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Author Topic:   Earth science curriculum tailored to fit wavering fundamentalists
edge
Member (Idle past 1818 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(2)
Message 646 of 1053 (758465)
05-26-2015 1:07 PM
Reply to: Message 644 by petrophysics1
05-26-2015 10:27 AM


Re: C14 in Diamonds
This is how a Uranium roll front deposit works. The ground water containing a very small amount of U keeps moving until it hits an area which is a reducing environment and precipitates out. Over millions of years you end up getting a mineable Uranium deposit. There are hundreds if not thousands of these in the western US
In fact, the Oklo reactor that has been discussed here previously was probably formed by the same process and it reached not only minable grades but fissonable concentrations.
Natural nuclear fission reactor - Wikipedia
I might add that the roll front deposits and coal beds can be found in similar sedimentary environments such as exist on the Colorado Plateau and in Wyoming.

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kbertsche
Member (Idle past 2243 days)
Posts: 1427
From: San Jose, CA, USA
Joined: 05-10-2007


Message 647 of 1053 (758466)
05-26-2015 1:17 PM
Reply to: Message 640 by edge
05-25-2015 7:57 PM


Re: C14 in Diamonds
In fact, there are more abundant radioisotopes than those of uranium. Thorium is about 3 times as abundant, IIRC. Not only that, but we should probably be dealing with daughter products more than the uranium itself.
But we need neutrons to create C-14. I don't believe that Th or the U-Th daughter products can emit neutrons.
I think if we just look at the radon flux through coal beds for instance, we might come up with a very different viewpoint of what is happening.
If we could measure the Rn emission, we could get an independent estimate of the U content (and neutron flux) in the vicinity. This could be helpful.

"Science without religion is lame, religion without science is blind." — Albert Einstein
I am very astonished that the scientific picture of the real world around me is very deficient. It gives us a lot of factual information, puts all of our experience in a magnificently consistent order, but it is ghastly silent about all and sundry that is really near to our heart, that really matters to us. It cannot tell us a word about red and blue, bitter and sweet, physical pain and physical delight; it knows nothing of beautiful and ugly, good or bad, God and eternity. Science sometimes pretends to answer questions in these domains, but the answers are very often so silly that we are not inclined to take them seriously. — Erwin Schroedinger

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edge
Member (Idle past 1818 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 648 of 1053 (758467)
05-26-2015 1:45 PM
Reply to: Message 647 by kbertsche
05-26-2015 1:17 PM


Re: C14 in Diamonds
But we need neutrons to create C-14. I don't believe that Th or the U-Th daughter products can emit neutrons.
In fact, we need 'thermal' neutrons IIRC.
Here is how they source neutrons artificially:
"Neutrons are produced when alpha particles impinge upon any of several low atomic weight isotopes including isotopes of beryllium, carbon and oxygen. This nuclear reaction can be used to construct a neutron source by intermixing a radioisotope that emits alpha particles such as radium or polonium with a low atomic weight isotope, usually in the form of a mixture of powders of the two materials." Neutron source - Wikipedia
You probably don't need this, but for those of us who are nuclear physics-challenged, here is an example decay chain for U/Th:
If we could measure the Rn emission, we could get an independent estimate of the U content (and neutron flux) in the vicinity. This could be helpful.
As Petrophysicist indicates, this is a very difficult task, because of the dynamics of the system. However, I read an article that suggests a total flux from the earth of 0.75 atoms of Rn222 per cm2/s in continental areas. I would guess that local effects could be large.
(edit Ra to Rn...)
Edited by edge, : No reason given.
Edited by edge, : No reason given.

