User:ForksForks/sandbox/Island



An island or isle is a piece of subcontinental land completely surrounded by water. There are continental islands, which were formed by being split from a continent by plate tectonics, and oceanic islands, which have never been part of a continent. Oceanic islands can be formed from volcanic activity, grow into atolls from coral reefs, and form from sediment along shorelines, creating barrier islands. River islands can also form from sediment and debris in rivers. Artificial islands are those made by humans, including small rocky outcroppings built out of lagoons and large-scale land reclamation projects used for development.

Islands are host to a diverse array of plant and animal life. Oceanic islands have the sea as a natural barrier to the introduction of new species, causing the species that do reach the island to evolve in isolation. Continental islands share animal and plant life with the continent they split from. Depending on how long ago the continental island formed, the life on that island may have diverged greatly from the mainland due to natural selection.

Humans have lived on and traveled between islands for thousands of years at a minimum. Some islands became host to humans due to a land bridge or a continental island splitting from the mainland. Polynesians were the first group of humans to colonize islands at scale, dispersing over the Pacific Ocean starting near New Guinea starting as early as 1100 BC. Today, up to 10% of the world's population lives on islands. Islands are popular targets for tourism due to their perceived natural beauty, isolation, and unique cultures.

Islands became the target of colonization by Europeans, resulting in the majority of islands in the Pacific being put under European control. Decolonization has resulted in some but not all island nations becoming self-governing, with lasting effects related to industrialization, nuclear weapons testing, invasive species, and tourism. Islands and island countries are threatened by climate change. Sea level rise threatens to submerge nations such as Tuvalu and the Marshall Islands completely. Increases in the frequency and intensity of tropical cyclones can cause widespread destruction of infrastructure and animal habitats. Species that live exclusively on islands are some of those most threatened by extinction.

Definition
An island is an area of land surrounded by water on all sides that is distinct from a continent. There is no standard of size that distinguishes islands and continents. Continents have an accepted geological definition -- they are the largest landmass of a particular tectonic plate. Therefore, if continents cannot also be islands, landmasses such as Australia are not islands. Australia is considered a continent because it sits on its own lithosphere and tectonic plate, the Australian Plate. Islands can occur in any body of water, including rivers, seas, and lakes. Low-tide elevations, areas of land that are not above the surface during a high tide, are generally not considered islands. Islands that have been bridged or otherwise joined to a mainland with land reclamation are soemtimes considered "de-islanded", but not in every case.

Formation in oceans
Islands often are found in archipelagos or island chains, which are collections of islands. These chains are thought to form from volcanic hotspots, areas of the lithosphere where the mantle is hotter than the surrounding area. These hotspots would give rise to volcanoes whose lava would form the rock the islands are made of. For some islands, the movement of tectonic plates above stationary hotspots would form islands in a linear chain, with the islands further away from the hotspot being progressively older and more eroded, before disappearing under the sea entirely. An example is the Hawaiian Islands, with the oldest island Kure Atoll being 25 million years old, and the youngest, Hawaii, still being an active volcano. However, not all island chains are formed this way. Some may be formed all at once by fractures in the tectonic plates themselves simultaneously creating multiple islands. One supporting piece of evidence is that of the Line Islands, which are all estimated to be 8 million years old, rather than being different ages.

Other island chains form due to being separated from existing continents. The Japanese archipelago may have been separated from Eurasia due to seafloor spreading, a phenomenon where new oceanic crust is formed, pushing away older crust. Islands sitting on the continental shelf may be called continental islands. Other islands, like those that make up New Zealand, are what remains of continents that shrank and sunk beneath the sea. It was estimated that Zealandia, the continent-like area of crust that New Zealand sits on, has had 93% of its original surface area submerged.

Some islands are formed when coral reefs grow on volcanic islands that have submerged beneath the surface. When these coral islands encircle a central lagoon, the island is known as an atoll. The formation of reefs and islands related to those reefs is aided by the buildup of sediment in shallow patches of water. In some cases, tectonic movements lifting a reef out of the water by as little as 1 meter can cause sediment to accumulate and an island to form. Barrier islands are long, sandy bars that form along shorelines due to the deposition of sediment by waves. These islands erode and grow as the wind and waves shift. Barrier islands have the effect of protecting coastal areas from severe weather because they absorb some of the energy of large waves before they can reach the shore.

Formation in freshwater
A fluvial island is an island that forms from the erosion and sedimentation of debris in rivers; almost all rivers have some form of fluvial islands. These islands may only be a few meters high, and are usually temporary. Changes in the flow speed, water level, and sediment content of the river may effect the rate of fluvial island formation and depletion. Permanent river islands also exist, the largest of which (that is completely inland) is Bananal Island, which has a maximum width of 55 kilometers.

Lakes form for a variety of reasons, including glaciers, plate tectonics, and volcanism. Lake islands can form as part of these processes.

