Carbon Dating

Can someone explain to me how we can be sure that Carbon 14 dating is accurate?  Given that its a relatively new technique and that nobody has lived 1,000's of years to verify it over long periods of time.

I know it has to do withh decay rates...I guess what I am asking is how do we know for sure that those rates are constant past say, 1,000 years?

  First: Are you asking about carbon dating, which is a specific technique to date once-living things (that acquire their carbon through respiration)?

   Or radiometric dating, which is used (except for Carbon dating) to date non-organics?

   Are you asking about that specific technique, or decay-based dating techniques in general? Carbon dating is a little more involved and unusual than regular radiometric dating. 

   In general, however, we know decay rates are constant for several reasons. First off, we've measured the buggers in the lab, and nothing we can do seems to shift them at all. Also, we know the things which govern radioactive decay. And, for decay rates to change, means some rather fundamental constants in the universe have to shift too. Which means things like "Stars stop shining".

   But most importantly, we have multiple method agreement. Now, when you measure samples, you're using things called "half-lives", which is the length of time it takes for half the parent element to decay. By measuring ratios of parent to daughter, you can determine how old a sample is. However, no two isotopes (or elements) have the same half-life.

   If you date a sample with more than one method, and get agreement, the decay rates must be constant. You see, if decay rates had changed, you would have to know the exact way the rates had changed to get agreement. The fact that you consistantly get agreement indicates that decay rates are steady. Under the dating methods used now, had they not been steady, you'd never get agreement.

   Think of three jugs of water. Each looses water at a different rate (One loses half the contents of the jug per hour. One loses half per day. One loses half per 12 hours). Now, at some random point after the jugs had started leaking, you wander in and measure the amounts of water each has lost. You know the rates they lose water, you know how much is left in the jug, and you know how much has collected in the pans beneath them.

   It'd be an easy matter to work out how long they had been dripping, and each jug would yield the same answer.

   Now, assume that the jugs didn't drip at a constant rate. Is there anyway you could determine how long they had been dripping if you didn't know the way the rate changed?

   More importantly: What are the odds that all three jugs had their rates change in such a way as yield the same "answer" if you pretended the rates hadn't change?

   And bear in mind here that you couldn't just arbitrarily change the numbers. Change one rate, and the others change likewise.

 

    
  

Radiometic...thanks for clarifying.

C14 dates have been verified against dates obtained via other means, such as counting the layers in glacial ice cores or by counting the growth rings on very old trees.

The decay rate of an isotope is strictly a probabilistic process described by the principles of quantum mechanics. There are only two ways I know of that the decay rate could change over time:

1. Extreme temperature and radiation
2. Change in the fundamental constants of physics (speed of light, Planck's constant, etc.)

Our confidence in the constancy of radioactive decay is based on the fact that the conditions in #1 are impossible on the surface of the Earth and there is no evidence for #2.

 I added a bit up above.

 

I see the logic in knowing that the decay rates are constant, but I don't think that answers my question. I am asking about how we would know they are constant for 1,000 years or more, since we can't see agreement among multiple tests over that long of time.

Or did I misunderstand?

I joined this forum two days ago when I saw intelligent posts from persons such as you two. Those were lucid and informed answers and I applaud you. Have you two ever been to the forum at SPACE.com? You might enjoy it! 

http://uplink.space.com/2/OpenTopic?...mp;s=874094803

May I recommend Free Space as a good place to start. I post there regularly as llovingo. This is not a commercial, and not a blatant attempt to steal people away from this forum.

  Souljah: We date things that are billions of years old. Of course we see rates are constant over time. If I date a rock by three methods that consistantly gives me 4.5 billion years, then I've got excellent evidence that the decay rates were constant for the last 4.5 billion years (or else I'd have gotten numbers that didn't agree).

  Further, as I've noted, you can't really change decay rates. They're locked heavily into the way the universe works. You know the constants haven't changed, because the Sun still shines, and the stresses you'd have to place on them temperature and pressure wise would have turned everything to highly compressed ash.

 

It is possible to calculate the decay rates of certain isotopes by studying the remains of supernovas. The light from the supernovas have taken thousands of years to reach us, thus what were seeing is the actual decay rates thousands of years ago. And they appear to be exactly the same as they are today. This link goes into some more detail about it. It is meant as a reply to a common creationist claim that the speed of light might have decreased, but also mentions decay rates.

There are also independent ways to verify the ages obtained by radiomeric dating on the earth, e.g. from plate tectonics, the tilt of the axis of rotation of the earth and ice boring on Greenland to mention a few. If you want I'll try to dig up some more info on this.

Choccy

Radiometric dating has many potential problems, most of which have to do with the fact that we have to make assumptions about the amount of parent materials present at the time we assume the clock started ticking.

Also, decay rates do change under some conditions. Whether or not this actually has any affect on radiometric dating is questionable, but one cannot completely rule it out.

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