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Author Topic:   Earth science curriculum tailored to fit wavering fundamentalists
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 106 of 1053 (750716)
02-21-2015 9:10 AM
Reply to: Message 102 by NoNukes
02-21-2015 2:27 AM


NoNukes writes:
The word 'compared' in the following sentence (Emphasis added by me) means to take a ratio:
Yes, but it appears to me that the 'comparison' they are making is not between C14 and C12, but between the C14 in the aged sample with the C14 in a theoretical un-aged sample. That's how I'm reading the sentence anyway (and I could be reading it wrong).
quote:
where ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years).
JB

This message is a reply to:
 Message 102 by NoNukes, posted 02-21-2015 2:27 AM NoNukes has replied

Replies to this message:
 Message 109 by NoNukes, posted 02-21-2015 10:09 AM ThinAirDesigns has replied

  
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 107 of 1053 (750717)
02-21-2015 9:19 AM


I'd like to make a generic statement to everyone on this thread. Y'all are being SO freaking generous with your time and efforts and I really appreciate that. Having said that, I've never learned a damn thing in my life by nodding and pretending to understand an answer if the answer doesn't yet make sense to me.
Please don't take what might appear as push-back against an answer as hubris or a lack of appreciation. I don't know shit about this stuff, but I won't learn about it if I pretend I understand an answer when I don't. Push-back is not me saying "I'm right and you're wrong.", it's me saying "My understanding says "A" and you're telling me "B". I assume "B" is correct because you have experience in the field and I do not, but I need to figure out how to get my own knowledge from my current understanding ("A") to the correct one ("B").
I also know that it's not your job to make me understand. As I've said before in selective cases where I was the one attempting to help someone out to no avail -- "I can only explain it to you, I can't make you understand it.".
Thanks again.
JB

  
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 108 of 1053 (750720)
02-21-2015 9:48 AM
Reply to: Message 104 by ThinAirDesigns
02-21-2015 8:58 AM


ThinAirDesigns writes:
The data I downloaded was a comma delimited file with 5 fields (and no header).
So I found a link that gives me a virtual header for the data I downloaded.
http://www.radiocarbon.org/IntCal13.htm
Column values are as follows.
quote:
Format: cal BP, 14C BP, Error, Δ14C (), σ14C
So my assumption related to the first column being calendar was correct and RAZD helpfully educated my on the correct value of the zero year.
Thanks
JB

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NoNukes
Inactive Member


Message 109 of 1053 (750722)
02-21-2015 10:09 AM
Reply to: Message 106 by ThinAirDesigns
02-21-2015 9:10 AM


Yes, but it appears to me that the 'comparison' they are making is not between C14 and C12, but between the C14 in the aged sample with the C14 in a theoretical un-aged sample.
Assuming that to be true, then the comparison is still a ratio, which is the question that you asked. But in what units is the C14 measured? Clearly when taking a ratio, the two units of measure must be the same. Let's focus on what is being compared...
quote:
percent of carbon-14 in the sample compared to the amount in living tissue
To take a ratio, or to make a meaningful comparison, both of these numbers must be expressed in the same units, or in the same non unit quantity such as percent, or some other fraction relating the C14 and C12. The term 'amount' must be taken as meaning the same type of number as the percentage, or we cannot meaningfully make a comparison. So what is being described here is actually a ratio of ratios. (Or a ratio of percentages since a percentage is also a ratio)
Perhaps the word amount is giving you difficulty as it could suggest a bulk measurement.

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This message is a reply to:
 Message 106 by ThinAirDesigns, posted 02-21-2015 9:10 AM ThinAirDesigns has replied

Replies to this message:
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ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 110 of 1053 (750725)
02-21-2015 10:37 AM
Reply to: Message 109 by NoNukes
02-21-2015 10:09 AM


