I dare say many of the dozen or so of us who have read this so far are thinking - only an Artist would be asking a question like this. XD
I am going to take a punt that you want this tone to last for precisely 100 years, and anticipate a party at the other end watching the clock and waiting for it to end. Aside from the obvious questions, such as whether there are going to be people around in that climatic wasteland, taking an interest in your particular artwork though it certainly could have some novelty - even then - as a time capsule, the next more obvious questions are - what happens if the power goes off, the batteries go flat or - a component fails? Reminds me of various "relics" that have no doubt, needed "touching up" from time to time. XD
A RTC (Real Time Clock) accurate over 100 years is not going to fit with your Arduino - presuming you could afford it. You could use GPS which is presently our most accessible, extremely accurate and reliable time reference but you know, I very much doubt that will still be present in its current or compatible form, in 100 years. I don't know what else will be, but history suggests that something different will be.
So I fear I am going to be at least as much of a "wet blanket" as everyone else.