Dr. Hovind (R3): The initial C-14 content cannot be known. Different parts of the same sample often yield different ratios of C-14/C-12. Various living samples give very different ratios.With at least one notable exception on the books, plants and animals get their carbon-14 from the atmosphere. Plants take it in directly, and animals eat the plants. Thus, it gets passed up the food chain. It is not surprising, therefore, to find that the carbon-14 in living plants and animals is in reasonable equilibrium with the atmospheric carbon-14. Some creationists, however, have claimed that certain plants can reject carbon-14 in favor of carbon-12. Because of the chemical similarity of carbon-14 and carbon-12, it is unlikely that such plants could deviate much from the ratio of C-14 to C-12 found in the atmosphere. Neither freak cases nor small deviations pose much of a problem for radiocarbon dating, which, after all, draws upon a wide variety of plant and animal species. Hence, we only have to worry about the initial concentration of C-14 in the atmosphere. Topic R1 shows that the level of C-14 in the atmosphere has not varied appreciably over tens of thousands of years. Therefore, the initial C-14 content is known for any reasonable sample!
The notable exception involves certain mollusks, which get much of their carbon from dissolved limestone. Since limestone is very old it contains very little carbon-14. Thus, in getting some of their carbon from limestone, these mollusks "inherit" some of the limestone's old age! That is, the limestone carbon skews the normal ratio between C-12 and C-14 found in living things. No problem! If one dates such mollusks, one must be extra careful in interpreting the data. Not every mollusk shell presents such problems, and the dating of other material might yield a crosscheck. Further study might even allow correction tables. The discovery has strengthened the carbon-14 method, not weakened it! By the way, shouldn't the creationist be worried over the old, carbon-14 age of the limestone? Why is it that limestone has so little C-14 in it?
Different parts of the same sample may, indeed, yield different C-14/C-12 ratios. Partial contamination, say of a block of wood, may affect its different parts to different degrees. Insect burrows, cracks, and partial decay may allow contamination later on to affect those portions of the sample unequally. However, there are laboratory techniques, often ingenious, for dealing with such problems. If the sample shows evidence of being hopelessly contaminated it is pitched.
Some samples, such as a section of a tree trunk, may well contain material of considerably different ages. The interior portion of a tree trunk could easily be several hundred years older than the outer portions. Once again, the C-14/C-12 ratios would reflect this difference in age.
In summing up this point, we do know within good limits what the initial C-14 was for any reasonable sample. A sample will not have different ratios of carbon unless it has been contaminated or reflects a genuine range of ages.