Darwinist
Out of context: Reply #349
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JazX - I just read this, is this accurate (oh geology expert dude):
Will Carbon-14 dating work on all artifacts?
No. There are a few categories of artifacts that cannot be dated using carbon-14.
First, carbon-14 cannot be used to date biological artifacts of organisms that did not get thier carbon dioxide from the air. This rules out carbon dating for most aquatic organisms, because they often obtain at least some of their carbon from dissolved carbonate rock. The age of the carbon in the rock is different from that of the carbon in the air and makes carbon dating data for those organisms inaccurate under the assumptions normally used for carbon dating. This restriction extends to animals that consume seafood in their diets, as well.
Carbon dating also cannot be used on artifacts over about 50,000 years old. These artifacts have gone through many carbon-14 half-lives and the amount of carbon-14 remaining in them is miniscule and very difficult to detect.
Carbon dating cannot be used on most fossils, not only because they are almost always too old, but also because they rarely contain the original carbon of the organism. Also, many fossils are contaminated with carbon from the environment during collection or preservation proceedures.
How do we know Carbon-14 dating is accurate?
Scientists check the accuracy of carbon dating by comparing carbon dating data to data from other dating methods. Other methods scientists use include counting rock layers and tree rings.
When scientists first began to compare carbon dating data to data from tree rings, they found carbon dating provided "too-young" estimates of artifact age. Scientists now realize that production of carbon-14 has not been constant over the last 10,000 years, but has changed as the radiation from the sun has changed. Carbon dates reported in the 1950s and 1960s should be questioned, because those studies were conducted before carbon dating was calibrated by comparision with other dating methods.
Nuclear tests, nuclear reactors and the use of nuclear weapons have also changed the composition of radioisotopes in the air over the last few decades. This human nuclear activity will make precise dating of fossils from our lifetime very difficult due to contamination of the normal radioisotope composition of the earth with addition artificially produced radioactive atoms.
How do scientists date older fossils?
Although the half-life of carbon-14 makes it unreliable for dating fossils over about 50,000 years old, there are other isotopes scientists use to date older artifacts. These isotopes have longer half-lives and so are found in greater abundance in older fossils.
Some of these other isotopes include:
* Potassium-40 found in your body at all times; half-life = 1.3 billion years
* Uranium-235; half-life = 704 million years
* Uranium-238; half-life = 4.5 billion years
* Thorium-232; half-life = 14 billion years
* Rubidium-87; half-life = 49 billion years