Complex sentence: Alchemy was already well established before the rise of Islam, based on the belief that substances were made up of the four Aristotelian elements, fire, earth, air, and water in different proportions.
Split into simpler sentences: Alchemy was already well established before the rise of Islam. It was based on the belief that substances were made up of the four Aristotelian elements, fire, earth, air, and water in different proportions.