Two questions concerning Radioisotope dating

One thing I've always wondered about radioisotope dating is how does it work? I guess what I'm asking is, let's say you want to date a sediment layer. When you test it, why doesn't the date measure how old the particles that formed the sediment? Is something renewed when layers of sediment are formed?I don't know how to make my question any clearer, so let me give an anlogy. If I date a rock at 65 million years old, then I chop up the rock into itty bitty peices a 65 million years later and form a layer with them, then 65 million years later I date the layer. Will I get 195 million years? Or 65 million years?That should do it.My second question is something I've seen asked, but I never hear an answer to, and I'm wondering what the explanation is. I'm perfectly fine with "we don't have an explanation yet..." I just want to know if there is one!Why do different dating methods match each other?If I was going to speculate and try and answer my own questions...#1) New bonds form when rock comes together? It is those bonds that are measured?#2) If constants have changed, this is exactly what you would expect. If before the change, you date rocks at 1000 years old. After the change... 65 million years old. In other words, they *should* all agree?Just some un-scientific un-educated guessesThanks,David

David, I'll leave your first question to those who are better qualified and experienced in the matter of radiometric dating. However your second question appears to be based on the premise that radiometric dating is wrong when it gives results in the millions and billions of years when you have the preconception from your religious tenets that it can't be more than about 10,000 years old.A very readable article on radiometric dating can be found at Radiometric Dating It incidentally shows that you don't have to give up cristian beliefs to accept the accuracy of radiometric dating. When reading through you might notice that a range of isotopes can be used for dating purposes, including Samarium-147 (106 billion year half life), Uranium-238 (half life 4.5 billion years) and potassium-40 (half life 1.26 billion years). Yes, creationists have a very big problem explaining why such isotopes have undergone accelerated radioactive decay so that they all co-incidentally now give the same radiometric date when tested.And one of the posters here, Joe Meert, provides examples of consistent dating of the same rocks by a variety of isotopes at One of the main objections to radiometric dating Perhaps you might consider the obvious answer to your question "Why do different dating methods match each other?" - that they are accurately measuring the same thing - the real age of the rock.BTW, chemical bonds have nothing to do with the matter except to the extent that they allow the formation of crystals which contain the radioactive isotopes and also retain the daughter products after they are produced.

HalyconYour first question is a very good one. The key is that the routine dating done these days is dating of igneous rocks - formed from magma flows. After solidifying the decaying elements and their proucts are generally locked in. I guess the fact that they are magma means that the initial state of the rock is also reset due to liquificaiton and hence existing duaghter products will be mixed in to an average low concentration. A proffesional geologits might need to correct me on the later half. Dating of sedimentary rocks themselves will give the dates of the original rock as you correctly pointed out although Joe here I think tried to explain a mehtod to me for dating the actual deposition age (??)The second point about the match is a puzzle for creaitonists and we have wondered over the years whether geologists pick and chose their results and try to find good reasons to throw away 'bad' data but quickly accept 'good data'. While I don't doubt that some of this has been done most modern creaitonists have recently (the last 10 years) begun to accept that the decay has actually occurred. So we beleive that decay was accelreated - possibly to cause the flood via radiogenic heating of the crust and mantle. The 'RATE' goup of creationist geologists/physicists have pointed out data that backs this up. There is far too much helium in deep granites suggesting it (the product opf decay) hasn't had time to diffuse out yet. that puts the decay as millions of years worth - but recently! Peple here debate the validity of this helium retention work claiming tha tthe zircon particles are able to hold the helium in for millions of years. We'll have to see how this turns out.It is also certianly true that there are numerous examples of recent lava flows that have returned ridiculously old ages. But to deny that there is more decay in deeper rocks or that the decays haven't occurred is simply incorrect. I personally side with the 'RATE' group - God must have accerlsatd decay - and probably for a good reason - to tectonically start of the flood.

