As the title says I want to know how many generations of slaves could have lived as slaves in the US. From what point was it possible for a slave to have children? Could a slave alive at the time of abolition have been a descendent of some of the first slaves to arrive in the Americas? If not when was it likely that their first ancestors arrived in the americas?
The first slaves to be sold in America are thought to be the 20 slaves that were sold in Jamestown, Virginia, from a Portuguese ship in 1619.
Whether any of these slaves had slave children is unclear. In 1625, there were said to be only 25 Africans living in Virginia, though by 1660 the number had grown to 950.
http://afroamhistory.about.com/od/slavery/a/The-Start-Of-Slavery-In-North-America.htm
In 1808, the slave trade (importation of slaves) was prohibited, so, after that (other than a small number of smuggled slaves) increases in the slave population came from slaves born in the US.
Slavery was abolished in 1865, with the 13th amendment.
If we guess that the first slave child born in America to have later descendants might have been born in say, 1625? If we count a generation as 25 years, then a slave alive in 1865 might have been the 10th generation of slaves born in America. If we used 20 years to a generation, it might have been 12 generations.