When animals crawled out onto the land they were suddenly seized by gravity. Gravity was not a major problem for them, and many eventually grew wings and learned to fly. Larger animals with internal skeletons had to adapt to gravity. This required stronger bones, muscles, hearts, and ligaments. These animals evolved from small ancestors, gradually developing bodies that could deal with gravitational stress.
Exoskeletons protect the body.
They are light and very strong, and provide attachment places for the muscles inside. They protect the body from dehydration, predators, and excessive sunlight. Exoskeletons lead to some difficulties, too. The shell does not grow, so it has to be shed periodically. It is a struggle to get out of an exoskeleton, and the animal is vulnerable while the soft new shell hardens, which may take several hours.