Materialism isn’t the statement that the world consists of matter. This is obvious. It is the statement that any statement (including this one), thought, language, conscience, consciousness, moral, subject, personality is material. It is a not a thing in itself, but has to get the necessary attribute of meaning (sense); it has to exist in a material process over time in some substrate that can interpret it with other statements.
When the material substrate in which this takes place stops functioning, that particular statement, thought, … ceases to exist. Any statement, even 1+1=2, loses its meaning when there is no consciousness left that knows its meaning; when all the substrates that hold an adequate consciousness have stopped existing. Simply said: all humans who can make additions have died. It is possible that at some point in time, a new form of consciousness can come into existence that discovers addition, and maybe this consciousness will discover that in ancient times there was a civilization that could make additions.
Modern materialism was first described by Spinoza.