Methods of dating

[Illuminatus]

I thought that I'd post on some of the lesser-known methods of dating materials. YECs, feel free to try to refute all of the methods that can date older than 6000 years. (Except for dad. We've all heard his stuff already.)

Uranium series
Range: approx. 10,000 to 800,000 years ago
Two isotopes of uranium (238 and 235) decay into other elements. In the case of U238, thorium 230, and for U235, protactinium 231. Of course, Th230 and Pa231 also decay. However, the uranium isotopes are soluble in water, while Th230 and Pa231 are not. For example, only the uranium isotopes are present in water that seeps into limestone case. However, once the calcium carbonate and uranium is precipitated onto the cave walls (known as travertine), the radioactive clock starts. When the travertine deposits are formed, they contain only the uranium isotopes and not the thorium or protactinium. Once the uranium is precipitated, though, the thorium and protactinium created through decay remains in the travertine deposits, and we can date the deposits based on our knowledge of the half-lives of uranium, thorium, and protactinium. Also, teeth can be dated using this method, as uranium "soaks" into the dentine coating of teeth after they are buried. This method has been used to date Neanderthal skeletons found in Israeli caves to approximately 100,000 years ago.

Fission track
Range: approx. 100,000 years ago and older
Fission track is based on the spontaneous fission of uranium 238, found in a large variety of rocks, minerals, glassy meteorites, and volcanic glass. U238 naturally decays, eventually to lead, but it also occasionally divides in half, with each half of the atom moving away at a very high speed, doing damage to the glass. The volcanic glass is polished and etched with acid, causing small fission tracks to become visible at high magnifications. As we know the rate of fission of U238, by counting the number of fission tracks and comparing them with artificially induced fission tracks of U235, scientists can determine the age of a material. Assuming the material is old enough, (around 100,000 years, old enough for a good quantity of tracks), the material can be dated to within +/- 10 percent.

Thermoluminescence and optical dating
Range: present to 100,000 years ago
This one is more difficult to explain without resorting to quite a bit of physics, but I'll try to keep it fairly simple. When atoms located within a crystal lattice, (basically, minerals), are exposed to nuclear radiation, (such as naturally-occuring cosmic radiation), single electroncs can and do absorb energy, become detached from their nuclei, and "trapped" within defects in the lattice (caused by missing atoms or impurities). As the amount of radiation absorbed remains relatively constant, the number of trapped electrons will gradually grow at a constant rate. By this, we can determine the total dose of radiation absorbed. By dividing the total dose by the annual dose, we can get an approximate age of the material.
Thermoluminescence dating is one method of emptying the "electron traps" by the application of heat. The material is rapidly heated to at least 500 degrees C, and energy lost by electrons as they are liberated from the traps is released as light, and known as thermoluminescence. The magnitude of the thermoluminescence is directly related to the number of trapped electrons.
Optical dating instead relies upon electron traps that are emptied by light. Most minerals have a set of electron traps that are "bleached" by several minutes exposure to sunlight. After burial, they begin to accumulate electrons again. Instead of heating the material to determine the number of electrons, it is instead illuminated and the electron luminescence is measured.

I'm taking a quick break, and I'll post the other methods in a bit.

 

[Illuminatus]

Electron spin resonance
Range: 5,000 to 2,000,000 years ago
ESR is most often used for the dating of teeth, due to the presence of a particular mineral in the enamel called hydroxyapatite. When hydroxyapatite is formed, it contains no trapped electrons, but they begin to accumulate when the tooth is buried and is exposed to natural radiation. Note that ESR can be used with many minerals, but scientists have had the most success with enamel dating. The material to be dated is exposed to microwaves in the presence of a strong magnetic field. The field strength is varied, and as it is, the trapped electrons in the sample absorb microwaves of different frequencies and resonate. The magnitude of absorption is proportional to the population of trapped electrons, and therefore the total radiation dose can be calculated. ESR is less accurate than thermoluminescence, but is more appropriate for materials that are damaged by heat. ESR is accurate to within 10-20%, depending on circumstances.
Obsidian hydration
Range: present to 100,000 years ago
This one's simple and kinda cool. When obsidian (volcanic glass) is fractured, (like if it was being knapped to make an arrowhead), it begins absorbing water from its surroundings. The water forms a "hydration layer", with a thickness that can be measured under an optical microscope. One of the problems with this is that absorption rates and water levels are not standard across the planet, and therefore must be tested for set a standard for an area. Obsidian hydration is most accurate for a time period of about 10,000 years ago, but has been successful in dating artefacts from as far back as 120,000 years.Amino acid racemization
Range: 500 to 100,000 years ago
This method is used to date bone. The technique is based on the fact that all amino acids can exist in two mirror-image forms. These forms ("enantiomers") differ in their chemical structure. The form of an amino acid can be determined using polarized light, those that rotate the light to the left are L-enantiomers, and those that rotate it to the right are D-enantiomers. Living creatures only have L-enantiomers in their proteins, however, after death, these change at a constant rate (racemization) to D-enantiomers. This process is somewhat dependant upon temperature, and as such, using AAR in conjunction with another method to cross-date and calibrate makes it even more accurate.
Geomagnetic reversals
Range: 100,000 years ago and older
The earth's magnetic field is known to completely reverse itself every several hundred thousand years. Scientists have have determined approximately when these have happened, and based on the orientation of magnetic particles in pottery, (for example), we can determine the approximate magnitude and direction of the field at the time of their permanent "fixing".

