Final answer:
Lucretius taught the Greek concept that atoms are indivisible and indestructible, based on the ideas of philosophers like Democritus and Leucippus.
Step-by-step explanation:
Lucretius, following the teachings of earlier Greek philosophers like Leucippus and Democritus, taught that atoms are indivisible and indestructible. This idea comes from the ancient Greek concept of 'atomos,' which means uncuttable or that which cannot be divided. While we now understand that atoms can indeed be split into smaller particles like protons, neutrons, and electrons, the Greek concept was one of the earliest steps towards our current understanding of the atomic theory. They correctly believed that atoms were the smallest unit that makes up matter, and that they were in constant motion.