Lucretius Book 1 verse 52
……….. For now I begin to make
My discourse on the lofty law of gods and heaven above,
And shall reveal the building blocks all things are fashioned of,
Nature’s prime particles, from which she nourishes and grows (all things)
All things, and into which once more she makes them decompose.
We term them in philosophy, according to our needs,
Matter, atoms, generative bodies, elements and seeds, (and)
And first-beginnings since it is from these that all proceeds.

I am using the Stallings translation in the Penguin Classics edition of 2007

So these early atomists had astounding ideas. Leucippus was the first to speak of atoms. He stated that all things were eternal and simply changed from one form to another. He also thought the universe was a vacuum – an incredible idea. What experience would he have had of vacuums? He thought worlds were produced by bodies falling into this vacuum and becoming entangled with each other. Democritus almost 100 years later also maintained that the vacuum and the atoms were how the universe began. Nothing was created out of nothing and atoms produced all the combinations that exist in the form of fire, water, air and earth. He also wrote an essay on cheerfulness. Being cheerful was the greatest good of all. Epicurus in 300BC developed these ideas. He did not believe in the gods – he was an agnostic – and thought the development of matter did not require any form of divine intervention. Furthermore he did not think we were unique but that there were lots of earth-like bodies scattered about the universe. His understanding was that the world would produce all sorts of odd combinations of atoms creating weird kinds of creatures but that only those suited to their environment would survive.