why is carbon dating useless after ~ 50,000 years?

Answer 1

because there isnt enough to measure

carbon dating is measuring a low raioactive carbon 14 that decays. for different substances, half will 'decay' over a certain amount of time. carbon 14 has a 'halflife' of about 5000 years. so if scientists can figure out how much was there before, they can measure how much is there now, and make a judgement as to how old it is. say for example there is 5 g of C14 in a bone, and scientists believe that it had 20 g when the organism died (with no new C14 entering the body) scientists would estimate that the bone was 10,000 years old, 10/2 =10g /2 = 5g

after 50,000 years, there is only 1/1000 C14 left, and measurements beyond that, or any other radioactive substance beyond 10 half lifes, are unreliable, and hard to measure

Answer 2

Carbon dating is a wonderful dating technique... when used on the proper types of samples and with the understanding that it does have this ~50, 000 year limit. As another responder points out, with only 1/1000 of the original C-14 left after a few half-lives, experimentally accurate measurements become unlikely. Remember, there wasn't much C-14 to begin with!

Also note that not everything can be carbon dated---like rocks for example, or items taken from the ocean. Only terrestrial, once-living things are really suitable fo C-dating. Marine items are not C-dated because they draw their C from the oceans, and C-dating assumes that you're looking at things that had the atmosphere as the C reservoir.

Take a look at the USGS web site that explains carbon dating for a complete treatment of the whats and whys involved.

Good Luck

Answer 3

Carbon dating is based on finding the proportion of a radioactive isotope of carbon in standard carbon.

What happens is plant and animal life all thrive off of carbon, some of which becomes radioactive after solar rays (xrays, gamma rays, really fast ions) hit atmospheric carbon and transform it into a radioactive isotope.

As soon as that plant or animal dies, it stops changing its isotope to normal carbon ratio. Then the isotope carbon slowly begins to decay. This means we have a slowly decaying fingerprint of when that organism was alive.

The reason it won't work for stuff well into the past is because the isotope that decays is essentially like the ridges of your fingerprints. As the ridges decay more and more, it's harder and harder to accurately see the pattern.

For carbon, the isotope decays to a very trace amount after ~50k years and cannot be reliable (except to say that something was older than 50k years).

Also, one neat thing is that with all the nuclear weapons testing we did during the cold war, the radioactive carbon content is all messed up now, and carbon dating in the future won't work so well when it comes to this time period.


INRE the earlier answers, carbon dating shouldn't be done on rocks anyway.

Answer 4

carbon dating is done by measuring the amount of carbon 14 it contains, i am not sure if 50,000 years is the exact figure, but the method is rendered useless because of the half life effect and will eventually reach a point where the amount of carbon left will not longer be enough for concrete substantiation.

Answer 5

it is all based on detecting the amount of radiation from carbon based matrial as it has a radioactive carbon compomnent , when that "thing " dies or get cut off supply of carbon , the radio active carbon inside decays at a steady rate , and it's half life is about 5000 years , after 50,000 the radiation would be too low to detect , so they wont be able ot tell how much carbon is left

Answer 6

Carbon-14, which is used to measure the age from when an organism died, has a half-life of 5760 years. you are talking about nine times that, meaning that the concentration would be 1/2 times itself nine times, roughly 1/500 of the original concentration. When you get to these smaller concentrations, the error inherent in the measurement increases the error range of the result by a significant margin. Also, it becomes harder to measure such small concentrations.

Hope that helps.

Answer 7

Carbon dating has proven to be useless time after time due to experiments on newly formed rock from volcanoes. Rocks that were only a decade old have been dated at several thousand to several million years old. It is a useless method.

Answer 8

Is it? I would guess that in a large enough sample it wouldn't be. But for small samples, there just isn't much of the radioactive carbon-13 left, so it gets very difficult to be precise about relative proportions.

Answer 9

Because the carbon-14 has already decayed.

Answer 10

well overall carbon dating isn't reliable..

just the longer the period the lesser elements are in the piece in question that the process can accuratly indicate.

that's all... things dry up.. when those things aren't present or guarenteed to be existant.. the process of the dating is.. well basically extinguished.