Answer:
To ensure that no drying of the embryo occurred.
Step-by-step explanation:
Because of the inhospitable environment, eggs from terrestrial animals that had a thinner shell were very susceptible to desiccation of the embryo. This made it difficult for the species to continue because it caused the embryo to die and did not allow a new being to be generated.
Over time, as a way of overcoming this disadvantage, some of the land animals had evolved to make thick-shelled eggs. The egg of these animals has a thick shell that prevented the drying of the embryo. However, the shell was porous, allowing gas exchange between the embryo and the external environment, thus ensuring the survival of the species.