It is the largest island in the world, but it is also the smallest continent in the world. What is the usage of the world?

Noun possessive case, noun possessive case is used to indicate inanimate besides animate. Such as country, city, celestial body, collective noun, time, etc. , and then add s to indicate something. The earth's surface, China's policies, China's policies, today's weather, today's weather, and so on.