Radiometric dating of sedimentary rocks can be done in a variety of ways. Indirectly, the reversal stratigraphy of the sequence can be determined (similar to barcoding) and tied to a radiometrically dated time scale. Direct methods are improving specifically U-Pb dating of carbonates. We can also determine a range of ages on detrital zircons which will help us determine a maximum age of sedimentation. Volcanic ash layers between sedimentary units also provide a 'bracketing' of ages for sedimentary records. Despite TB's assertion, there is no evidence that decay rates were faster in the past. Rapid decay poses a serious heat problem which I outline here ROASTING ADAM-Creationism's Heat Problem . There is also negative evidence for rapid plate tectonics outlined here at THE DEPTHS OF THE OCEANS In short, the earth is old and there is NO evidence for a 6000-10000 year old earth.CheersJoe Meert

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Originally posted by Tranquility Base:
The second point about the match is a puzzle for creaitonists and we have wondered over the years whether geologists pick and chose their results and try to find good reasons to throw away 'bad' data but quickly accept 'good data'.

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Well, actually, some creationists have come out and stated this quite explicitly.

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...I personally side with the 'RATE' group - God must have accerlsatd decay - and probably for a good reason - to tectonically start of the flood.

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Must'a been! Of course you have to blindly accept that there was a biblical flood to even begin to divine such a mechanism. Because there is no evidentiary support whatever for accelerated decay. It is a construct that is NECESSARY to rationalize a belief in a flood.

So guys did I get that aspect right about the liquified state of magma causing the 'resetting'? Is it (i) that liquificaiton creates a uniform distribution of existing decay products at low average background or is it that liquificaiton seperates out the existing products away from the parent? I have always wondered this and never read about it in plain English (or if I did I've forgotten).

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Originally posted by Tranquility Base:
So guys did I get that aspect right about the liquified state of magma causing the 'resetting'?

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Well, first, it would actually be 'setting.' And second, the clock is actually set when the mineral in question goes below its specific trapping temperature, so the clock is actually set when the rock cools below a certain known temperature. That is why they are often called 'cooling dates' or 'uplift dates.' The rock is probably already solid.

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Is it (i) that liquificaiton creates a uniform distribution of existing decay products at low average background or is it that liquificaiton seperates out the existing products away from the parent?

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More the latter than the former. A homogeneous mixture would be easier to work with, but partitioning of some elements would make the dating more accurate. Argon, for instance is asssumed to not fit into the lattice of a microcline or biotite crystal, but appears to some how be accomodated into the pyroxene. That is why creationists prefer to do K-Ar dates on pyroxene. It is a known bad actor. Argon might also partition into aqueous or gaseous phases making less likely to enter minerals in the center of the pluton. Furthermore, since it is a noble gas it does not readily combine with anything. All these things make K-Ar one of the easier and more understandable systems to work with (despite what creationists say).

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I have always wondered this and never read about it in plain English (or if I did I've forgotten).

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Kudos for asking. It seems most creationsits don't do so. They already 'know.'

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Originally posted by Tranquility Base:
Halycon

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There is far too much helium in deep granites suggesting it (the product opf decay) hasn't had time to diffuse out yet. that puts the decay as millions of years worth - but recently! Peple here debate the validity of this helium retention work claiming tha tthe zircon particles are able to hold the helium in for millions of years. We'll have to see how this turns out.

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Out of curiosity, is there anything more substantial to back up the conclusion of excess retained helium? Creationists aren't still relying on Gentry's mixed results are they? Have measurements been taken from rocks with a demonstrably stable history without periods of magma intrusion or heating?

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Originally posted by wj:

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Originally posted by Tranquility Base:
Halycon

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There is far too much helium in deep granites suggesting it (the product opf decay) hasn't had time to diffuse out yet. that puts the decay as millions of years worth - but recently! Peple here debate the validity of this helium retention work claiming tha tthe zircon particles are able to hold the helium in for millions of years. We'll have to see how this turns out.

