Conversation so far:
Who proposed that atoms are the basic units of matter
John Dalton proposed that each chemical element is composed of atoms of a single, unique type, and they can combine to form more complex structures called chemical compounds.

Question: how did the proposal come about
Self-contained rewrite: how did john dalton's proposal that each chemical element is composed of atoms of a single unique type, and they can combine to form more complex structures called chemical compounds come about