National Geographic - carbon 14 Dating

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National Geographic - carbon 14 Dating

Postby CarpeDente on January 14th, 2015, 5:58 pm 

Has anyone read the most recent National Geographic? The cover story is a very interesting article with special reference to first human archievements. Of particular interest is archelogical evidence of animal forms, human forms, etc. in art form.

On a related topic, Carbon-14 dating has been discussed on other my philosophical sites. I have given up trying to discuss this with non-scientists. It seems those who oppose science have taken it as an area of distrust and are attempting to refute the valdity. I have now begun research into other means of dating ( I hope my wife doesn't misread this). Rather, other means to establish the age of an aritifact. Any help would be appreciated.
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Re: National Geographic - Carbon 14 Dating

Postby Forest_Dump on January 15th, 2015, 7:37 am 

C14 is but one of the radiometric dating methods with others being Potassium-Argon, uranium, etc. Basically all look at the ratio of unstable radioactive isotopes compared to stable (decayed) daughter isotopes. The decay rates are constant but differ in how fast they decay with C14 being fast (measured by the half life) while the others are slower and therefore take longer to get to observable differences in the ratio. They may also be more difficult to find as you don't find volcanic ash everywhere.

C14 is pretty good as all organic life (especially plants) takes in carbon and thus can be measured. Problems crop up, however, in that there are changing ratios of unstable carbon in the atmosphere due to volcanos or even forest fires and some plants take in and store carbon during photosynthesis differently and so die with different ratios of stable and unstable carbon which appears to set the start time of their atomic clocks differently. Some ocean critters also are exposed to water that appears to be older and so some shells can throw you off if you are not careful (this has been studied a lot).

But there are many other ways of dating things. Rarely and recently, a date might be stamped on something like a coin or building, etc. Sometimes wood or charcoal is complete enough you can match up the pattern of tree rings like a bar code using the growth patterns that vary due to periods of cold weather or drought vs warmer and/or wetter times (dendrochronology). Then too you can C14 date wood of known age to help recalibrate C14 dates because of the changes in the ratios of stable vs unstable carbon in the atmosphere (it turns out that real dates from 10,000 years ago are a couple of thousand years older than the C14 dates would have you believe).

Of course a huge problem can be thinking about just what it is you are dating. Imagine you have a tree that lived 500 years before it died. The inside is 500 years older that the outside and would date that way. So, if someone burned that an archaeologist might only recover the charcoal from the inside and get a wrong date. Or perhaps it was burned in a forest fire and someone found charcoal another 500 years later and used it for pigment or paint. And so it goes. Even thousands or more years ago people collected fossils (or artifacts) not unlike we do.

There are other methods, of course, but the most common is the use of changes in styles of various things. I am sure you can spot changes in style in clothing or cars and tell how old that style is. But there were certainly antique collectors in the past and sometimes people did get retro. In other words, care is certainly always necessary.
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Re: National Geographic - carbon 14 Dating

Postby CarpeDente on January 17th, 2015, 11:21 am 

Thank you for an excellent lucid reply. I have researched the anti-science dismissal of C14 dating, in the same way climate change opponnets push to retain dogma. People either hold onto answers for comfort or they reach out for answers to move forward by means of science as the only method to obtain data which then becomes fact to formulate a system to obtain knowledge. Philosophy no longer promotes opening these doors.
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Re: National Geographic - carbon 14 Dating

Postby zetreque on January 17th, 2015, 12:48 pm 

Another dating method (though it only works if you have a naturally magnetic personality) is paleomagnetic dating.

When lava is in liquid form, it's iron aligns with the Earth's magnetic field, and then solidifies in that alignment. Earth's magnetic field has reversed multiple times in the past (the best example is the ocean floor as it spreads) as well as drifted. As long as your rock hasn't been moved by humans, you can look at the magnetic alignment of it's iron, and compare that to the surrounding samples around the world and multiple other techniques. Through this we can see continental drift and estimate ages.

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Re: National Geographic - carbon 14 Dating

Postby Eclogite on January 17th, 2015, 2:31 pm 

There is another interesting way in magnetism can be used to date archaeological sites: archaeomagnetic dating. This " is the study and interpretation of the signatures of the Earth's magnetic field at past times recorded in archaeological materials. These paleomagnetic signatures are fixed when ferromagnetic materials such as magnetite cool below the Curie point, freezing the magnetic moment of the material in the direction of the local magnetic field at that time." See here.

I believe thermoluminescence (TL) can also be used on ceramics (c), though I am more familiar with it in relation to dating the time of fall of meteorites by measurement of the TL of their crust. (The heat of entering the atmosphere resets the TL clock, just as firing a ceramic resets its clock.)

I'm sure there are other ingenious methods used by researchers.
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Re: National Geographic - carbon 14 Dating

Postby Forest_Dump on January 17th, 2015, 4:27 pm 

There are certainly plenty of dating methods, each with their strengths and weaknesses which often means applicability and precision and so all do require a great deal of care and that usually means training. Paleomagnetism could stand as an example as it can also be applied with even the most simple of fire places (hearths). The broad stroke variety simply can measure whether the north pole pointed north or south (i.e., polar reversals). But sometimes they can also measure the more sensitive migration of the poles such as has been happening more rapidly lately. While this kind of dating can be helpful in some contexts you need to think about how we might know when, for example, a polar reversal happened. (Answer: it was dated probably with potassium-argon dating of a lava flow.) Personally I look for multiple lines of independent and supporting evidence but nothing is perfect.

As to the latter, often the antiscience people remind me of someone who tries to fix computer problem with a hammer. When it doesn't work, would you conclude that either hammers are not good tools or that computers are unfixable? Probably neither I would hope. But some will try to argue both.
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