#if 0
TMP=$(mktemp -d);
c++ -std=c++11 -o ${TMP}/a.out ${0} && ${TMP}/a.out ${@:1}; RV=${?};
rm -rf ${TMP};
exit ${RV};
#endif
#include <iostream>
int main()
{
std::cout << "Hello, world!\n";
}
(the trailing semi-colons in the script part is to make my editor indent the C++ code properly)
As for lichen growth, I couldn't differentiate the growth inside the carvings from that around them, so to 10-year-old me the carvings certainly appeared old.
But as an adult, I'd guesstimate that in that area, only ~100 years of lichen growth is enough for carvings to blend into the surrounding rock.
Edit: I am not sure if an lichen study was conducted.