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Author Topic:   Radioactive carbon dating
kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 118 of 221 (407228)
06-25-2007 7:44 AM
Reply to: Message 116 by Percy
06-24-2007 10:07 PM


Re: A response to various criticisms
It looks like there's been a lot of nonsense spouted in this thread. I'll respond to just one of the many issues at the moment:
quote:
quote:
I won't waste any time stating too much how Potassium-Argon is a failure at dating recent igneous rock from lava flows.

Of course it's a failure. By definition it has to be a failure at measuring the age of recent materials. The long half-life of 40K (over a billion years) means that it is really only effective for material older than about 100,000 years, and even that would be straining the technique a bit. It's best used on materials at least a million years old. Using K/Ar dating on a recent lava flow would be like using a yardstick to measure the width of a human hair.
quote:
At the very least, geologists admit it doesn't work on volcanoes,...

Hopefully you're referring again to recent volcanoes. K/Ar dating is one of the most important tools in the geologist's kit for dating ancient volcanic flows.

The best-known "failures" of K-Ar were intentional. When the 39Ar-40Ar method was invented, scientists wanted to test it where they thought traditional K-Ar would fail. So they intentionally tried to date recent submarine lava flows off the coast of Hawaii, the theory being that the water would have cooled the lava so fast that it would incorporate initial "parentless" argon, throwing off the dates. Sure enough, the traditional K-Ar dated very old, but the new method correctly gave dates consistent with "recent".

Some young earth creationists picked up these articles and began quoting the erroneous K-Ar dates as evidence of the method's failure, completely missing the point of the research and ignoring the correct 39Ar-40Ar dates.

Note that there should be no problem using K-Ar for even recent lava flows, as long as it does not have parentless argon. But the error bars will be large, so it won't be too useful.


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kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 119 of 221 (407229)
06-25-2007 8:20 AM
Reply to: Message 104 by fooj
06-24-2007 2:40 PM


Re: Two types of nuclides and Potassium Argon dating
I found this article about Potassium Argon at common sense science dot org. I don't think it proposes accelerated radioactive decay, but it does seem to imply that any given magma containing potassium-argon was hot enough to produce short half-life k40 isotopes which are hard to distinguish from full half life k40 isotope elements. I wonder if they have made more progress in this direction.

They suggest that somehow this "short half-life" 40K accounts for old dates of recent lava flows. This doesn't make any sense. It would imply:
1) the hypothesized "short half life" 40K must be present in volcanic flows, so it must be present in magma. Since its half-life is so short, to be present in the magma at any concentration it must be continually created somehow. But how? From what? If from normal K-40, it would quickly deplete the amount of K-40. And this would throw off the 39K-40K ratio, and we would see evidence of it.
2) this would affect 39Ar-40Ar dates as well as traditional K-Ar dates, so both would give old dates for recent lava flows. But this is not consistent with the data. Parentless argon explains the data much better.

They hypothesize something for which there is no experimental evidence, and which seems to be inconsistent with the data. It sounds like nonsense.


This message is a reply to:
 Message 104 by fooj, posted 06-24-2007 2:40 PM fooj has responded

Replies to this message:
 Message 124 by kbertsche, posted 06-25-2007 1:29 PM kbertsche has acknowledged this reply
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kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 124 of 221 (407271)
06-25-2007 1:29 PM
Reply to: Message 119 by kbertsche
06-25-2007 8:20 AM


Re: Two types of nuclides and Potassium Argon dating
I'm going to reply to myself to correct/modify my earlier statement:
2) this would affect 39Ar-40Ar dates as well as traditional K-Ar dates, so both would give old dates for recent lava flows. But this is not consistent with the data. Parentless argon explains the data much better.

This is probably not correct. The hypothesized new form of 40K supposedly has a 12-hr half-life. If it takes much longer than this for the lava to cool and crystalize (which is almost certainly the case), any 40Ar from this new type of 40K will have already decayed, will not be incorporated into the crystal lattice, and will look just like parentless 40Ar. In this case, 39Ar-40Ar will still give the correct dates.


