Democritus of Abdera (c. 460-370 BC) was a Greek philosopher and early proponent of atomic theory. He proposed that matter was made of discrete indivisible particles, after contemplating an observation made by a teacher that a beach looks smooth from afar, but is really made of discrete grains of sand. He called his particles atomos, meaning "cannot be cut." He believed these particles to be eternal, indestructible, and unchanging. Democritus helped resolve the question of how a world evidently in a state of flux could be founded upon an underlying nature that was eternal and unchanging; however, his ideas were largely ignored until the scientific revolution leading from the Renaissance. He also pursued studies in physics, astronomy, zoology, botany, and medicine. In an impressive observation for his time, Democritus maintained that the Milky Way galaxy was a conglomeration of stars.