Carbon 14 dating summary
(Further, there is a pretreatment process of repeated washes of acid/alkali/acid to remove any outer humic acid and debris.) Therefore creationists have been correct to dispute Mary Schweitzer, Lindgren, et al., as they've tried to explain away as microbial contamination the "modern" carbon in an endogenous biomaterial Mosasaur bone. (See also this post from a committed evolutionist in a battle royale with our old friend rsr.org/david-willis at the forum run by RSR host Fred Williams.) Regarding Libby's "no known natural mechanism" way of contaminating collagen, here's our RSR explanation of why this is.
If a specimen is purified to 95% collagen, or 98%, or 99%, etc., then approximately the same percent of the carbon in the fossil sample will be endogenous (i.e., original to the living animal). Because new carbon atoms will not original carbon atoms in the collagen molecule.
Rather, the collagen must be manufactured within a living animal (with its constituent carbon atoms) into a "super-super-coil...
interdigitated with its neighboring microfibrils... so well ordered as to be crystalline." Further, bacteria do not make collagen, which eliminates another possible source of contamination.
Thus, where researchers find , "There is no known natural mechanism by which collagen may be altered to yield a false age." And as of 2019, there is still no known mechanism to contaminate collagen with modern carbon.As a result of decomposition, to the extent that original carbon atoms were falling out of the tissue (so to speak), then to that extent you would no longer have collagen; rather, to that extent you would have humic acid.