Islands are landmasses smaller than continents that are completely surrounded by water, ranging from tiny coral cays to vast expanses like Greenland. They form through various geological processes—such as tectonic movement separating land from continents, oceanic volcanic eruptions building up layers of lava, or coral reefs accumulating over time. Because of their natural isolation, islands often harbor unique ecosystems with species found nowhere else on Earth, making them critical hotspots for biodiversity while serving as home to distinct human cultures and island nations worldwide.