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 Message 119 by kbertsche, posted 06-25-2007 8:20 AM kbertsche has acknowledged this reply

    
kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 125 of 221 (407274)
06-25-2007 1:39 PM
Reply to: Message 123 by JonF
06-25-2007 12:59 PM


Re: A response to various criticisms
Actually, U-Th-Pb dating, mostly U-Pb in zircons, is used in over half the geologic dating studies. K-Ar and Ar-Ar combined are around 30%. YECs don't like to address U-Th-Pb dating 'cause it's so robust. K-Ar has the potential of error, especialy when purposefuly misappied by YECs, but it's well-understood and low cost, so it's still useful.

Ar-Ar is also very robust. My former colleagues used this for crater dating studies; they ONLY used Ar-Ar dates, not K-Ar, because Ar-Ar can give narrow and reliable error bars (much better than K-Ar). I've never seen the YEC's address this method, either.


This message is a reply to:
 Message 123 by JonF, posted 06-25-2007 12:59 PM JonF has responded

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kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 149 of 221 (407337)
06-25-2007 6:51 PM
Reply to: Message 131 by fooj
06-25-2007 4:33 PM


Re: A response to various criticisms
I wonder if there are details which are left out. It could be because my background in physics is admittedly weak, but I can make sense of every number in the chart and document. They could also be understating the evidence by not mentioning every measurement. It happens.

I don't see any evidence that the authors of the paper have taken ANY measurements. They are simply proposing a theory and computer model, and showing the results, along with tabulated data.

And if the potassium and argon was made in magma, it would be hard to date it at all accurately.

Not true! When the molten magma solidifies and crystalizes, initial Ar is pushed to crystal grain boundaries since it cannot chemically bond in a crystal structure. The 40K that IS incorporated into the crystal lattice slowly decays, leaving 40Ar stuck in the crystal lattice. The 39Ar-40Ar method is able to distinguish between Ar that is at grain boundaries and Ar that is trapped within the crystal lattice, so it gives accurate dates even in this case. Someone else has already posted links to some experimental data for this.


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kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 158 of 221 (457877)
02-26-2008 1:21 AM
Reply to: Message 154 by Chiroptera
11-30-2007 7:51 PM


Re: From SophistiCat on Age Correlations.
FYI, a short rebuttal of RATE's radiocarbon claims, an early version of which started a spirited discussion with Baumgardner on TheologyWeb, has just been published in Perspectives on Science and Christian Faith. It can be seen here:
http://www.asa3.org/ASA/education/origins/rate-pscf.htm#4

An expanded analysis of the RATE claims, about 5x longer, is also available here:
http://www.asa3.org/ASA/education/origins/carbon-kb.htm

Kirk Bertsche


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kbertsche
Member
Posts: 1062
From: San Jose, CA, USA
Joined: 05-10-2007


Message 162 of 221 (504283)
03-26-2009 10:36 AM
Reply to: Message 161 by Coyote
03-23-2009 12:42 AM


Re: carbon dating and the "equilibrium" problem for Daniel4140
quote:

The "equilibrium problem" comes from websites like AnswersinGenesis:
http://www.answersingenesis.org/articles/nab/does-c14-disprove-the-bible


From the AiG link:
It is assumed that the ratio of 14C to 12C in the atmosphere has always been the same as it is today (1 to 1 trillion). ... If the production rate of 14C in the atmosphere is not equal to the removal rate (mostly through decay), this ratio will change. In other words, the amount of 14C being produced in the atmosphere must equal the amount being removed to be in a steady state (also called “equilibrium”). If this is not true, the ratio of 14C to 12C is not a constant, which would make knowing the starting amount of 14C in a specimen difficult or impossible to accurately determine.

Dr. Willard Libby, the founder of the carbon-14 dating method, assumed this ratio to be constant.


This is partly true, but the facts are being twisted. Yes, Libby assumed equilibrium. An equilibrium assumption works surprisingly well (maximum error less than 15% over the last 45,000 years) due to our large atmospheric and terrestrial carbon reservoirs which dilute the effects of non-equilibrium production rates.

But with tree ring calibrations, equilibrium does NOT need to be assumed. The only assumptions are that 1) we can count annual tree rings, and 2) the trees used for calibration and the unknowns breathed the same atmospheric radiocarbon. There is NO assumption of equilibrium, original concentrations, etc. (BTW, this also gets around any claims of changes in the decay rate.)

These details are mostly unknown by YECs, who persist in claiming that radiocarbon rests on many unproven assumptions. I was quizzed on this just last week by a fairly knowledgeable YEC, who seemed surprised by these details.

Edited by kbertsche, : No reason given.


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