The s in island is a spelling mistake from the fifteenth century
English speakers once wrote iland, from an Old English word distantly related to Latin aqua, water. In the 1400s writers wrongly linked it to the French isle and slipped in a silent s. Islands themselves are just as surprising, from sunken continents to evolutionary laboratories.
An island is land surrounded by water that is not a continent, and no size threshold separates the two; geologists define a continent as the largest landmass on its tectonic plate. Continental islands broke away from a mainland through plate movement. Japan may have been pushed off Eurasia by seafloor spreading, while New Zealand is a remnant of Zealandia, a mostly drowned continent-like block. Oceanic islands were never attached to a continent: many rise from volcanic hotspots, and as a plate slides over a fixed hotspot it leaves a chain of islands, older and more eroded the farther they lie from the source.
Other islands build themselves. Coral reefs growing around a sunken volcano can form a ring-shaped atoll around a lagoon. Waves pile sand into long barrier islands that absorb storm energy before it reaches the coast. Rivers deposit fluvial islands, usually low and temporary, though some are permanent; the largest fully inland one is Bananal Island in Brazil, up to 55 kilometres wide.
Isolation makes islands natural experiments in evolution. Only organisms able to fly, swim, hitch a ride or float across on debris reach oceanic islands; tortoises, which can go weeks without food or water, are good rafters. Arrivals often face little competition and split rapidly into new forms, a process called adaptive radiation. Darwin's finches on the Galápagos, up to fifteen species with beaks suited to seeds, cactus or insects, are the classic case. Island ecosystems have the highest rates of endemism anywhere, which makes them conservation priorities. Freshwater fish on an ocean island are a clue that it was once part of a continent.
People have lived on and sailed between islands for thousands of years, and up to 10 percent of humanity lives on them today. European colonisation brought most Pacific islands under foreign rule. Now rising seas threaten to submerge entire nations, including the Maldives, the Marshall Islands and Tuvalu.
Source: Island
