Large bodies of water are a major feature of the Earth's surface. OCEANS, which are the largest bodies of water, are made up of saltwater and cover approximately 70% of the Earth's surface. Seas are smaller than OCEANS and are usually partially enclosed by land. They are also made up of saltwater. GULFS are even smaller than seas and are usually located within an ocean or sea. They are typically partially enclosed by land and are made up of saltwater.