Complex sentence: The Age of Discovery, also known as the Age of Exploration, was a period starting in the early 15th century and continuing to the 17th century during which Europeans explored Africa, the Americas, Asia and Oceania.
Split into simpler sentences: The Age of Discovery (also known as the Age of Exploration) was a period starting in the early 15th century and continuing to the 17th century. During this period Europeans explored Africa, the Americas, Asia and Oceania.