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NoNukes
Inactive Member


Message 649 of 1053 (758468)
05-26-2015 2:44 PM
Reply to: Message 642 by kbertsche
05-25-2015 11:21 PM


Re: C14 in Diamonds
Nonukes writes:
bad argument. sorry.
kbertsche writes:
I welcome any corrections that you can give to my argument!
The comment was not meant for you. I had initially posted a bad argument and deleted it. Sorry for the mixup.
Are you sure that you haven't mixed up these details? Do you have any references for the cross sections of an (alpha,n) reaction for B-11? I know that B-10 has a HUGE cross section (thousands of Barns) for the opposite reaction, (n, alpha).
Yes I am sure about this. I recalled this from my experience with startup sources used in naval reactors, but I checked before posting.
You should not be all that surprised that B-10 and B-11 have very nuclear properties. The cross section of B-11 for neutrons is negligible. B-11 if present would not interfere with neutron absorption by B-10, so I'm really curious about the relevance of your citation of the B-10 neutron absorption cross section as evidence that I mixed up the B-11 reaction. Yes we do use boron to absorb neutrons but primarily because of the B-10.
I don't see how boron helps; any boron in the coal would tend to absorb neutrons and reduce the number available to make C-14 from N-14.
Ill try to outline why this could work. Yes B-10 has a high cross section for neutrons (4000 barns?), but boron is only 20% of Boron. N-14 has a cross section of about 2 barns and is essentially all of the natural nitrogen. So there is maybe a 400 to 1 advantage for Boron vs Nitrogen absorption (assuming equal amounts of B and N and no direct shielding of nuclei). So a 2-3 orders of magnitude advantage to B. That would be the end of the issue for neutrons produced from spontaneous fission.
If we want to calculate the rate of neutron absorption by N-14, then of course the competition between B-10 and N-14 is important, but so is the fact that there are 7-10 orders of magnitude more alpha decays than spontaneous fissions that produce neutrons directly. The available neutrons (from the B11 alpha reaction) and thus the amount of C-14 production from such a source should dwarf the amount caused by spontaneous fission of U235 and U238. And that's even taking into account the presence of B-10.
Reference for the principle involved:
Startup neutron source - Wikipedia
quote:
Boron-11 can be added to the fuel; it emits neutrons by the (α,n) reaction to nitrogen-14. Deuterium in heavy water emits neutrons by (γ,n) reaction to 1H.[6]
And as has been noted, there are other light nuclei which undergo similar reactions in the presence of alpha. Some of those nuclei have relatively high natural abundances.
Edited by NoNukes, : No reason given.
Edited by NoNukes, : No reason given.

Je Suis Charlie
Under a government which imprisons any unjustly, the true place for a just man is also in prison. Thoreau: Civil Disobedience (1846)
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RAZD
Member (Idle past 1516 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 650 of 1053 (758471)
05-26-2015 4:30 PM
Reply to: Message 638 by kbertsche
05-25-2015 4:50 PM


Re: C14 in Diamonds
... But according to my calculations, the amounts are quite small. ...
All it needs is to be measurable and you get an age near the limit of 14C dating, which is what is usually reported.
Certainly with water concentrating U in carbon\coal this can increase the amounts in coal.
And thanks Petro, I had previously wondered what made U precipitate on speleothems. (as in Age of Grand Canyon and Cave Speleothems and Devil's Hole -- an extension to what is in my age correlations thread)
Enjoy

we are limited in our ability to understand
by our ability to understand
RebelAmerican☆Zen☯Deist
... to learn ... to think ... to live ... to laugh ...
to share.


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edge
Member (Idle past 1818 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


(1)
Message 651 of 1053 (758506)
05-27-2015 11:14 AM
Reply to: Message 650 by RAZD
05-26-2015 4:30 PM


Re: C14 in Diamonds
And thanks Petro, I had previously wondered what made U precipitate on speleothems. (as in Age of Grand Canyon and Cave Speleothems and Devil's Hole -- an extension to what is in my age correlations thread)
The difference being that, in speleothems, the uranium would be fixed as some kind of oxidized mineral as an efflorescence from aqueous solution. In coal, I would expect uranium to be in a reduced state.

