Island

An island or isle is a piece of land completely surrounded by water, distinct from a continent. There are two main types: continental islands, which were once part of a continent and split away due to plate tectonics, and oceanic islands, which have never been connected to a continent. Oceanic islands can form from volcanic activity, grow from coral reefs into atolls, or be created from sediment along coastlines, forming barrier islands. River islands are formed by sediment in rivers, and artificial islands are built by people for various purposes, including land reclamation projects.

Islands support a wide variety of plant and animal life. Because oceanic islands are separated by the sea, species that arrive there often evolve in isolation, developing unique traits. Continental islands share many species with the mainland they came from, though over time these species may change due to natural selection.

Humans have lived on islands and traveled between them for thousands of years. Some islands were first settled when they were connected to land by a land bridge or when they split from a continent, while others were reached by boat. Today, about 10% of the world’s people live on islands. Many islands are popular for tourism because of their natural beauty, peaceful settings, and unique cultures.

Sadly, islands face serious threats from climate change. Rising sea levels could completely cover some island nations like the Maldives, the Marshall Islands, and Tuvalu. Stronger and more frequent tropical cyclones can destroy homes and habitats. Species that live only on islands are especially at risk of extinction. Some islands, like Taiwan, are also subjects of territorial disputes, claimed by other countries such as China.

Definition

An island is a piece of land surrounded by water on all sides, and it is different from a continent. There is no specific size that makes something an island instead of a continent. Continents are the largest pieces of land on a tectonic plate. Islands can be found in lakes, rivers, and seas. Areas of land that are only visible at low tide, but covered by water at high tide, are not usually called islands. Sometimes, islands can be connected to the mainland through land building projects.

Etymology

The word island comes from old languages. In Middle English, it was written as iland, and even earlier in Old English as igland. This word is related to words in other languages, like the Swedish word ö and the German word Aue.

Over time, the spelling changed to include an “s” because people mistakenly thought it was related to the Old French word isle, which came from the Latin word insula.

Geology

Islands often appear in groups called archipelagos or island chains. These chains can form from volcanic hotspots—areas where the Earth's layer is hotter than around it. Hotspots can create volcanoes, and the lava from these volcanoes becomes the rock of islands. When tectonic plates move over these stationary hotspots, they can form a line of islands, with the ones farther away being older and worn down. An example is the Hawaiian Islands, where the oldest island is 25 million years old, and the youngest, Hawaii, is still an active volcano.

Some islands were once part of continents but got separated. Others form from coral reefs growing on submerged volcanic islands. When these coral islands circle a lagoon, they are called atolls. Barrier islands are long, sandy bars that form along coastlines from sediment carried by waves. They help protect the coast by absorbing wave energy.

Life on islands

The field of insular biogeography studies how plants and animals change and grow on islands. Scientists use islands to learn about how animals and plants change over time. Island ecology looks at how living things and their homes work together. This has helped us learn a lot about nature since the time of Charles Darwin.

Endemism

Main article: Endemism

Endemism means that some plants or animals can only be found in one special place. Islands are great places for this because water keeps animals and plants separated. Islands have many unique species, which helps the world's nature stay rich and healthy. But islands usually have fewer total types of species than big lands do. Bigger islands can hold more kinds of life because they have more space and food.

Dispersal

Oceanic islands, which never touched land, only have animals that can fly, like birds and bats, or those carried by animals or ocean currents. Big storms can carry animals far away. For example, in 1995, fifteen iguanas floated to Anguilla in the Caribbean on trees after a storm. Plants can also travel far across the ocean. New Zealand and Australia share 200 plant types even though they are very far apart.

Continental islands used to be part of a bigger land. They may have animals like freshwater fish that cannot live in the ocean, showing they were once connected to land. Over time, these animals change and some may disappear.

Evolution on island groups

When animals first arrive on a group of islands, they often change quickly into new types. This is called adaptive radiation. They change because they find new foods or less competition.

A famous example is Darwin's finches from the Galápagos Islands. These birds developed different kinds of beaks to eat different foods. The large ground finch cracks seeds and eats fruit, while the Genovesa cactus finch eats parts of cacti. Similar changes happen on islands around the world.

The island rule

Animals on islands often change size in special ways. Small animals like rodents often grow larger, while bigger animals like hippos often become smaller. Scientists think this happens because islands have fewer animals that might eat them and less food, so sizes change to fit the island's life better.