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Out of curiosity, is there anything more substantial to back up the conclusion of excess retained helium? Creationists aren't still relying on Gentry's mixed results are they? Have measurements been taken from rocks with a demonstrably stable history without periods of magma intrusion or heating?

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Gentry never went to a depth beyond the closure temperature of zircons for helium. Estimated diffusion temps for zircon are in the range 200-230 C, the deepest sample from Gentry's 'study' was from a dpeth with a temperature of 195 C. In essence, Gentry confirmed the closure temp for zircon was above 195 C. He was correct.CheersJoe Meert

[QUOTE]Originally posted by wj:
Originally posted by Tranquility Base:There is far too much helium in deep granites suggesting it (the product opf decay) hasn't had time to diffuse out yet. that puts the decay as millions of years worth - but recently! Peple here debate the validity of this helium retention work claiming tha tthe zircon particles are able to hold the helium in for millions of years. We'll have to see how this turns out.
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wj: Out of curiosity, is there anything more substantial to back up the conclusion of excess retained helium? Creationists aren't still relying on Gentry's mixed results are they? Have measurements been taken from rocks with a demonstrably stable history without periods of magma intrusion or heating?

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You'd think this one would be dead by now, but as long as it is hosted by creationist websites, we will be refuting it. I know that someone here has a very good refutation, but I (stupidly thinking the argument ended) never copied it. I'll try to check the records.

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Originally posted by Tranquility Base:

It is also certianly true that there are numerous examples of recent lava flows that have returned ridiculously old ages. But to deny that there is more decay in deeper rocks or that the decays haven't occurred is simply incorrect. I personally side with the 'RATE' group - God must have accerlsatd decay - and probably for a good reason - to tectonically start of the flood.

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I almost let this misrepresentation slip through. The majority of ridiculously old ages for recent lava flows come from creationists who choose to ignore best practice and avoid known problems. However accurate dates (given the margin of error for a method which is designed to date materials from hundreds of thousands to billions of years in age) can be obtained with care and expertise. Dalrymple notes on such success at
http://www.ncseweb.org/...ic_dating_does_work_12_30_1899.asp See Dating of the Mt Vesuvius Eruption.Other successful datings of recent lava flows are mentioned at
http://www.gate.net/~rwms/AgeEarth.html under Historical Volcanic Lavas Dated at Zero from K40/Ar40.TB, do you think that the rate group will put their methodology, results and conclusions to professional scrutiny or will they simply preach to the converted?

EdgeI think Wehappy has the best refutaiton of the helium retention work.

Thanks Edge - so dating relies on liquificaiton/crystallization partitioning the parent.

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Interesting... have the creationist heard and responded to this accusation? What do they say about the accurate dating of known lava flows?

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If it works on known ages... then we should be able to continue to date deeper and deeper layers, and at the points where radioisotope decay rate was higher should be obvious no?

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Known Layer - 2000
Next Layer - 3000
Next Layer - 50 million

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Am I right?

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By the way, anyone with the R.A.T.E's first 700 page book here? I'm wondering if someone with very little education in the area would be able to follow it.

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David

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Originally posted by halcyonwaters:
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Interesting... have the creationist heard and responded to this accusation? What do they say about the accurate dating of known lava flows?

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If it works on known ages... then we should be able to continue to date deeper and deeper layers, and at the points where radioisotope decay rate was higher should be obvious no?

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Known Layer - 2000
Next Layer - 3000
Next Layer - 50 million

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Am I right?

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David

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You'll have to ask the creationists how their model would works. It is my impression that they expect that the accelerated decay occurred at all levels in all isotopes so I don't think they would predict a discontinuity as you suggest above. In fact I don't recall creatinists ever giving a date for any rock sample which is less than 10,000 years old. All they manage to do is incorrectly apply the methods and come up with old dates for undoubtedly young rocks.