I looked all over for a date and got everything from “early 1800s” to “late 1800s” but nothing exact, so I had to make an educated guess. The first cameras practical enough to take such a photo were developed around 1840 and the excavations began in 1867.
I kinda like it better since it makes the same criticism of people who think their works will last forever, but then goes a step further and exposes the same fallacy in modern peoples.