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Author Topic:   Radiometric Dating and the Geologic Column: A Critique
crashfrog
Member (Idle past 778 days)
Posts: 19762
From: Silver Spring, MD
Joined: 03-20-2003


Message 61 of 113 (166985)
12-10-2004 3:01 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
What evidence do you have that he's wrong?

This message is a reply to:
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Minnemooseus
Member
Posts: 3883
From: Duluth, Minnesota, U.S. (West end of Lake Superior)
Joined: 11-11-2001
Member Rating: 3.7


Message 62 of 113 (166990)
12-10-2004 3:15 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example (Calling JonF)
You seem to be getting into an example of rather great complexity here (welcome to the real world). My short response is, many different things can be discovered by studying such a system. One can get multiple legitimate dates from such things - They can date different events in the rocks history.

My bottom line is, the evolution side might be best served by letting one of our resident (real) experts respond to this, rather than the quasi-experts (such as myself) cluttering things up with our responses.

I think that means "Let's now hear from JonF".

Moose

Edited to add to subtitle.

This message has been edited by minnemooseus, 12-10-2004 03:16 PM


This message is a reply to:
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Joe T
Member (Idle past 1480 days)
Posts: 41
From: Virginia
Joined: 01-10-2002


Message 63 of 113 (166998)
12-10-2004 3:55 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
As is clearly seen, the geochronologist is sure to begin his experiment with rationalizations at hand, just in case.

I am sorry, but I do not clearly see this at all. I read your critique and the paper twice just to make sure. It seems to me that the only way one could come to the conclusions you did is to assign motives to the paper's authors that are not even hinted at in the paper itself. In other words it seems to me as if you approached this paper with the idea that geochronologists are skunks and picked out phrases from the paper to facilitate an amateur psychoanalysis in support of this thesis.

With all due respect,

Joe T.


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roxrkool
Member (Idle past 299 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 64 of 113 (166999)
12-10-2004 4:00 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
AC, having read your critical analysis of the paper, all I can say is that you do not fully understand the complexities of igneous systems, nor what results after having been affected by outside influences. However, you are probably the FIRST YEC I have ever seen to present such an analysis and I respect you greatly for it.

First, and anyone correct me if I am wrong (read the paper and wrote this post quickly!), this study looked at mineral fractions and leachates - two different things. The important distinction to be made between mineral separates and the leachates is that the mineral separates are the actual (primary?) minerals themselves, sans alteration minerals (I presume), and the leachates are the alteration minerals that dissolved in solution from the collected minerals.

Although I wasn't too clear on their exact method, it seems that rock sample crushed, minerals were collected, separated, and then placed in a solution to leach out the soluble minerals. The minerals left after the leaching process are termed the "mineral fractions." The minerals in solution are the "leachates."

It appears the leachate gives an indication of the alteration minerals that are formed from the primary minerals (as a result of some event), and judging from the fact that they are discussing shock impact textures, it was likely/possibly an impact event.

Therefore there was a very good chance that they would have contrasting analytical results/isochrons - and they did. It was expected based on petrographic anaylyses of the rocks, NOT ad hoc rationalizations as you claim. The authors have evidence at hand that the rocks were subjected to some sort of alteration event.

Also, please note that the discordant results were not discarded, but included in the report as they tell an important story. You simply don't agree with their interpretation.

This message has been edited by roxrkool, 12-10-2004 09:02 PM


This message is a reply to:
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JonF
Member
Posts: 6174
Joined: 06-23-2003


Message 65 of 113 (167027)
12-10-2004 5:15 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
So the study you quote is strong evidence against your claim that discordant results are suppressed.

I see no reason why you characterizse the explanations as "rationalizations" and "dubious" other than the fact that you don't like their primary conclusions.

There is no miraculous exemption of concordant data ... there are clear differences between the prcesses to which the mineral separates and the leachates have been exposed. That's the simplest and most likley explanation for the differences.

All in all, a nicely done paper in which the authors didn't claim too much, presented the data warts and all, and proposed explanations (and their reasons for those explanations) but didn't dogmatically i;nsist that they had the only possible explanations.

OTOH, there's no reason to believe that the problems encountered in this study are typical. So, here we are after 65 messages on five pages, and you have yet to adress the fundamental and fatal flaw in cour data and thesis: there's no valid way of extrapolating from your data (including this example) and the characteristics of the set of all dating studies because the data (and your most recent example) were specifically chosen so as to be notrepresentative of teh set of all dating studies.

I hope you adress that flaw over the weekend. I doubt you will.


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PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 66 of 113 (167033)
12-10-2004 5:27 PM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
Hi AC

Glad you took some advice and went out to find a real example. Hopefully we can discuss this paper in detail and this topic will remain as civil as it has so far.

I have read and re-read your critique and have also done the same for the paper that you cited.

