Complex sentence: The Bronze Age arrived circa 1500 BCE when people in the region were turning copper into bronze, growing rice, and domesticating chickens and pigs; they were among the first people in the world to do so.
Split into simpler sentences: The Bronze Age arrived circa 1500 BCE when people in the region were turning copper into bronze, growing rice, and domesticating chickens and pigs. They were among the first people in the world to do so.