Radiometric Dating Question (please debunk)

[Netheralian]

In discussion with the usual offenders - his quote:

The 11 Grand Canyon rock samples :

Dating Method:
Potassium-Argon

Millions of years:
841.5

Type of data (whole rock or separate mineral within the rock):
11 Whole rock samples

--------------------------------------------
Dating Method:
Lead-Lead (isochron)

Millions of years:
1,250

Type of data (whole rock or separate mineral within the rock):
11 Whole rock samples
---------------------------------------------

Source:
.A. Snelling, S.A. Austin, and W.A. Hoesch, Radioisotopes in the diabase sill (Upper Precambrian) at Bass Rapids, Grand Canyon, Arizona: an application and test of the isochron dating methods, in R.L. Ivey, Jr. (Ed.), Proceedings of the Fifth International Conference on Creationism, Creation Science Fellowship, Pittsburgh, Pennsylvania, pp. 269-284, 203.
S.A. Austin, in Vardiman et al., 2005, 325-392.
D. DeYoung, 2005, 109-121.

Now before you say it doesn't count because these scientists work for the RATE team and are creationists, just look at the data. Instead of the standard for testing 4 samples, they tested 10 samples. They took each sample to a lab where all geologists, etc. go to get an age.

For starters he started implying a 3 order of magnitude but I see not a huge variation between the two samples (I mean it's 1 billion years +/- 20% - i don't actually think that its too bad). Can anyone point out and specific flaws? (Not too much conjecture - I want some hard facts. I.e. incorrect method and why (wrong rock type), high error based on the half life of Potassium-Argon or Uranium-Lead etc. Or is it valid and acceptable error based on the time scale involved?

Original article: http://www.icr.org/article/radioisotopes-diabase-grand-canyon-isochron-dating/

 

[Netheralian]

From the article linked:

It is therefore argued that only changing radioisotope decay rates in the past could account for these discordant isochron "ages" for the same geologic event.

I would argue as this being the "only" explanation of the variation of rates as outright absurd as they seem to have dismissed everything else out of hand... Once again, someone with more experience on the topic appreciated.

 

[orpiment99]

I'm not a petrologist or geochemist and therefore am a poor person to get an explanation from. However, here is an article that does address some of the what you're asking:

http://petrology.oxfordjournals.org/cgi/content/full/45/9/1747

 

[Squawk]

Ok, first problem to note is that I distrust the source. I cannot tell where they are lying, and I have good reason to suppose that they are.

That said, lets go with it.

First up, we find this

Cardenas basalt dated at 1090 +- 70Ma by RB-SR
Shianu Creek Sill 1070+-30Ma

And then the bollocks begins. I have only highlighted the important bit.

Although these dates are obviously identical...

Lets think about that, shall we.
The possible ranges for those dates do indeed cross. However, it is entirely possible, given the margin for error quoted, that the rocks sampled here are actually 120Ma out.
120 million years, identical ages. Hmm, by that logic humans could be said to live 60 million years BEFORE the dinosaurs went extinct.

Of key interest to me in that line is the use of "obviously", which is used to direct the reader to a bogus conclusion.

Onwards...

There is then a list of ages given for various samples, but I confess not to know anything about this particular location so I don't know what they are comparing. Actually neither do the authors, since they insert at "presumably" to cover themselves. The ages are all similar and all are cited from other papers, I have no reason to doubt them.

And then we find more duplicity.
A discrepancy was found between two samples, and the authors of the original papers offered up explanations. Actually they offered up two.

1. Different sources of magma, ie different times of deposition.
2. Crustal contamination.

Note that these discrepancies did NOT reveal a wrong age, but rather different starting concentrations of elements.

The author of the paper then sneaks in the creotard explanation. They offer three "alternative" options.
1. argon inheritance
2. argon mixing
3. Variable rates of radiometric decay.

