[emiliobumachar]

I guess if the Great Barrier Reef starts recovering, we could etch some dire warning into the rock about to be covered by life, to be seen the next time things get this bad.

"If you see me, you will weep. So barren was our ocean in 2018."

If only, the Reef is likely irreversibly dying by now.

Any other applications?

[adrianN]

Areas that used to be covered by glaciers.

[jtbayly]

Seems like in front of a glacier's path when it's about to start growing is a bad place to put something that you want to survive for future generations to read.

[adrianN]

You'd have to carve it fairly deep into the rock.

[jtbayly]

Also, you'd have to anchor it really well if you didn't want it to move with the front of the glacier and reappear the first summer the glacier retreated by a couple of feet, instead of when the glacier shrunk to disastrously small.