My conclusions, however, do not match your own. To me the paper reads that the people who carried out the analysis took very great care to make sure that all of their results were "correct". Not fudged but genuinely correct.
I think some of your issues could be due to an incomplete knowledge of the processes involved in the analysis. Roxrkool explained some of it but let me give my slant on the analysis from the point of an analytical chemist. (not a geochronologist but someone who has analyzed a whole lot of rocks for chemical composition)

First I would like to say that there are parts of the paper that definitely lack adequate descriptions of methodology, particularly if you are not very familiar with analytical practices. (of course I have no idea of your own background so please excuse me if I am speaking out of line here)

I just intend to stick to my own area so let's look at the leacheates.

Leacheates are the liquid residue containing dissolved elements after a sample has been left to soak in the liquid for a period of time.


The mineral fractions were leached in warm 1N HCl for 10 minutes prior to digestion.

This is a fairly mild acid but is enough to dissolve some of the Rubidium and Sr which is easily available (not locked into crytaline structures) but doesn't come close to dissolving the locked in isotopes. That is done by the "digestion" that they mention

Why did they feel the need to leach the sample at all I wonder? It certainy isn't standard practice to soak a chunk of rock in warm acid prior to digestion. There had to be a valid pre-existing condition which they had noted in the sample in order to make it necessary.
Admittedly they didn't actually tell us the reason but if you know anything about sampling techniques then it is absolutely certain that they had one or they simply would not have done it.
It turns out that the paper does actually list this reason but you have to search a little to find it.

Rb and Sr in the host silicates may have been
fractionated and partitioned into leachable sites at ~90 Ma.

It is well known that only certain sites within the structure of the rock are leachable. Features on the rock's surface can often indicate that "shock" or some such event has occurred which would very likely have changed the chemical structure of certain parts of the rock, hence making the sites leachable.

It seems obvious to me that they must have foreseen that certain sites would be leachable or they would have had no reason to leach the rock at all. It would have been extremely bad science to have ignored this fact and carried on regardless. It should also be noted that leaching like this takes out such an infinitesimal amount of material from the parent rock that, had they not done it, the age of the bulk rock would not have changed by a measurable amount.
Therefore I would say that it speaks volumes for the integrity of these scientists that not only did they perform this "leach" but they reported it and explained it's completely predictable deviation from the primary isochron.
After all, there is a slight difference in the solubility between Rb and Sr.

I don't feel that I am qualified to comment in the defense of the actual age measurements. I am studying it in the attempt to become more familiar and knowledgable about this but (unlike chemical analysis techniques) it is still a little out of my field for now.

PY


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Replies to this message:
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Loudmouth
Inactive Member


Message 67 of 113 (167055)
12-10-2004 7:46 PM
Reply to: Message 66 by PurpleYouko
12-10-2004 5:27 PM


Re: An Example
quote:
It is well known that only certain sites within the structure of the rock are leachable. Features on the rock's surface can often indicate that "shock" or some such event has occurred which would very likely have changed the chemical structure of certain parts of the rock, hence making the sites leachable.

The rock samples being tested are actually meteors from Mars, literally. They suspected metamorphosis from the shock of the meteor hitting the earth, not a bad assumption given the speed with which meteor can strike the earth. I am definitely not an expert in geologic methodologies, but assuming that shock metamorphisis could have occured is far from an ad hoc hypothesis, or "arbitrary" as AC seems to indicate.


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Replies to this message:
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 Message 69 by roxrkool, posted 12-10-2004 9:35 PM Loudmouth has not replied
 Message 84 by Anti-Climacus, posted 12-14-2004 6:50 PM Loudmouth has replied

  
dpardo
Inactive Member


Message 68 of 113 (167059)
12-10-2004 8:19 PM
Reply to: Message 67 by Loudmouth
12-10-2004 7:46 PM


Re: An Example
Loudmouth writes:

The rock samples being tested are actually meteors from Mars, literally.

Can you elaborate on this?


This message is a reply to:
 Message 67 by Loudmouth, posted 12-10-2004 7:46 PM Loudmouth has not replied

Replies to this message:
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roxrkool
Member (Idle past 299 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 69 of 113 (167072)
12-10-2004 9:35 PM
Reply to: Message 67 by Loudmouth
12-10-2004 7:46 PM


Re: An Example
haha DUH!!! I read they were martian rocks and then totally spaced that off.

I'm still unclear as to the nature of the leachate parent material. I can't tell if they originate from actual alteration minerals or not, but PurpleYouKo's post made a lot of sense.

The paper reads as though it is part of a larger set of related research. I feel like I'm reading it out of context.

Oh yeah, I forgot to add that it's possible the shock textures are the result of having been ejected into space from Mars, too. There was likely an impact on Mars that caused the meteorites to be ejected in the first place.

Damn! Cora beat me to it.