NoNukes writes:
Assuming that to be true, then the comparison is still a ratio, which is the question that you asked.
Nope, I didn't asked generically about "a ratio", but specifically about the ratio between C14 and C12 (See green in below quote).
quote:
One thing I'm a bit confused about is the sources seem almost evenly split between describing the ratio between C14 and C12 as part of the measurement process and saying nothing about ratio and merely talking about measuring the C14.
I'm trying to figure out if
A: the ratio is relevant
B: if relevant, how is the ratio used.
NoNukes writes:
Perhaps the word amount is giving you difficulty as it could suggest a bulk measurement.
What's giving me difficulty is there being a common statement that a ratio between two different isotopes (C12 to C14) is part of the dating process and then a formula is posted where the ratio actually being measured (as I understand it) is between ONE isotope (original C14 to current C14).
Just to refresh, here is the section of the link that is confusing me:
quote:
Dating a Fossil
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely.
A formula to calculate how old a sample is by carbon-14 dating is:
t = [ ln (Nf/No) / (-0.693) ] x t1/2
t = [ ln (Nf/No) / (-0.693) ] x t1/2
where ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years).
So, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be:
t = [ ln (0.10) / (-0.693) ] x 5,700 years
t = [ (-2.303) / (-0.693) ] x 5,700 years
t = [ 3.323 ] x 5,700 years
t = 18,940 years old
Perhaps that formula is wrong. Perhaps the ratio between C14 and C12 isn't used. Perhaps I'm blind. I'm not sure what I'm missing, but I can't find anyplace in that formula where C12 is represented in any form. If both C12 and C14 are compared as is clearly stated, wouldn't both C14 and C12 have to be represented in the formula?
JB

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RAZD
Member (Idle past 1512 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 111 of 1053 (750728)
02-21-2015 11:28 AM
Reply to: Message 97 by ThinAirDesigns
02-20-2015 7:00 PM


One thing I'm a bit confused about is the sources seem almost evenly split between describing the ratio between C14 and C12 as part of the measurement process and saying nothing about ratio and merely talking about measuring the C14.
I'm trying to figure out if
A: the ratio is relevant
B: if relevant, how is the ratio used.
Consider that the amount of 12C is dependent on the size of the sample and the density of the carbon in the sample, so the same would apply to undecayed 14C (organic take-up of carbon is non-selective of isotopes), so to remove this variable from the testing the amount of 14C is compared to the amount of 12C.
So in the above example (green background portion) it clearly talks about comparing the *ratio of carbon-14 to carbon-12* in the sample to the *ratio* in the living organism and using that to date. But yet when I look at the formula provided, I don't see any utilized ratio, only the %C14 is input to the formula. What am I missing?
As this site was designed for kids to be able to understand (the whole "howstuffworks" site is great in that regard), it is a little simplified.
That formula is the standard radioactive decay formula that can be used for any radioactive isotope. As noted we can use %14C/12C and the formula works. Think of it this way ...
t = [ ln (Nf/No) / (-0.693) ] x t1/2
Nf = (14C/12C)f
No =(14C/12C)o
So
(14C/12C)f
(14C/12C)o
Becomes
(14C)f/(12C)
(14C)o/(12C)
Becomes
(14C)f
(14C)o
There are a couple of squirrely aspects to 14C dating, this is one (and it could be an interesting exercise to run through how you do end up with Nf/No with the kids) -- another is that the modern measured decay half life is not used in dating, rather the original half-life estimated by Libby is used. This is so new dates of artifacts can be compared to old ones without confusion with which rate was used, and because they are then corrected with the calibration curve (that uses the old rate) and they want to avoid making a correction twice.
The method (another good site)
quote:
Libby, Anderson and Arnold (1949) were the first to measure the rate of this decay. They found that after 5568 years, half the C14 in the original sample will have decayed and after another 5568 years, half of that remaining material will have decayed, and so on (see figure 1 below). The half-life (t 1/2) is the name given to this value which Libby measured at 5568+/-30 years. This became known as the Libby half-life. After 10 half-lives, there is a very small amount of radioactive carbon present in a sample. At about 50 - 60 000 years, then, the limit of the technique is reached (beyond this time, other radiometric techniques must be used for dating). By measuring the C14 concentration or residual radioactivity of a sample whose age is not known, it is possible to obtain the countrate or number of decay events per gram of Carbon. By comparing this with modern levels of activity (1890 wood corrected for decay to 1950 AD) and using the measured half-life it becomes possible to calculate a date for the death of the sample.
bold added
Radiocarbon Date calculation
quote:
The Conventional Radiocarbon Age BP is calculated using the radiocarbon decay equation:
t=-8033 ln(Asn/Aon)
Where -8033 represents the mean lifetime of 14C (Stuiver and Polach, 1977). Aon is the activity in counts per minute of the modern standard, Asn is the equivalent cpm for the sample. 'ln' represents the natural logarithm.
A CRA embraces the following recommended conventions:
  • a half-life of 5568 years;
  • the use of Oxalic acid I or II, or appropriate secondary radiocarbon standards (e.g. ANU sucrose) as the modern radiocarbon standard;
  • correction for sample isotopic fractionation (deltaC13) to a normalized or base value of -25.0 per mille relative to the ratio of C12/C13 in the carbonate standard VPDB (more on fractionation and deltaC13);
  • the use of 1950 AD as 0 BP, ie all C14 ages head back in time from 1950;
  • the assumption that all C14 reservoirs have remained constant through time.

