Answer: They were believed to be the root of all matter.
Explanation: Aristotle believed that all of the earth was composed of four elements: earth, air, fire, and water. Aristotle's proposed elements were considered "simple bodies" that only humans experience, each one having qualities of either hot or cold, and wet or dry. He also proposed a fifth element, Aether, which was considered the perfect element, beyond human understanding and fit for the gods. Overall, his proposed elements were considered to be the foundation of all matter, and everything was made of one of these four elements.