Carbon-14 cannot be used to date biological artifacts of organisms that did not get their 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.
Carbon dating is used to determine the age of biological artifacts up to 50,000 years old.
Although the half-life of some of them are more consistent with the evolutionary worldview of millions to billions of years, the assumptions used in radiometric dating put the results of all radiometric dating methods in doubt. 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.
Any radiometric dates that show a supposedly “old” rock to be young are rejected “Few people realize that the index fossil dating system, despite its poor assumptions and many problems, is actually the primary dating tool for geologic time. In other words, radiometric dating methods are actually fit into the geological column, which was set up by [index] fossil dating over 100 years ago.”(Michael Oard, meteorologist and creationist scientist, 1984) All radiometric dating methods use this basic principle to extrapolate the age of artifacts being tested.
These long time periods are computed by measuring the ratio of daughter to parent substance in a rock, and inferring an age based on this ratio.
Levels of carbon-14 become difficult to measure and compare after about 50,000 years (between 8 and 9 half lives; where 1% of the original carbon-14 would remain undecayed).
The question should be whether or not carbon-14 can be used to date any artifacts at all? There are a few categories of artifacts that can be dated using carbon-14; however, they cannot be more 50,000 years old.