bold added
Modern measurements put the half-life at 5730 years. This is not a problem as long as both calculated dates are calibration curves use the same half-life of 5568.
Another way to think about it is that the calculated 14C date is actually a measurement of the percentage of 14C compared to 12C in the sample, which is then correlated with tree ring 14C/12C percentages to give an approximated age.
Enjoy
Edited by RAZD, : clrty

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This message is a reply to:
 Message 97 by ThinAirDesigns, posted 02-20-2015 7:00 PM ThinAirDesigns has replied

Replies to this message:
 Message 113 by ThinAirDesigns, posted 02-21-2015 11:39 AM RAZD has replied

  
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 112 of 1053 (750729)
02-21-2015 11:31 AM
Reply to: Message 109 by NoNukes
02-21-2015 10:09 AM


NoNukes, I'm reading furiously every link I can find trying to make sense of my question and your answer. I'm not yet ready to say I'm there, but your answers have allowed me to do better searches and I feel I'm starting to understand your answer better.
Currently it appears that when they say 'percent C14' in the sample, it's implied that the percent is measured against the C12 so that's how C12 is represented in the formula. I think I'm right on that and I'm pretty sure that is what you were trying to get across to me. Still working on it.
More later, but thanks
JB

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ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 113 of 1053 (750730)
02-21-2015 11:39 AM
Reply to: Message 111 by RAZD
02-21-2015 11:28 AM


Thanks RAZD,
Yeah, I can see from your formula what is happening there with the C14/C12. The link I was reading merely used a simplified version of the formula and NoNukes was trying to get that through my thick skull.
And yeah I've read about the updated half life numbers. I assume that IntCal takes the updated half life into account? In other words, using IntCal13 you can take a C14 date, cross reference it and no other calibrations are required?
Thanks
JB

This message is a reply to:
 Message 111 by RAZD, posted 02-21-2015 11:28 AM RAZD has replied

Replies to this message:
 Message 114 by RAZD, posted 02-21-2015 11:54 AM ThinAirDesigns has replied

  
RAZD
Member (Idle past 1512 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 114 of 1053 (750733)
02-21-2015 11:54 AM
Reply to: Message 113 by ThinAirDesigns
02-21-2015 11:39 AM


And yeah I've read about the updated half life numbers. I assume that IntCal takes the updated half life into account? In other words, using IntCal13 you can take a C14 date, cross reference it and no other calibrations are required?
No, they still use the OLD half-life for the correlation curves. This is so any sample, old or new can be compared on the correlation curve to get a calibrated date. Like I said, squirely).
What you actually have with a 14C date is a measure of 14C/12C plotted on a log scale and the "14C dates" can be converted back to 14C/12C numbers, at which point the half-life is irrelevant to the correlation and the calibrated date. Here is an example of this approach that I believe I posted this before:
Christian Geologists on Noah's Flood: Biblical and Scientific Shortcomings of Flood Geology, part 4
quote:
We will employ tree rings and carbon-14, but not in the way readers may be accustomed to seeing. We will not use carbon-14 to determine an age at all. We will simply measure how much carbon-14 is currently found in each tree ring. Carbon-14 decays with time, so if each tree ring represents one year of growth, we should see a steady decline in the carbon-14 content of each successive ring. Figure 5 shows tree-ring carbon-14 data from living trees extending back 4000 rings.[2] ...

Does that help?
Enjoy

we are limited in our ability to understand
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RebelAmerican☆Zen☯Deist
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This message is a reply to:
 Message 113 by ThinAirDesigns, posted 02-21-2015 11:39 AM ThinAirDesigns has replied

Replies to this message:
 Message 115 by ThinAirDesigns, posted 02-21-2015 12:08 PM RAZD has replied

  
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 115 of 1053 (750734)
02-21-2015 12:08 PM
Reply to: Message 114 by RAZD
02-21-2015 11:54 AM


Ok, so in addition to IntCal13, there is an ~1.03 (5730/5568) correction that still must be made.
And yes, that helped.
Appreciate you, NoNukes, Coyote and Dr Adequate helping me get it straight.
JB
Edited by ThinAirDesigns, : No reason given.