Guess which one they are going to pitch for. As a slight diversion, anyone with a subscription might be intersted in http://bulletin.geoscienceworld.org/cgi/content/abstract/69/2/151

Sadly I don't have one, would like to read that. Alas, mebbe womble can get it?

It is impossible for me to offer an opinion on the ages they got back from dating the rocks. Given previous creationist dishonesty I am inclined to suggest that either they lied about the results or lied about the samples. The simply fact that I can find errors in the first part of the paper is enough for me to discount the latter half of it, someone with better knowledge than me will have to tackle the rest.

This is most of the reason why I trust peer review. A qualified team of experts would shoot through this shit in seconds, I can't since it is not my area. Still, I can show why this is bullshit in the first half, which suffices for me

 

[Womble]

Right, i'm a bit tired to be looking into this now when i have work tomorrow. I've dug out one of my textbooks and it looks like i've got something relavent in that. I'll check out the originl article and the one that someone else linked too. The one for 1958 has probably been superceeded by newer work so i wouldn't worry too much about that!

 

[scalyblue]

http://www.talkorigins.org/indexcc/CD/CD014_1.html

1. One of the requirements for isochron dating is that the samples be cogenetic, that is, that they come from materials that were isotopically homogeneous (with respect to each other) when they formed. Austin's selection of samples violated this assumption. His five samples came from four different lava flows plus one phenocryst (which likely solidified in the magma chamber before the flow). Thus, Austin's conclusion, not the isochron method, is invalid.

2. Noncogenetic samples such as Austin used are sometimes used intentionally to determine the age of the common source of the samples. Austin's results confirm that the lithospheric mantle underlying the Grand Canyon (the common source for his samples) is older than the Cardenas Basalt. Geologists have known this all along.

3. Austin (1988) cited Brooks et al. (1976), showing Austin should have been aware that noncogenetic samples could produce an isochron for the age of their molten material's source. His misstatement of the significance of the isochron is just plain sloppy.

 

[Squawk]

http://www.talkorigins.org/indexcc/CD/CD014_1.html

1. One of the requirements for isochron dating is that the samples be cogenetic, that is, that they come from materials that were isotopically homogeneous (with respect to each other) when they formed. Austin's selection of samples violated this assumption. His five samples came from four different lava flows plus one phenocryst (which likely solidified in the magma chamber before the flow). Thus, Austin's conclusion, not the isochron method, is invalid.

2. Noncogenetic samples such as Austin used are sometimes used intentionally to determine the age of the common source of the samples. Austin's results confirm that the lithospheric mantle underlying the Grand Canyon (the common source for his samples) is older than the Cardenas Basalt. Geologists have known this all along.

3. Austin (1988) cited Brooks et al. (1976), showing Austin should have been aware that noncogenetic samples could produce an isochron for the age of their molten material's source. His misstatement of the significance of the isochron is just plain sloppy.

yay, I guessed right

Thanks for posting that, should really have checked talkorigins

 

[Netheralian]

Shit - I normally check talkorigins first but for some reason I decided that this may be a little too specific for them to have picked up.

Thanks All for the input

 

[scalyblue]

Talkorigins is the batman of debunking dumb arguments ^.^

 

[Geochron]

There remains a possibility that some or all of the samples have been significantly reworked and may have inherited radioisotopic signatures from older rock. This has been well studied w/ the Acasta Gneiss (oldest rocks on Earth) and comparative samples taken from Hudson Bay that dated about 8% older.

 

[orpiment99]

As a slight diversion, anyone with a subscription might be intersted in http://bulletin.geoscienceworld.org/cgi/content/abstract/69/2/151

Sadly I don't have one, would like to read that.

I have a pdf file of it. If you'd like it, p.m. me.

As to the article itself, it is from 1958. I haven't had time to finish reading it yet, but I have started. To my knowledge, K-Argon has never been extensively used in dating sed rocks. Presumably, it is too expensive when biostratigraphy can give us dates that are as accurate as any that can be produced with radiometric dating on sed rocks. Honestly, I would personally have trouble trusting the dates given from any radiometric dating on a sedimentary rock.

