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An island is a relatively small area of land that is completely surrounded by water. It is impossible to give a total number to the islands that exist on the surface of the planet. As a result of erosion or rising sea level, some islands drown over time. The longest surviving islands usually last no more than 5 to 10 million years (Earth is 4.5 billion years old). Ongoing volcanic activity continues to create new islands and to add to existing ones. On November 14, 1963, a underwater volcanic explosion off the southern coast of Iceland created the island of Surtsey, which continues to gain land as the ongoing lava flows cool.

The eight largest islands on Earth are (in descending order): Greenland, New...