How long did it take for ironworking to be commonplace in West Africa following its introduction in Northern Africa?

Context: By the first millennium BCE, ironworking had been introduced in Northern Africa. Around that time it also became established in parts of sub-Saharan Africa, either through independent invention there or diffusion from the north and vanished under unknown circumstances around 500 CE, having lasted approximately 2,000 years, and by 500 BCE, metalworking began to become commonplace in West Africa. Ironworking was fully established by roughly 500 BCE in many areas of East and West Africa, although other regions didn't begin ironworking until the early centuries CE. Copper objects from Egypt, North Africa, Nubia, and Ethiopia dating from around 500 BCE have been excavated in West Africa, suggesting that Trans-Saharan trade networks had been established by this date.

Answer: Ironworking was introduced in Northern Africa around the first millennium BCE and became commonplace in West Africa by 500 BCE. This means it took 500 years (1000-500) for ironworking to become common in West Africa following its introduction in Northern Africa.