Life on islands
The biology of islands has been the subject of study since the time of Charles Darwin in the 1800s. The species he observed on the Galápagos Islands contributed to the theory of natural selection. While islands vary greatly in terms of climate, habitabiltiy, origin, and the types of life that live on the island, they have in common some form of isolation from the mainland due to water. Continental islands, islands that were at one point connected to a continent, are expected to share a common history of plant and animal life up until the point that the island broke away from the continent. For example, the presence of freshwater fish on an island surrounded by ocean would indicate that it once was attached to a continent, since these fish cannot traverse the ocean on their own. Over the course of time, evolution and extinction changes the nature of animal life on a continental island, but only once it splits from the mainland. Islands such as Japan were (in evolutionary terms) recently connected to the mainland, whereas islands like Madagascar has probably been an island since the Triassic period. Oceanic islands, ones that have never been connected to shore, are only populated by life that can cross the sea. This means that any animals present on the island had to have flown there, in the case of birds or bats, were carried by such animals, or were carried in a sea current. Tropical storms have the capacity to transport species over great distances. Freshwater fish and large mammals are in most cases only seen only at distances of about 40 km from shore, whereas bats, insects, and spiders have traveled as far as 3200 km. The result of this is that older oceanic islands have animals and plants that have evolved differently than their cousins that are not isolated. There also may be evolutionary divergence between species among individual islands on archipelagos, since the oceanic barriers between islands that are still close in distance may force species to evolve seperately, with occasional periods of mixing between species.

The diverse and unique collection of species on islands is threatened by human activity. Agriculture, trade, and other systems introduce non-native life to islands that could not have naturally reached it. This results in an introduction of invasive species to ecosystems that already may be especially small and fragile.

History of exploration
The first evidence of humans colonizing islands probably occurred in the Paleolithic era, 100,000 to 200,000 years ago. Reaching the Indonesian islands of Flores and Timor would have required crossing distances of water of at least 29 km. The next notable island to be colonized is Australia, having been settled 10,000 years ago via a similar water crossing. Some islands, such as Honshu, were probably connected to the mainland with a land bridge that allowed humans to colonize it before it became an island. The first people to colonize oceanic islands at scale were the Polynesians. Many of the previous island settlements required travelling distances of less than 100km, whereas Polynesians may have traveled 2000-3200 km to settle islands such as Tahiti. They would send navigators to sail the ocean without the aid of navigational instruments to discover new islands for settlement. Between 1100 and 800 BC, Polynesians sailed East from New Guinea and the Solomon Islands and reached the islands that make up the modern-day Fiji and Samoa. The furthest extent of this migration would be Easter Island in the East, and New Zealand in the South, with New Zealand's first settlements between 1250 and 1300. Other cultures, such as Native Americans and various populations in Africa, were also able to colonize islands.

Historians have sought to understand why some remote islands have always been uninhabited, while others, especially in the Pacific Ocean, have long been populated by humans. Generally, small islands that cannot sustain populations on their own can still be habitable if they are within a "commuting" distance to an island that has enough resources to be sustainable. This also implies that larger islands are more likely to be able to sustain humans and thus are more likely to have been settled. Island chains may be easier for a navigator to find than a single island, since the presence of an island is marked by seabirds, differences in cloud and weather patterns, as well as changes in the direction of waves. It is also possible for human populations to have gone extinct on islands, evidenced by explorers finding islands that show evidence of habitation but no life.

Not all islands were or are inhabited by maritime cultures. In the past, some societies were found to have lost their seafaring ability over time, such as the case of the Canary Islands, which were occupied by an indigenous people since the island's first discovery in the first century until being conquered by the Spanish Empire in 1496. It has been hypothesized that since the inhabitants had little incentive for trade and had little to any contact with the mainland, they had no need for boats.

The motivation for island exploration has been the subject of research and debate. Some early historians previously argued that early island colonizations were unintentional, perhaps by a raft being swept out to sea. Others compare the motivations of Polynesian and similar explorers with those of Christopher Columbus, the explorer who sailed westward over the Atlantic Ocean in search of an alternate route to the East Indies. These historians theorize that successful explorers were rewarded with recognition and wealth, leading others to attempt possibly dangerous expeditions to discover more islands, usually with poor results.

Lifestyle
With the exception of Greenland, islands make up 1.47% of the world's surface area. Despite this, 10% of the world's population lives on islands. The study of the culture of islands is known as island studies. The interest in the study of islands is due to their unique cultures and natural environments that differ from mainland cultures. This is for a few reasons: First, the obvious political and geographic isolation from mainland cultures. Second, unique restraints on resources and ecology creating marine-focused cultures with a focus on fishing and sailing. Third, a lasting historical and political significance of islands.