This message is a reply to:
 Message 114 by RAZD, posted 02-21-2015 11:54 AM RAZD has replied

Replies to this message:
 Message 116 by Coyote, posted 02-21-2015 12:45 PM ThinAirDesigns has replied
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Coyote
Member (Idle past 2213 days)
Posts: 6117
Joined: 01-12-2008


Message 116 of 1053 (750736)
02-21-2015 12:45 PM
Reply to: Message 115 by ThinAirDesigns
02-21-2015 12:08 PM


I have never bothered with that 1.03 correction. I just use the calibrated range and intercept.
And I have done over 650 dates in my research area, and have nearly 7,000 dates in my computer.

Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
Belief gets in the way of learning--Robert A. Heinlein
How can I possibly put a new idea into your heads, if I do not first remove your delusions?--Robert A. Heinlein
It's not what we don't know that hurts, it's what we know that ain't so--Will Rogers
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If a religion's teachings are true, then it should have nothing to fear from science...--dwise1
"Multiculturalism" demands that the US be tolerant of everything except its own past, culture, traditions, and identity.

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ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 117 of 1053 (750738)
02-21-2015 1:01 PM
Reply to: Message 116 by Coyote
02-21-2015 12:45 PM


Yeah, I get it. The truth of all this is that for YEC purposes, one doesn't have to do any calibration corrections at all.
That's the thing I want to make clear to the kids. All this talk on the YEC sites about equilibrium assumptions killing RC dating are BS in at least 2 ways:
1: scientists DON'T assume equilibrium in atmospheric C14.
2: even if they did it wouldn't freaking matter to the YEC argument.
But I do like to understand how it all fits together so when they ask questions I can answer intelligently and knowledgeably.
Thanks again. Y'all.
JB
Edited by ThinAirDesigns, : No reason given.

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RAZD
Member (Idle past 1512 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 118 of 1053 (750740)
02-21-2015 1:38 PM
Reply to: Message 115 by ThinAirDesigns
02-21-2015 12:08 PM


Ok, so in addition to IntCal13, there is an ~1.03 (5730/5568) correction that still must be made.
Actually no, unless what you want is a slightly more accurate calculated 14C date. When you use the calibration curve it corrects for (a) the variation in atmospheric 14C at the time the ring (sample) formed due to cosmogenic variations, and (b) the difference from raw 14C date (with old half-life) to actual tree ring date.
Correcting the raw date to 5730 from 5568 and then entering the calibration curve would mean you have corrected it twice.
Message 117: Yeah, I get it. The truth of all this is that for YEC purposes, one doesn't have to do any calibration corrections at all.
More to the point, when the corrections are made the artifact dates become older.
That's the thing I want to make clear to the kids. All this talk on the YEC sites about equilibrium assumptions killing RC dating are BS in at least 2 ways:
1: scientists DON'T assume equilibrium in atmospheric C14.
Correct. An old YEC argument I remember was that 14C is unreliable because not enough time has passed for 14C to reach an equilibrium level (which has to do with chain decay in other radiometric isotopes).
2: even if they did it wouldn't freaking matter to the YEC argument.
See
An Index to Creationist Claims PRATT list
(points refuted a thousand times)
CD011.1: Carbon-14 Variability
Enjoy

we are limited in our ability to understand
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RAZD
Member (Idle past 1512 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 119 of 1053 (750743)
02-21-2015 2:24 PM
Reply to: Message 105 by ThinAirDesigns
02-21-2015 9:02 AM


