Indentured servants and chattel slaves were quite different, both in practice and in law. Chattel slaves were slaves for life and their offspring became slaves for life. There was no escape unless they were freed by their owners.
Indenture servants were released from their contract at a period of time stipulated in the contract. In most colonies they received a piece of land and farm implements when they released from their indenture. Their children were not bound under the indenture. The most common form of indenture came from the debt that was owed to a ship owner whom had provided passage to the New World. The ship captain would sell the indenture to planters who needed laborers. When those servants had worked off their debt, they became free.
I believe black slavery began in the 1500s. English Captain John Hawkins would take ships to Africa, buy captured blacks from the local chiefs, (those not bought were eaten by the local blacks).
Hawkins then took his ships to South America where he sold slaves around the Caribbean until his fleet was captured and sunk by the Spanish at Vera Cruz.
Hawkins escaped to later fight against the Armada. His slaves, captured by the Spanish, were sold to profit Spain.