Aristotle thought, ‘The egg in the belly of its mother bird is soft but it becomes harder when it comes out and touches the air, so that it will be less painful for the mother.’ But the egg is covered with hard eggshell even from inside of its mom’s belly.
The eggshell is hard enough to bear the weight of the mother bird, but also soft enough for the young to break it to come out. The main component of the shell was calcium carbonate. When it is time for the eggshell to be formed, the mother bird searches for food made of calcium carbonate by her instinct. The fine pores (air holes), which spread over the eggshell, allow oxygen to go into the shell and discharge carbon dioxide for the embryo to breathe, preventing germs from passing in. Water is formed while the embryo is growing. Then the pores release vapor to protect the embryo from suffocating.
Likewise, eggshells look simple but in actuality, they are very sophisticated. Eggshells protect the embryos with the best function in various environments whether they live in cold, hot, humid, or dry regions or whether they are in a warm nest or exposed on rocky cliffs. Eggshells are a perfect cradle made in mother birds.