Bryson reading #1

Quote: "Atoms are so numerous and necessary that we easily overlook that they needn't actually exist at all. There is no law that requires the universe to fill itself with small particles of matter or to produce light and gravity and other physical properties on which our existence hinges."

Question: If they are so easily overlooked and sometimes seem pointless, why are there atoms?

Comment: I was curious when I saw this quote and I started thinking, if there is no law that says that atoms are required in everything (like ourselves or the planets) then why are there atoms. And who says that there are atoms in everything, if we haven't traveled to other planets how would scientist know that they are made up out of atoms?