Very simply put, too many things are unknown to allow the carbon dating process to be as accurate as many proclaim it to be. Factors as diverse as changes in the earth’s magnetic field and changes in the amount of carbon available to organisms in times past could translate into perceivable differences in the carbon ratios in artifacts and remains from ancient times. Even changes in the atmosphere itself could impact this carbon ratio. We know that changes such as these have occurred over time. They are still occurring today in fact.
http://www.angelfire.com/mi/dinosaurs/carbondating.html
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Oh, I get it. "carbon data" = "carbon dating" = "radiocarbon dating".
"Radiocarbon dating, or carbon dating, is a radiometric dating method that uses the naturally occurring radioisotope carbon-14 (14C) to determine the age of carbonaceous materials up to about 58,000 to 62,000 years."The technique of radiocarbon dating was developed by Willard Libby and his colleagues at the University of Chicago in 1949... He first demonstrated the accuracy of radiocarbon dating by accurately estimating the age of wood from an ancient Egyptian royal barge for which the age was known from historical documents."
Carbon dating is only one of many methods, radiometric and others, used to estimate ages of ancient materials, including:
And these are far from the only methods of establishing ancient time lines. But, performed properly, they can be amongst the most consistent and reliable:
"Finally, correlation between different isotopic dating methods may be required to confirm the age of a sample. For example, a study of the Amitsoq gneisses from western Greenland used five different radiometric dating methods to examine twelve samples and achieved agreement to within 30 Ma on an age of 3,640 Ma."
Obviously, any of these tests might be performed incorrectly, contaminants introduced, external factors improperly accounted for, etc. But there is no scientific proof, none, which tells us these test are necessarily largely inaccurate, even if done correctly.