Like everything else "your mileage may vary". Thinking about Mississippi, where some relatives are buried. Modern history there only goes back to the US Civil War, in ~1865. There is a lot of rain in Mississippi. A few people lived along the coast and up the river 300 years ago, but my relatives lived ~100 miles inland.
After 20 years or so, a piece of marble (CaCO3) will have a coating of crystals, like granulated sugar. The inscriptions will lose their sharp edges. Eventually the inscriptions are rounded indentations, barely legible. After a few more decades, they cannot be read. Perhaps the marble can last 80 or 100 years. I am not certain what the failure mode is for granite. It becomes covered with lichens in Mississippi. Basalt is an even harder stone than Granite, of course.
After writing that, I realized that there are things in Egypt which are still there from 4000-5000 years ago. But it does not rain frequently in Egypt.<\/div><\/div>
<\/div>","width":640,"height":426}
After 20 years or so, a piece of marble (CaCO3) will have a coating of crystals, like granulated sugar. The inscriptions will lose their sharp edges. Eventually the inscriptions are rounded indentations, barely legible. After a few more decades, they cannot be read. Perhaps the marble can last 80 or 100 years. I am not certain what the failure mode is for granite. It becomes covered with lichens in Mississippi. Basalt is an even harder stone than Granite, of course.
After writing that, I realized that there are things in Egypt which are still there from 4000-5000 years ago. But it does not rain frequently in Egypt.<\/div><\/div>
<\/div>","width":640,"height":426}