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RAZD
Member (Idle past 1516 days)
Posts: 20714
From: the other end of the sidewalk
Joined: 03-14-2004


Message 652 of 1053 (758507)
05-27-2015 11:17 AM
Reply to: Message 635 by ThinAirDesigns
05-24-2015 6:32 PM


Re: Transitional fossil visual aid
I'm thinking of a great visual aid to help get people past the Crocoduck nonsense. I've used it in conversation and it's quite helpful and it seem so obvious that I'm thinking someone surely has put something together to illustrate the concept.
Nice concept. Should be some good material in family photo albums. We used to have a portrait of my great grands on my mother's side, and you could see the family resemblances. Unfortunately that and a number of family photos burned in a house fire (house totaled, no one hurt), so I don't have that information anymore (although we may have a photo of it).
Another analogy that has been used is taking snapshots of a person walking across the US: each snapshot shows the same person in a different location, the locations are within walking distance of the other locations for the time difference. This also shows the importance of location in space as well as time for connecting fossils.
It would be cool to combine the two -- a family that immigrates from one location to another with old photos to document the times and locations.
Enjoy

we are limited in our ability to understand
by our ability to understand
RebelAmerican☆Zen☯Deist
... to learn ... to think ... to live ... to laugh ...
to share.


Join the effort to solve medical problems, AIDS/HIV, Cancer and more with Team EvC! (click)

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ThinAirDesigns
Member (Idle past 2485 days)
Posts: 564
Joined: 02-12-2015


Message 653 of 1053 (758524)
05-27-2015 10:40 PM


Fossil Dating
I'm having trouble finding a succinct answer to a fossil dating question.
From my reading, I learn (generally)
A: Fossils are usually dated by dating the surrounding rocks
B: Igneous rock dates rather well.
C: Sedimentary rock doesn't date well.
D: Fossils are rarely found in igneous rock.
E: Fossils are commonly found in sedimentary rock
I think you see my question coming here: For fossils that are dated using rock (rather than the fossil itself), what would the common dating method be if you can't date the sedimentary rock that contains the fossil? Do you move up the layers until you can find something to date, move down the layers and do the same and then use that range for the fossil? You could narrow the range from that some I suppose with knowledge of what sort of sedimentary rock it is and our knowledge of how long those take to form.
Anyway, I think y'all understand my question.
Thanks
JB

Replies to this message:
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Coyote
Member (Idle past 2218 days)
Posts: 6117
Joined: 01-12-2008


Message 654 of 1053 (758525)
05-27-2015 10:49 PM
Reply to: Message 653 by ThinAirDesigns
05-27-2015 10:40 PM


Re: Fossil Dating
That area of Africa had a lot of volcanic activity, so there are ash and other volcanic layers all over the place.
You date the layer above the fossil and the one below it, and that gives you upper and lower limits. If those two limits are close together you have a pretty tight dating range. If far apart, you look for index fossils or something else to help narrow the range.
Rinse and repeat.

Religious belief does not constitute scientific evidence, nor does it convey scientific knowledge.
Belief gets in the way of learning--Robert A. Heinlein
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This message is a reply to:
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JonF
Member (Idle past 279 days)
Posts: 6174
Joined: 06-23-2003


Message 655 of 1053 (758545)
05-28-2015 8:03 AM
Reply to: Message 653 by ThinAirDesigns
05-27-2015 10:40 PM


Re: Fossil Dating
To expand a tad on Coyote's answer:
An index fossil is easily recognized and occurs over a relatively small time period. They are used to correlate, not actually date, different places. If sedimentary layers A and B, widely separated, both contain index fossil X they are close to the same age. If igneous layer C above layer A is 5 Mya and igneous layer D below layer B is 5.2 Mya, that gives a range of dates in which A and B must lie.
This is the source of the common YEC canard "The rocks date the fossils and the fossils date the rocks; that's circular reasoning."
Edited by JonF, : No reason given.

This message is a reply to:
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Replies to this message:
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edge
Member (Idle past 1818 days)
Posts: 4696
From: Colorado, USA
Joined: 01-09-2002


Message 656 of 1053 (758553)
05-28-2015 11:31 AM
Reply to: Message 655 by JonF
05-28-2015 8:03 AM