Darwin, the Galápagos, and natural selection

Charles Darwin used what he saw on the Galápagos Islands to help him understand how animals change over time. He visited the islands in 1835 and noticed that each island had its own kinds of animals. This helped him see that animals change to fit where they live. He would spend many years later writing about his ideas in On the Origin of Species.

Humans and islands

History of exploration

See also: Sea § Humans and the sea

Humans first began living on islands around 100,000 to 200,000 years ago. To reach islands like Flores and Timor, people had to cross at least 29 km (18 mi) of water. Some islands, such as Honshu, might have been connected to the mainland by land bridges, making it easier for people to move there.

The first people to settle faraway islands were the Polynesians. They traveled huge distances—up to 3,200 km (2,000 mi)—to reach places like Tahiti. These travelers sailed without modern tools to find new homes. Between 1100 and 800 BC, Polynesians moved from New Guinea and the Solomon Islands to settle in Fiji and Samoa. Their journeys reached as far as Easter Island in the east and New Zealand in the south, where the first people arrived between 1250 and 1300.

Lifestyle

About 10% of the world’s people live on islands. Islands often have special cultures and ways of life because they are separated from larger lands. This separation, along with limited resources, has shaped island cultures to focus on the sea, fishing, and sailing. Islands also have important histories and meanings for many people.

Diet

People on islands like those settled by Polynesians got most of their food from the sea. They fished near the shore and far out in the ocean, using spears, lines, and nets to catch fish such as tuna, sharks, and stingrays. They also grew crops like yam, taro, breadfruit, banana, and coconut. Different islands grew different foods based on their climate. For example, Hawaii had fields of taro, while other islands grew more breadfruit. Some islanders also ate roots from ferns and raised animals like goats.

Island nations and territories

Many island nations have small amounts of land but control big areas of the ocean, rich in fish and minerals like copper, gold, and nickel. Some also have oil deposits. Their beautiful landscapes make them popular for tourism. Islands can also be important for military bases and control of sea routes. For example, French Polynesia receives support from France. Other Pacific island nations like Palau, Federated States of Micronesia, and the Marshall Islands have special agreements with the United States.

Colonization

Islands have often been taken over by other countries. Beginning in the 1500s, European powers brought their influence to many island groups. For example, Pohnpei was first controlled by Spain, then Germany, Japan, and later the United States before becoming part of the Federated States of Micronesia. Guam was a Spanish colony until 1898 and is now a U.S. territory.

After World War II, many island nations gained independence or more self-rule. However, some islands suffered from nuclear testing, which damaged their lands and health. Colonization also changed many island cultures, sometimes reducing the practice of traditional ways of life. These changes can make it hard for some island nations to grow their economies in the modern world.

Tourism

Islands are often popular places for people to visit because of their beautiful scenes, cultures, and natural surroundings. But islands can struggle with transportation and may have problems when too many tourists come. In colder islands, tourism is seasonal, while in tropical islands, tourism can be a main source of money. However, relying too much on tourism can cause unfairness and harm to the environment. When tourism drops, these islands have a hard time replacing that lost income.

Threats to islands

Further information: Effects of climate change on small island countries

Climate change can cause big problems for islands. Rising sea levels and stronger tropical cyclones make life harder for people living there. Coral bleaching harms the ocean life that many islands depend on, and more invasive species can arrive, causing trouble for plants and animals.

Some very low islands might even disappear if the sea rises too much. For example, Tuvalu has talked about moving some of its people to Australia. The Marshall Islands are also worried about rising seas. Stronger storms can carry new plants and animals to islands, where they might crowd out the native species. For instance, an apple snail brought by aquarium owners can spread to new places during hurricanes, changing the local environment.

Artificial islands

Main article: Artificial island

People have been making islands for hundreds of years by adding land where there was none. One early example is from the people of the Solomon Islands, who built eighty islands in the Lau Lagoon using coral and rock. The first known permanent artificial island is Al-Sayah in Bahrain, made over 1,200 years ago.

Today, islands are often built by pouring huge amounts of sand into the sea. Examples include Pearl Island in Qatar and the Palm Islands in Dubai. These islands are usually made for building homes or other structures. Some islands are also used for special purposes, like placing oil platforms or for military use, such as islands built by China in the South China Sea.