If you look it up then this will make sense: Events can be recorded by nature, in the very rocks on the ground. Sound waves can still be circulating. The NSA can and does "pull" cell phone conversations out of "the ether" in order to record them.
Marli
It sounds like a physics or engineering question, not a question regarding literature or popular fiction or learning the craft skill or writing a book.
Look up "Father Ernetti's Chronovisor" using an internet search engine.
If Father Ernetti and his Chronovisor are science fiction, you still should ask the scientists about the validity of the statement.
Sir Caustic
Oh, sure. I listen to rocks al the time, just like I imagine everyone else does. My favourite's granite! What's yours?