According to chemical studies of the skeletons, especially the teeth, of Columbus’s crews, some members of the expedition may have been free black Africans who arrived in the New World 10 years before the slave trade began.
For example, the ratio of strontium isotopes indicates whether the person grew up in a region underlain by very old bedrock, such as West Africa, or newer rock, such as Latin America. That is because older rock has a higher ratio of strontium 87 to strontium 86.
Ratios of carbon isotopes in the teeth, meanwhile, reflect what foods a person ate. A diet heavy in corn, sorghum and other tropical plants yields more carbon 13, whereas grains such as barley and wheat produce more carbon 12. Europeans of Columbus’s time would have relatively little carbon 13 in their teeth; Mexicans would have much of the heavier isotope. Natives of Hispaniola and many Africans, who are believed to have eaten a mixed diet, would probably fall somewhere in between.