Question about carbon dating

This article discusses dating some human bones found in the ground in Florida. They were originally excavated in 1915 and there are plans to do more digging. About the already recovered bones, the article says:

I don’t understand why being in the ground would hamper carbon dating. I thought this stuff was always found in the ground. Can someone explain this?

My guess is that they have fossilised and the organic contents have been replaced with minerals and turned to stone.

The main mineral structure of bone is calcium phosphate. When bones are buried, the organic materials in them can be dissolved away and replaced by minerals in the process of petrification or permineralization. Carbon dating of course can only be done if the bone retains its original carbon.

Nope. Not in only 100 years. Takes milliions and millions.

Nope. 5-10 years is sufficient in the ideal circumstances (cite)

Of course, it’s also possible that all of the organic content simply decayed away. Once bacteria and such get in there, you can’t trust the age of the carbon that’s left to be representative of the original artifact’s age. Water would be relevant to this only as far as it helps support decay.

Incorrect. Did you read the article linked to in the OP? The bones have been in the ground for at least 11,000 years, which is sufficient time for mineralization to have taken place. It certainly does not require “millions and millions.”

While mineralization/fossilization can take a long time (often thousands of years), under some conditions it can happen rapidly. From here (pdf):

The article in question also seems to imply that they are fragments, collected 100 years ago, possibly handled improperly. It may not be that these fragments can’t be carbon dated, just that, for some reason or another, no one wants to. Carefully checking to find an uncontaminated, organic-rich fragment may just not be a sellable idea.