This message has been edited by roxrkool, 12-10-2004 09:51 PM

This message has been edited by roxrkool, 12-10-2004 09:52 PM


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roxrkool
Member (Idle past 299 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 70 of 113 (167073)
12-10-2004 9:37 PM
Reply to: Message 68 by dpardo
12-10-2004 8:19 PM


Re: An Example
This is the first part of the synopsis:

Synopsis: We have completed Rb-Sr isotopic analyses on
mineral fractions and leachates from the Martian meteorite
LEW88516 (LEW). This meteorite is classified as a lherzolitic
shergottite and is mineralogically and geochemically
very similar to the other two lherzolitic shergottites
ALH77005 (ALH) and Y793605 (Y79) [1,2,3,4].

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Coragyps
Member (Idle past 45 days)
Posts: 5553
From: Snyder, Texas, USA
Joined: 11-12-2002


Message 71 of 113 (167075)
12-10-2004 9:41 PM
Reply to: Message 68 by dpardo
12-10-2004 8:19 PM


Re: An Example
Shergottites are one of about three kinds of meteorites that have isotope ratios in the gas bubbles trapped inside that very closely matching ratios known to exist in Mars's atmosphere - and very unlike Earth's. The shock features that they show very possibly are from the impact that knocked them loose from Mars, not from hitting Earth. Smallish meteorites get slowed pretty well by our atmosphere. But it takes a pretty good knock by a meteor hitting Mars to propel fragments upward at greater than escape velocity.

This message has been edited by Coragyps, 12-10-2004 09:44 PM


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PurpleYouko
Member
Posts: 714
From: Columbia Missouri
Joined: 11-11-2004


Message 72 of 113 (167089)
12-10-2004 11:26 PM
Reply to: Message 71 by Coragyps
12-10-2004 9:41 PM


Re: An Example
I think that one of the ways that they help to identify meteorites from other planets like Mars is due to their relatively young age.
Again I am no expert but I hear that most meteorites that come from ateroid collisions etc. come in at around 4.5Ga (the same age as the solar system and a little older than terrestrial rock)

Meteorites from Mars could well have been ejected from the planet as molten rock after a major impact. (speculation) This would have reset their clocks so that 170Ma would be the period since the impact.

Visible impact stress marks are probably from the meteorite hitting the Earth. Not sure how this would hold up for the martian atmosphere gas bubbles. Maybe dissolved martian atmospheric gas could have been present prior to recrystalisation.

Just a thought. Any experts out there know?

PY


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roxrkool
Member (Idle past 299 days)
Posts: 1497
From: Nevada
Joined: 03-23-2003


Message 73 of 113 (167092)
12-11-2004 12:00 AM
Reply to: Message 72 by PurpleYouko
12-10-2004 11:26 PM


Re: An Example
According to a few talks I went to on Mars, I seem to remember a reason for studying Martian rocks is to learn a little about earth's earliest geologic history. Mars appears to have been preserved quite early in its geologic history and perhaps we could learn from Mars what's been erased on Earth.

This message is a reply to:
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NosyNed
Member
Posts: 8971
From: Canada
Joined: 04-04-2003


Message 74 of 113 (167118)
12-11-2004 1:40 AM
Reply to: Message 68 by dpardo
12-10-2004 8:19 PM


Elaborate?
Can you elaborate on this?

I don't understand why you have asked for this. I don't know if those who have answered are giving you what you want.

A strange question to me.

It is however, very relevant. This is a hunk of rock that has "been through a lot" as they say.

From that one would expect to have to be careful in what you are dating. The whole paper seems to make that rather clear.


This message is a reply to:
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PaulK
Member
Posts: 17178
Joined: 01-10-2003
Member Rating: 2.6


Message 75 of 113 (167135)
12-11-2004 5:34 AM
Reply to: Message 60 by Anti-Climacus
12-10-2004 2:36 PM


Re: An Example
It seems that your primary point is that you reject the explanations offered by geologists for "discordant" dates. However I do beleive that you need to provide strong evidence that the explanations offered are incorrect or automatically available in all cases.

Unfortunately I do not see how this could possibly back up your original argument at all, even if it were to be demonstrated that your opinion was correct in this matter. It supports neither of the claims that your original post was meant to do. In my view it would have been far better if you had offered a clear explanation of how your alleged "predictions" are derived from the creationist paradigm and then provided evidence for them.

While others have raised reasonable points I would like to ask why you insist that the two meteorites must be samples, ultimmately derived from the same source. In addition I would like you to explain why you think that this argument would be easily available to geologists dealing with terrestrial sources and especially what evidence you have that the trace element differences used to support the idea are common enough that such evidence would usually be available.

In addition I would like to know why you consider the reference to the potential problems caused by shock melts an example of "preparing excuses in advance". After all even if excuses were prepared in advance there would be no need to report them in the paper The fact that they were mentioned is surely better interpreted as indicating that the authors thought that there was a strong possibility that they would not obtain a valid isochron. If geologists routinely make excuses there should be no surprise that excuses prepared in advance were not needed and certainly no need to express surprise at such an event. This part then is surely evidence against your assertions, not evidence for them.


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