The lime shell of a freshly laid egg is much thicker and stronger than the shell of an egg with

The lime shell of a freshly laid egg is much thicker and stronger than the shell of an egg with a nestling in it. What is the reason for this?

This is a rather controversial fact. The fact is that the embryo does not use the shell, does not absorb any elements from it, and so on. It is believed that the shell becomes less durable due to constant friction during incubation. For the chick, the thickness of the shell also does not play a big role, since the chick first punches a small hole and it will easily be released. Perhaps it degrades over time, under the influence of internal and external factors, but it is known that in incubators this effect is not as noticeable as during incubation.