Islands can be placed into two broad categories: oceanic and continental.  They come in countless shapes and sizes, from jagged and harsh to smooth and tropical. They also support a bizarre and amazing set of animals, such as the giant tortoises of Galapagos, Madagascar's agile lemurs, and the massive Komodo dragons. 

Oceanic islands, like the beautiful Hawaiian chain, were created by the oozing of hot lava from the tips of enormous underwater volcanoes.  Continental islands, such as California's Channel Islands, were once part of a larger land mass in recent geologic history, and have become separated from the mainland because of earthquakes or rising sea levels after massive glaciers melted years ago.