 

[Illuminatus]

A couple sources I used for research:
Archaeology Theories, Methods, & Practices, by Renfrew and Bahn
Wikipedia (of course)
My own (ever brilliant) cerebrum

If anyone picks up any mistakes, please let me know. It's 5:30 AM, and I've been on a streak of insomnia for the past few days. My mind is going, I can feel it.

 

[madarab]

Great job, even though I was hoping the subject matter had to do with getting women to go out with you.

 

[Illuminatus]

Bump.

Ahem. I spend half an hour on a 1000 world post to educate you cretins, and I get one response? Bah. I'm converting to YECism out of spite.

 

[Loudmouth]

I have a question about the geomagnetic dating methodology. You claim that it can be used to date pottery by the strength AND direction of the poles within the pottery. I would think that only the strength can be used since the direction is set when the pot is fired in a kiln, not when it is buried.

 

[Illuminatus]

I have a question about the geomagnetic dating methodology. You claim that it can be used to date pottery by the strength AND direction of the poles within the pottery. I would think that only the strength can be used since the direction is set when the pot is fired in a kiln, not when it is buried.

You're right, and I should've been clearer on that. Actually, I should split that into archaeomagnetic dating and geomagnetic reversals, as they're two different methods.

Geomagnetic reversal dating is mainly used with minerals. Archaeomagnetic dating is used more recently, and primarily with pottery. When the pottery is heated, the iron particles in it permanently take up the magnitude and direction of the earth's magnetic field at the time of firing. Using this in conjunction with other methods of dating, scientists and archaeologists developed an excellent plot of the location of the orientation of the earth's magnetic field over the past 10,000 years or so, and this can be used to date pottery.

Thanks for catching that, Loudmouth.

 

[Loudmouth]

You're right, and I should've been clearer on that. Actually, I should split that into archaeomagnetic dating and geomagnetic reversals, as they're two different methods.

Geomagnetic reversal dating is mainly used with minerals. Archaeomagnetic dating is used more recently, and primarily with pottery. When the pottery is heated, the iron particles in it permanently take up the magnitude and direction of the earth's magnetic field at the time of firing. Using this in conjunction with other methods of dating, scientists and archaeologists developed an excellent plot of the location of the orientation of the earth's magnetic field over the past 10,000 years or so, and this can be used to date pottery.

Thanks for catching that, Loudmouth.

Okay, maybe I am not understanding something. The only time that the iron particles are free to move about and align themselves with the pole is when they are fired in a kiln. After they are fired they are removed, used, moved about, and then buried. The pottery found in the ground should not point to the archaic position of the pole, and if so only by chance. However, it will have the correct magnitude. If the pottery is reheated after burial, via geothermal mechanisms, then the pottery will realign to the magnetic field as it was during the geothermal event, not the magnetic field at the time when the pottery was orignally made.

I know that this technique is a viable technique, but it requires the material to remain motionless, or of known movement (sea floor), after solidification.

 

[Dr.GH]

Those are a good group of the less commonly encountered dating methods. One point to keep in mind regarding any method is that the field work needs to be properly done, and that this can often invalidate a particular date.

For example, thermoluminesence has some very rigid requirements in order to insure accuracy. I once fired an employee for smoking cigarettes around open excavation units (the third time I caught him doing it). Why waste money?

Mechanical and chemical surface alteration to obsidian is a serious problem. Post depositional movement is a thermo-remnant magnatism issue.

And so on.

Much of the creationist's "RATE" project seemed to specialize in making incorrect fieldwork choices, and then shouting about their "wrong answers." Very few real scientists like to brag about screwing up their basic methods. Creationists are different.

When done correctly, dating methods are very good.

 

[Dr.GH]

The two available dating methods for pottery are thermoluminesence, and electron spin resonance. On some samples, you can now try for a radiocarbon date.

Thermoremnant magnetism is not used on pottery. It is used on the floors of ceramic kilns, the floors of burnt buildings, and the soil just below a hearth.

One rather strange application I have used was from the oriented grains of magnatite when the iron-rich soil was deposited by water onto a prehistoric living surface. It did tell me when the site had been buried by slope wash.

 

[JohnR7]

I thought that I'd post on some of the lesser-known methods of dating materials.

I was expecting to learn some great pick up lines and some really worthwhile information about dating. But I got a feeling that the birds and the bees are not going to be so much a part of this conversation.

 

[Dr.GH]

I was expecting to learn some great pick up lines and some really worthwhile information about dating. But I got a feeling that the birds and the bees are not going to be so much a part of this conversation.

Christian dating is only done by the book.