Do you know if the field that is incremented steadily is the calendar dates and the one with scatter is the C14, or is the lookup table the other way around where you look up your C14 date on the steadily incremented column and then it gives you the actual date in the column with the scatter?
Actually the incremental axis would be the raw calculated 14C age (the information you have available) and the scatter would be due to the year to year variation in original atmospheric levels of 14C and the number of possible matches for that level of 14C, the standard deviation comes from measurement error and they introduce some smoothing of the data that doesn't really affect the results significantly. You need to see it graphically for clarity:
Again from my material for updating the age correlation thread:
Radiocarbon-Based Chronology for Dynastic Egypt (OK = Old Kingdom):
quote:
... Radiocarbon dating, which is a two-stage process involving isotope measurements and then calibration against similar measurements made on dendrochronologically dated wood, usually gives age ranges of 100 to 200 years for this period (95% probability range) and has previously been too imprecise to resolve these questions.
Here, we combine several classes of data to overcome these limitations in precision: measurements on archaeological samples that accurately reflect past fluctuations in radiocarbon activity, specific information on radiocarbon activity in the region of the Nile Valley, direct linkages between the dated samples and the historical chronology, and relative dating information from the historical chronology. Together, these enable us to match the patterns present in the radiocarbon dates with the details of the radiocarbon calibration record and, thus, to synchronize the scientific and historical dating methods. ...
... We have 128 dates from the NK, 43 from the MK, and 17 from the Old Kingdom (OK). The majority (~75%) of the measurements have calibrated age ranges that overlap with the conventional historical chronology, within the wide error limits that result from the calibration of individual dates.
The modeling of the data provides a chronology that extends from ~2650 to ~1100 B.C.E. ...
This figure shows the distribution of uncalibrated radiocarbon dates against the modeled age. For each measurement, we show the mean and 1σ of the radiocarbon and modeled calendar dates: ... The calibration curve is shown as two black lines (1σ ). ...
The results for the OK, although lower in resolution, also agree with the consensus chronology of Shaw (18) but have the resolution to contradict some suggested interpretations of the evidence, such as the astronomical hypothesis of Spence (24), which is substantially later, or the reevaluation of this hypothesis (25), which leads to a date that is earlier. The absence of astronomical observations in the papyrological record for the OK means that this data set provides one of the few absolute references for the positioning of this important period of Egyptian history (Fig. 1A).
Note that there are several other sample dates with similar correlation of 14C measurement to dendrochronology correlations, here it is the earliest/oldest set that is of interest as a measure of accuracy and precision. The dendrochronology correlation is shown as two lines in Fig 2 (+1σ and -1σ )
The earliest/oldest dates in Fig 2 are shown at ~2660 BCE, with 7 samples placed together (with two more placed nearby). There are several possible matches for each of these samples, running from 2580 BCE to 2860 BCE -- due to the wiggle of the 14C amounts in that portion of the graph -- I get 5 possible matches for the lowest point with an average age of 2693 BCE, 8 possible matches for the next point with an average of 2660 BCE, 6 possible matches for the third point for an average of 2702 BCE, 12 possible matches for the fourth point for an average of 2733 BCE, 9 possible matches for the fifth point for an average of 2754 BCE, 6 possible matches for the sixth point for an average of 2750 BCE, 8 possible matches for the seventh point for an average of 2771 BCE, 8 possible matches for the eight point for an average of 2787 BCE, and 6 possible matches for the highest point for an average of 2788 BCE. Assuming these points all represent the same age, the overall average age is ~2740 BCE with σ of +/-88 years (2827 BCE to 2651 BCE). Shaw's date for the tomb is 2660 BCE, so this is in close agreement with that dating. Note that +/-88 years in over 4,700 years of tree ring chronology is an error of +/-1.9%. The error is partly due to the two stage process of using 14C data to convert to dendrochronological calendar age, but mostly due to the wiggle of the 14C levels that match these points.
Note that this conversion does not depend on the calculation of 14C 'age' -- that is a purely mathematical conversion of the measured amounts of 14C and 12C in the samples, and then comparing those 14C/12C values to ones found in the tree rings to find the best match to the tree rings, just as was done for the biblical history times above.
This does, however,introduce an extra source of error due to the number of rings that match those levels inside the +/-1σ margins of error.
Enjoy
Edited by RAZD, : clrty

we are limited in our ability to understand
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This message is a reply to:
 Message 105 by ThinAirDesigns, posted 02-21-2015 9:02 AM ThinAirDesigns has replied

Replies to this message:
 Message 120 by ThinAirDesigns, posted 02-21-2015 5:11 PM RAZD has replied

  
ThinAirDesigns
Member (Idle past 2480 days)
Posts: 564
Joined: 02-12-2015


Message 120 of 1053 (750749)
02-21-2015 5:11 PM
Reply to: Message 119 by RAZD
02-21-2015 2:24 PM


RAZD writes:
the incremental axis would be the raw calculated 14C age (the information you have available) and the scatter would be due to the year to year variation in original atmospheric levels of 14C and the number of possible matches for that level of 14C, ...
So I'm confused again - sorry, it happens a lot with me. LOL
Here is a link that provides a download of the IntCal13 data.
http://www.radiocarbon.org/IntCal13.htm
Here is the format they give for the data: I've 'red boxed' to two relevant portions of the image.
Top box = the format given in the description of the download link
Lower box = format from the actual header from the data file and a small portion of the data.
In both of those formats, they assign the evenly incrementing column to CalBp and the scattered one to 14C. What am I missing since you appear to be telling me the opposite is true?
You need to see it graphically for clarity:
Oh, I've got it charted 6 ways to Sunday already (that's why I downloaded it). I'll be posting some charts with related questions in a bit, but to know what to ask I have to figure out which column is which.
Thanks
JB

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 Message 123 by RAZD, posted 02-21-2015 8:21 PM ThinAirDesigns has replied

  
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