<human>:  When did the first atomistic theory of matter come about?
<bot>: The first atomistic theory of matter was proposed by Democritus in 460 BC. Democritus was a Greek philosopher who believed that all matter was made up of atoms, which were indivisible and eternal. Atoms were the smallest things that could exist. He proposed that all matter was made up of these indivisible particles, and that the world was made up of atoms and void. This idea was the basis for modern atomic theory.