 

[Illuminatus]

Thermoremnant magnetism is not used on pottery. It is used on the floors of ceramic kilns, the floors of burnt buildings, and the soil just below a hearth.

That's interesting. My archaeology textbook says otherwise, but I'll take your word over Renfrew and Bahn. It wouldn't be the first time I've seen them disagree with another Ph.D.

 

[Dr.GH]

I can not think of a single instance where TRM has been used on a ceramic. TLD, and ESR but not TRM. Your library might have a copy of

R. E. Taylor & Martin J. Aitken, Editors
1997 Chronometric Dating in Archaeology New York: Plenum Press.

Good book. Taylor is an expert in C14, and Aitken is the expert on TLD, but they have top people review all current methods.

 

[Illuminatus]

I can not think of a single instance where TRM has been used on a ceramic.

I'm actually at home for the weekend, but when I get back up to school, I'll try to get the reference.

TLD, and ESR but not TRM. Your library might have a copy of

R. E. Taylor & Martin J. Aitken, Editors
1997 Chronometric Dating in Archaeology New York: Plenum Press.

Good book. Taylor is an expert in C14, and Aitken is the expert on TLD, but they have top people review all current methods.

Thanks. I'm a physics major, but archaeology has piqued my interest enough that it'll probably end up as my minor.

 

[JohnR7]

Christian dating is only done by the book.

Thanks God we do not have to get into that here on this board. But there is a board around here somewhere that does deal with those issues. I wish they had a board that deals more directly with death, but I can not find one. Maybe I need to talk to Erwin to see about setting one up.

 

[Buho]

I've been lurking on this thread since Illuminatus posted it. As of right now I feel underqualified to take this discussion further.

Perhaps while I read up more on this subject, you can present your views to recent findings of accelerating radioactive decay, specifically nuclear decay revolving around U238 and 4He in ZrSiO4 (zircon). The RATE program seems to have found experimental evidence for rapid radioactive decay, shortening time estimates from millions of years to thousands. If this is the case, our view of the world's history may be much elongated than we think.

I did some searches on CF here and to my dismay found nothing on variable decay rates. I'm interested in hearing what other scientists say about the research done on this by RATE and ICR. Google searches bring up very little when I filter out "creation" and "genesis".

Illuminatus, I notice that of the methods you list, only fission track and geomagnetic reversals can be used to date things older than a few million years, and of the two, geomagnetic reversals rely on secondary information that must first be dated. As of right now, I know nothing more about fission track than what you've written. I've got a lot to learn!

Some final thoughts before I return with something (hopefully) useful. The posts in this thread don't deal with common criticisms with dating methods such as sample contamination/leaching, and initial quantities at "year zero," both which are assumed and both which can dramatically effect the calculated date of the sample.

I'll be back in a week or two as I research more. Posting now as a sort of bookmark.

 

[Illuminatus]

I can not think of a single instance where TRM has been used on a ceramic. TLD, and ESR but not TRM.

Okay, I took the time to look this up in my archaeology text. It talks about using TRM on baked clay structures, such as ovens and kilns, and another project that makes it possible to date some Chinese pottery. As always, the Ph.D trumps the undergrad.

 

[Illuminatus]

Perhaps while I read up more on this subject, you can present your views to recent findings of accelerating radioactive decay, specifically nuclear decay revolving around U238 and 4He in ZrSiO4 (zircon). The RATE program seems to have found experimental evidence for rapid radioactive decay, shortening time estimates from millions of years to thousands. If this is the case, our view of the world's history may be much elongated than we think.

I've heard nothing of this, at least that I remember. I will look this up when I have time, but I have midterms in both physics and linear algebra tomorrow, (as well as a digital electronics lab test), and I'm rather strapped for time at the moment.

Illuminatus, I notice that of the methods you list, only fission track and geomagnetic reversals can be used to date things older than a few million years, and of the two, geomagnetic reversals rely on secondary information that must first be dated. As of right now, I know nothing more about fission track than what you've written. I've got a lot to learn!

I left out a number of better-known dating methods such as radiocarbon, potassium-argon, and chlorine-36, as they've been debated ad nauseum.

Some final thoughts before I return with something (hopefully) useful. The posts in this thread don't deal with common criticisms with dating methods such as sample contamination/leaching, and initial quantities at "year zero," both which are assumed and both which can dramatically effect the calculated date of the sample.

Again, I'm a bit short on time right now, but there's quite a few qualified posters around here who can probably address those questions.

 

[Dr.GH]

Okay, I took the time to look this up in my archaeology text. It talks about using TRM on baked clay structures, such as ovens and kilns, and another project that makes it possible to date some Chinese pottery.

I don't have your text at hand. Could you do the favor of looking up the reference to the chinese pottery study and posting it here? (just the citation).

As always, the Ph.D trumps the undergrad.

Well, it isn't just a hobby for me, it is how I earn $$$.

A weird application of residual magnetic fields is dating the flow of water through soils rich in magnetite. I have not published it, and I don't know if anyone else has taken the time to write it up either.

It would make a good thesis or even disertation if combined with cross dating of flowstone, (for example).