The discovery of the electron disproved the idea that atoms were tiny indivisible spheres. Before this discovery, atoms were thought to be the smallest, indivisible particles of matter. J.J. Thomson's experiments in 1897 showed that atoms contain much smaller negatively charged particles called electrons. This meant atoms were not indivisible but composed of smaller subatomic particles. Thomson proposed the "plum pudding" model, in which electrons were embedded within a positively charged sphere, challenging the notion of solid, indivisible atoms. Thus, the electron's discovery disproved the idea that atoms were tiny, indivisible spheres.