The theory is not valid at all or popular among historians and archaeologists. This claim falls within the realm of pseudo-archaeology and fiction. Writers like Ivan Van Sertima cherry pick information to support their narrative. Claims like this are an extreme case of hyperdiffusion in which scholars try to link everything back to a single origin and do not take into account independent invention. There are two very good articles dealing with this very topic.

• Haslip-Viera, Gabriel, Bernard Ortiz de Montellano, and Warren Barbour. Robbing Native American Cultures: Van Sertima's Afrocentricity and the Olmecs. Current Anthropology 38(3): 419-441. 1997

• de Montellano, Bernard Ortiz, Gabriel Haslip-Viera, and Warren Barbour. They were not here before Columbus: Afrocentric Hyperdiffusionism in the 1990s. Ethnohistory. pp. 199-234. 1997.