Freethought & Rationalism Archive

Valentine Pontifex · 02-10-2002, 09:42 AM

I have incorporated some more reader suggestions.

<a href="http://home.mmcable.com/harlequin/evol/quotes/quotes3.htm" target="_blank">http://home.mmcable.com/harlequin/evol/quotes/quotes3.htm</a>

The biggest change is that one reader suggested that I, in the "argument from authority" section emphasize that real scientific papers do only rarely quote people. I will ask the science professionals on this board to look at that section and see if you agree with my characterization of who scientists cite each other in journals.

ps418 · 02-10-2002, 10:15 AM

Quote:

Originally posted by John Solum:

Sometimes it can. If the fossils occur in a shale, it's possible date the clays (specifically the clay mineral illite) that form during diagenesis, which would give you the time of deposition of that sedimentary rock. This is a minor point, but I thought I'd point it out. It's not widely done, but it is possible.

Same thing with glauconite (and barite too, IIRC), which forms syndepositionally. There are also some evaporite minerals that can be dated this way, but they are easily altered by later diagenesis.

Dr.GH · 02-10-2002, 10:59 AM

L.V.

You a quite correct about the fairly rare use of quotation in scientific journals. It is somewhat more common in texts, more in the social sciences than in the physical. Gary

John Solum · 02-11-2002, 06:32 AM

Quote:

Same thing with glauconite (and barite too, IIRC), which forms syndepositionally. There are also some evaporite minerals that can be dated this way, but they are easily altered by later diagenesis.

Glauconite's a good one, I haven't heard of anything being done with barite though. What evaporite minerals are you thinking of?

Coragyps · 02-11-2002, 07:31 AM

Hmm. I'd think barite would be excellent for dating, with strontium and radium both coprecipitating with the barium. That way you would have Sr-Rb for the long term, and Ra-Pb for younger samples. And, at least in oil wells, the barite you usually see is very dense and crystalline, and might resist alteration well.

Dr.GH · 02-11-2002, 08:03 AM

"Uranium Series Dating" by Henery P. Schwarcz in
Chronometric Dating in Archaeology Taylor and Aitken ed.s, 1997 New York: Plenum Press.

Traverine, marl, calcrete, and speleothms are all potential materails that may be directly associated with artifacts, or bone. Calcite deposited in the marrow cavities of bone can also be productive.

message icons can make punctuation difficult

[ February 11, 2002: Message edited by: Dr.GH ]

John Solum · 02-11-2002, 08:35 AM

Coragyps:

Quote:

Hmm. I'd think barite would be excellent for dating, with strontium and radium both coprecipitating with the barium. That way you would have Sr-Rb for the long term, and Ra-Pb for younger samples. And, at least in oil wells, the barite you usually see is very dense and crystalline, and might resist alteration well.

I haven't heard of that before (but that certainly doesn't mean it doesn't exist). I did a quick search of the literature and I could only find a couple of papers on it. Have you used this technique?

Dr.GH

Quote:

"Uranium Series Dating" by Henery P. Schwarcz in
Chronometric Dating in Archaeology Taylor and Aitken ed.s, 1997 New York: Plenum Press.

Traverine, marl, calcrete, and speleothms are all potential materails that may be directly associated with artifacts, or bone. Calcite deposited in the marrow cavities of bone can also be productive.

I think uranium series dating is an interesting technique, but it's only good back to either 300 ka or 500 ka (depending on who you listen to), so it has limited applicability. The guy who taught me geochemistry as an undergrad had used it to date speleothem calcite.

Coragyps · 02-11-2002, 10:13 AM

Quote:

I haven't heard of that before (but that certainly doesn't mean it doesn't exist). I did a quick search of the literature and I could only find a couple of papers on it. Have you used this technique?

No, I've never been involved in real geology, just in ripping all the petroleum I could get from Ma Earth's womb. But the idea sounds feasible, if naturally precipitated barite behaves properly with respect to diagenisis.

ps418 · 02-11-2002, 01:17 PM

Quote:

Originally posted by John Solum:


Glauconite's a good one, I haven't heard of anything being done with barite though. What evaporite minerals are you thinking of?

One example is langbeinite. Renne et al. (2001) have a paper describing 40Ar/39Ar analyses of this mineral from the Permian Salado Formation.

Renne et al., 2001. 40Ar/39Ar dating of Late Permian evaporites, southeastern New Mexico, USA. Earth and Planetary Science Letters 193, pp. 539-547.

Patrick

Dr.GH · 02-11-2002, 02:49 PM

Improved instrumentation has extended the time zone for U series dating upward to just a few centuries, and reduced the required sample sizes. The sample size reduction has the interesting consequence of reducing contaminants by alowing greater selectivity.

One can use either quadrapole mass spec. or accelerator mass spec.

02-11-2002, 08:03 AM	#16
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	"Uranium Series Dating" by Henery P. Schwarcz in Chronometric Dating in Archaeology Taylor and Aitken ed.s, 1997 New York: Plenum Press. Traverine, marl, calcrete, and speleothms are all potential materails that may be directly associated with artifacts, or bone. Calcite deposited in the marrow cavities of bone can also be productive. message icons can make punctuation difficult [ February 11, 2002: Message edited by: Dr.GH ]</p>

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02-10-2002, 09:42 AM	#11
Valentine Pontifex Veteran Member Join Date: Jul 2001 Location: Orion Arm of the Milky Way Galaxy Posts: 3,092	I have incorporated some more reader suggestions. <a href="http://home.mmcable.com/harlequin/evol/quotes/quotes3.htm" target="_blank">http://home.mmcable.com/harlequin/evol/quotes/quotes3.htm</a> The biggest change is that one reader suggested that I, in the "argument from authority" section emphasize that real scientific papers do only rarely quote people. I will ask the science professionals on this board to look at that section and see if you agree with my characterization of who scientists cite each other in journals.

02-10-2002, 10:59 AM	#13
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	L.V. You a quite correct about the fairly rare use of quotation in scientific journals. It is somewhat more common in texts, more in the social sciences than in the physical. Gary

02-11-2002, 07:31 AM	#15
Coragyps Veteran Join Date: Aug 2001 Location: Snyder,Texas,USA Posts: 4,411	Hmm. I'd think barite would be excellent for dating, with strontium and radium both coprecipitating with the barium. That way you would have Sr-Rb for the long term, and Ra-Pb for younger samples. And, at least in oil wells, the barite you usually see is very dense and crystalline, and might resist alteration well.

02-11-2002, 02:49 PM	#20
Dr.GH Veteran Member Join Date: Jul 2001 Location: Dana Point, Ca, USA Posts: 2,115	Improved instrumentation has extended the time zone for U series dating upward to just a few centuries, and reduced the required sample sizes. The sample size reduction has the interesting consequence of reducing contaminants by alowing greater selectivity. One can use either quadrapole mass spec. or accelerator mass spec.

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