 

[Squawk]

As a slight diversion, anyone with a subscription might be intersted in http://bulletin.geoscienceworld.org/cgi/content/abstract/69/2/151

Sadly I don't have one, would like to read that.

I have a pdf file of it. If you'd like it, p.m. me.

As to the article itself, it is from 1958. I haven't had time to finish reading it yet, but I have started. To my knowledge, K-Argon has never been extensively used in dating sed rocks. Presumably, it is too expensive when biostratigraphy can give us dates that are as accurate as any that can be produced with radiometric dating on sed rocks. Honestly, I would personally have trouble trusting the dates given from any radiometric dating on a sedimentary rock.

I agree with you on the dating of sedimentary rocks, useful for dating the content but not for dating the formation of the formation itself. The reason I was interested in that article was simply as an example of the sound alternatives they offered and how they have been known for so long, the processes now well understood.

 

[Womble]

Radiometric dating is used to date sed rocks???

Whilst not a sedimentologist i'm open to correction, but you can't date sed rocks this way. You can date any included igneous or metamorphic material but not material based on detrital sediments.

 

[orpiment99]

Radiometric dating is used to date sed rocks???

Whilst not a sedimentologist i'm open to correction, but you can't date sed rocks this way. You can date any included igneous or metamorphic material but not material based on detrital sediments.

Agreed. When I searched for similar articles everything came back from the 50's. I think it was a short lived idea.

As I stated before, I haven't read it all yet, but they were discussing the usefulness of certain K bearing minerals. There was also some discussion on weathering into clay.

However, here is the paper under discussion (Squawk posted a link if you have a subscription):

Curtis, G.H. and J. H. Reynolds. Notes on the Potassium-Argon Dating of Sedimentary Rocks. Bulletin of the Geological Society of America v. 69 p. 151-160 1958

 

[Womble]

Yeah, i know it's linked in above. I've not sat down to read it yet.

 

[Deleted member 499]

Radiometric dating is used to date sed rocks???

Whilst not a sedimentologist i'm open to correction, but you can't date sed rocks this way. You can date any included igneous or metamorphic material but not material based on detrital sediments.

The best that you can generally do with radiometric dating in sedimentary rocks is to establish an upper limit. If you date igneous or metamorphic components then you can establish the age of the source rock (or at least part of it) but you'll never get the date of formation of the sedimentary rock itself. It's quite useful if you're dating rocks which don't really have any fossil content like the Torridonian sandstones in Scotland.

As far as K-Ar dating goes. I was always under the impression that it's not a particularly good method as the daughter product is gaseous and thus prone to leakage and therefore easy to reset as well which would explain why the K-Ar dates were younger. My first thoughts to this would be to find out if there's been any metamorphic events in the area since the sill was emplaced which would have caused loss of daughter products.

 

[Womble]

Radiometric dating is used to date sed rocks???

Whilst not a sedimentologist i'm open to correction, but you can't date sed rocks this way. You can date any included igneous or metamorphic material but not material based on detrital sediments.

The best that you can generally do with radiometric dating in sedimentary rocks is to establish an upper limit. If you date igneous or metamorphic components then you can establish the age of the source rock (or at least part of it) but you'll never get the date of formation of the sedimentary rock itself. It's quite useful if you're dating rocks which don't really have any fossil content like the Torridonian sandstones in Scotland.

As far as K-Ar dating goes. I was always under the impression that it's not a particularly good method as the daughter product is gaseous and thus prone to leakage and therefore easy to reset as well which would explain why the K-Ar dates were younger. My first thoughts to this would be to find out if there's been any metamorphic events in the area since the sill was emplaced which would have caused loss of daughter products.

I know that you can never get the age of a sed rock by dating igneous or metamophic rocks but i was directing my comment at the idea of daiting sed rocks directly using radiometric methods.

i've not personally done any radiometric dating but i do agree that checking for metamorphic activity against a dating clock having been reset is always a good idea.