attendorn and Robert N.C. Bowen. Valich 00:18, 12 February 2007 (UTC)
[edit] "Radiometric" dating?
The section "Short-range dating techniques" in this article contain interesting descriptions concerning various dating methods such as dendrochronology, "varve analysis", "hydration dating" or "obsidian dating", and thermoluminescence.
Strictly speaking, however, those methods do not belong to the topic of Radiometric dating, the current title of this article. Therefore, in my opinion, one of three things should be done: (1) rewrite the section so as not to appear as overtly off-topic; (2) move those other techniques to their proper places and place a link in "See also" section; or (3) rename the article to reflect a more general topic such as "Dating techniques" or the like. What do others think about this? --HYC 21:32, 8 September 2006 (UTC)
- Moved three paragraphs to Incremental dating, which was a stub needing more info. Vsmith 22:17, 8 September 2006 (UTC)
Sorry. My fault. I thought U/U, Sr/Nd, Sr-Nd-Pb were radiometric datings but on further research I see they are isotope ratios. Valich 21:15, 10 September 2006 (UTC)
[edit] Illogical?
Couldn't this method of dating be disproved by observing the fact that when the sample was created, we don't know how much of the daughter isotope was already present? --DylJSmith 03:09, 9 January 2007 (UTC)
hahahaha. this stinks of YECism. we do know how much of the daughter isotope was already present - usually none. e.g. Zircon, Monazite will crystallise with uranium occasionally replacing zirconium in its lattice since both have the same charge and ionic size. Lead will not fit. therefore there is no lead initially present in zircon or monazite and whatever else contains Zr and U. the situation is similar for other minerals and radioisotopes. that was in my first ever fucking lecture on the subject, its not that hard to grasp.
someone needs to explain how it is actually pysically done - including stuff like this that is also relevant to mineralogy. i can't be arsed Ezkerraldean 13:26, 27 January 2007 (UTC)
[edit] Re: illogical: Supervening influences on half life of samples
I understand that the half-life of a radio-isotope is unaffected by temerature, pressure, etc. But don't other radiological sources have an effect? e.g. the atomic fallout from a meteorite or a supernova in a nearby star system. It seems such events could trigger substantial 'non-spontaneous' decay that would cause is discontinuity in the typical half-life curve and set dates off by an order of magnitude. Also the level of C-14 in the atmosphere could increase significantly in response to such events too: making a sample appear younger than it really is.
No? Are there any reliable sources research on this? Shortopinions 20:00, 29 March 2007 (UTC)
- Go to talk/radiocarbon dating, make a "history" and read last week's comments. Jclerman 21:00, 29 March 2007 (UTC)
