That egg must've had a very strong shell. Most supermarket eggs we buy have very thin fragile shells. I used to buy fresh eggs from a city chicken farmer believe it or not. They would be different sizes and colors. I had to rinse them as well, they had dirt and poop. Every once in a while I'd get an egg that was very difficult to crack and had a very thick strong shell. Don't think it'd hold up for 1000 years though.