There have been plenty of arguments that have refuted Van Sertima's work. Bernard Ortiz de Montellano probably has done the most detailed work in that regard. This isn't the first time that I've written about the flaws in Van Sertima's work as well.

I'm also not sure why you are suggesting that Van Sertima's lifetime work was his argument about the pre-Columbian African presence in America as if he didn't produce other works. They Came Before Columbus happens to be his most famous work, but it doesn't represent his entire life's work. Your statement does prove my point that today Van Sertima is best known for They Came Before Columbus and that book forms the basis of this growing trend of people claiming to be Native American rather than African.