Diet
The Polynesian diet got most of its protein from fishing. Polynesians were known to fish close to shore, as well as in deep water. It was reported that Rapa Nui people were known to fish as far as 500 km from shore at coral reefs. Spear, line, and net fishing were all used, to catch tuna as well as sharks and stingrays. Island cultures also cultivate native and non-native crops. Polynesians grew the native yam, taro, breadfruit, banana, coconut and other fruits and vegetables. Different island climates made different resoruces more important, such as the Hawaiian islands being home to irrigated fields of taro, whereas in some islands, like Tahiti, breadfruit was more widely cultivated and fermented in order to preserve it. There is archeological evidence that Canary Islanders would chew the roots of ferns for sustenance, a practice that wore heavily on their molars. These islanders would also grow barley and raised livestock such as goats.

Political significance
Many island nations, especially in the Pacific, generally have little land and a restricted set of natural resources. However, these nations control some of the largest fisheries in the world, deposits of copper, gold, and nickel, as well as oil deposits. The natural beauty of island nations also makes them a magnet for tourism. Islands also have geopolitical value for naval bases, weapons testing, and general territorial control. One such example is French Polynesia, a territory that receives substantial military expenditure and aid from France.

Colonization
Since the first discoveries of Polynesian, Micronesian, and other islands by Westerners, these nations have been the subject of colonization. Islands were the target of Christian missionaries. These missionaries faced resistance, but found success when some local chiefs used European support to centralize power. Through military and poltiical means, European states placed most of Oceania in under colonial administration. Pohnpei was colonized by Spain as early as 1526. It changed hands from Germany to Japan to the United States before joining the Federated States of Micronesia in 1982, maintaining a "free association" status with the U.S. Guam was a Spanish territory until 1898, and now is a unincorporated territory of the U.S.

The decolonization era saw many island states achieve independence or some form of self-governance. Nuclear weapons testing on the Marshall Islands left many atolls destroyed or uninhabitable, causing the forced displacement of people from their home islands as well as increases in cancer rates due to radiation. Colonization has resulted in a decline of observance of traditional cultural practices in places such as Hawaii, where Native Hawaiians are now a minority. Colonization has also been criticized for introducing capitalist systems and Western forms of government.

Tourism
Islands have long been a popular target for tourism, thanks to their unique climates, cultures, and natural beauty. However, islands may suffer from poor transportation connectivity from airplanes and boats and strains on infrastructure from tourist activity. Islands in colder climates often rely on seasonal tourists seeking to enjoy nature or local cultures, and may only be one aspect of an island's economy. In contrast, tourism on tropical islands can often make up the majority of the local economy and built environment. These islands sometimes also require consistent foreign aid on top of tourism in order to ensure economic growth. This reliance can result in social inequality and environmental degradation. During tourism downturns, these economies struggle to make up the lost inflow of cash with other industries.

Climate change
Climate change threatens human development on islands due to sea level rise, more dangerous tropical cyclones, coral bleaching, and an increase in invasive species. For example, in 2017 Hurricane Maria caused a loss of almost all the infrastructure in Dominica. Sea level rise and other climate changes can reduce freshwater reserves, resulting in droughts. These risks are expected to decrease the habitability of islands, especially small ones. Beyond risks to human life, plant and animal life are threatened. It has been estimated that almost 50% of land species threatened by extinction live on islands. Coral bleaching is expected to occur with more frequency, threatening marine ecosystems, some of which island economies are dependent on.

Some islands that are low-lying may cease to exist given high enough amounts of sea level rise. Tuvalu received media attention for a press conference publicizing the ongoing submerging of the island country. Tuvalu signed a cooperation agreement with Australia agreeing to allow citizens of 280 citizens of Tuvalu annually to become permanent residents of Australia. The Marshall Islands, a country of 1,156 islands, have also been identified as a country that may be existentially threatened by rising seas.

Increasing intensity of tropical storms also increases the distances and frequency with with invasive species may be transported to islands. Floodwaters from these storms may also wash plants further inland than they would travel on their own, introducing them to new habitats. One example is the apple snail, initially introduced to the U.S. by aquarium owners. It has since been transported by hurricanes across the Gulf Coast and neighboring islands. These species compete for resources with native animals, and some may grow so densely that they displace other forms of existing life.

Artificial islands
For hundreds of years, islands have been created through land reclamation. One of the first recorded instances of this when people of the Solomon Islands created eighty such islands by piling coral and rock in the Lau Lagoon. One traditional way of constucting islands is with the use of a revetment. Sandbags or stones are dropped with a barge into the sea to bring the land level slightly out of the water. The island area is then filled with sand or gravel, followed by a construction of this revetment to hold it together. Islands have also been constructed with a permanent caisson, a steel or concrete structure built in a closed loop and then filled with sand.

Some modern islands have been constructedby pouring millions of tons of sand into the sea, such as with Pearl Island in Qatar or the Palm Islands in Dubai. These islands are usually created for real estate development, and are sold for private ownership or construction of housing. Offshore oil platforms have also been described as a type of island. Some atolls have been covered in concrete to create artificial islands for military purposes, such as those created by China in the South China Sea. These atolls were previously low-tide elevations, landmasses that are only above water during low tide. The United Nations Convention on the Law of the Sea indicates that these islands may not have the same legal status as a naturally occuring island, and as such may not confer the same legal rights.