Re: Fossil Dating
To expand a tad on Coyote's andswer:
An index fossil is easily recognized and occurs over a relatively small time period. They are used to correlate, not actually date, different places. If sedimentary layers A and B, widely separated, both contain index fossil X they are close to the same age. If igneous layer C above layer A is 5 Mya and igneous layer D below layer B is 5.2 Mya, that gives a range of dates in which A and B must lie.
This is the source of the common YEC canard "The rocks date the fossils and the fossils date the rocks; that's circular reasoning."
A few additional comments on this subtopic...
Normally, we would consider sedimentary rocks as undateable by radiometric methods. However, if we were to date the actual mineral grains, we can come up with meaningful data. Some of these grains will be derived from pre-existing igneous rocks and will provide an idea of the age of the source of sedimentary detritus; hence establishing a maximum age for the sedimentary rock. In some cases, particularly in sedimentary rocks derived from volcanic rocks, the ages may be fairly close.
"As igneous rock erodes, the eroded particles are deposited to become sedimentary rock. Dating sedimentary rock by using radiometric techniques will tell the age of the original igneous rock, not the time since the sedimentary rock formed. (Although sometimes the two ages are very similar, for example when a volcanic explosion deposits ash on a surface and that ash is quickly incorporated into sediments. The age of the ash and the age of the sedimentary rock would then be very similar.) Metamorphic rock, by contrast, is formed from earlier rock through intense heat and pressure. Metamorphism can reset some radiometric clocks (Potassium-Argon is particularly susceptible), so that radiometric dates record the time of alteration rather than the date when the earlier rock first solidified from magma or was deposited as sediment. Other parent-daughter pairs are less susceptible to alteration." Paleobiology | Smithsonian National Museum of Natural History
Another possibility is the dating of cementing (authigenic) minerals within the sedimentary rocks ... a little more difficult, but under the right circumstances, possible.
"Xenotime (YPO4) is an isotopically robust chronometer, which is increasingly being recognized as a trace constituent in siliciclastic sedimentary rocks. http://www.sciencedirect.com/...rticle/pii/S0012825204000558

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JonF
Member (Idle past 279 days)
Posts: 6174
Joined: 06-23-2003


Message 657 of 1053 (758578)
05-28-2015 1:40 PM
Reply to: Message 654 by Coyote
05-27-2015 10:49 PM


Re: Fossil Dating
That area of Africa had a lot of volcanic activity, so there are ash and other volcanic layers all over the place.
That reminds me of the KBS Tuff, beloved of creationists because originally two very different dates were obtained, therefore radiometric dating doesn't work. Of course it's really a triumph of the scientific method; the differences were argued out in Nature (arguably he most prestigious scientific journal) rather than being buried (as YECs claim discordant dates are treated). Only when the reason for the discordant dates was well understood,and multiple labs had replicated the final analysis using both Ar-AR and fission tracks, was the question settled.
Anyhoo, all the original samples were used up in the first measurements and the first attempt at replication in a different lab, so we'll never know exactly what went wrong initially. The original investigators' theory, published in the late 80's, is that the field workers, not trained geologists who collected the samples somewhat removed from the place where it overlays hominid fossils, got the wrong tuff because there are so many around there.

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Minnemooseus
Inactive Member


(1)
Message 658 of 1053 (758593)
05-28-2015 9:04 PM
Reply to: Message 657 by JonF
05-28-2015 1:40 PM


KBS Tuff
What offhand seems to be the best KBS Tuff topic is starting at message 7 of the "Dating Methodology and its Associated Assumptions" topic.
Moose

This message is a reply to:
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rick
Junior Member (Idle past 3337 days)
Posts: 2
Joined: 03-04-2012


Message 659 of 1053 (758611)
05-29-2015 3:05 PM


A new book "Beyond Intelligent Design: From an autonomous universe to a functional virtual reality:"argues that ID should be included in education in the context of a new concept called intelligent interaction:
http://www.amazon.com/...functional/dp/1511400625/ref=sr_1_3

  
ThinAirDesigns
Member (Idle past 2485 days)
Posts: 564
Joined: 02-12-2015


Message 660 of 1053 (758623)
05-29-2015 6:16 PM


Looking for Libby paper
Does anyone have a copy of the 1946 paper by Willard Libby titled "atmospheric helium three and radiocarbon from cosmic radiation"
It apparently is the first work on the C14 topic published by Libby. All I find is paywall.
BTW, though I don't like throwing money around I'm not broke - is there any one of these paywall sites that has access to enough of the sorts of earth science material I read that would be worth my money? I always appreciate the fact that you all are so willing to help, but I don't want to be a beggar.
Advice appreciated.
Thanks again
JB

Replies to this message:
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