Answer:
Life on Earth evolved in oceans, while the land was not suitable for living due to lack of ozone and oxygen. With time, photosynthesis enriched our atmosphere with oxygen and the ozone layer was formed. This allowed the ocean-based life forms to evolve and venture onto land. From skeleton-less soft bodies, animals evolved lighter bodies with slim, strong legs to carry them against gravity. They had hard exoskeletons to protect them against weather elements such as rain,...
Step-by-step explanation: