My Science School

 Tortoises belong to an ancient group of reptiles that first appeared on the planet about 250 million years ago.

Giant tortoises are found on some remote islands, especially in the Galapagos Islands, Madagascar, and the Aldabra Atoll. These tortoises probably evolved from normal size tortoises that came over from the mainland. It takes a giant tortoise about 20 years to reach breeding size, and they can weigh over 400 kg!

Their eggs are about the size of a tennis ball, and are buried in moist sand, or loose soil. Some species are vegetarians, and giant tortoises can survive for long periods with little food or water. They have the longest lifespan of all vertebrates... they can live as long as I 00 years. 

Birds usually have many enemies, and it is possible for them to escape from these enemies by flying away.

However, on islands that are cut off from mainland, birds are comparatively safe. Their enemies are few in number, for it is not possible for predators to reach an island, except by flying or swimming.

As a result, many species of birds on remote islands lose their ability to fly. The Tasmanian native hen, the cassowary, the takahe, and the flightless cormorant are some such birds.

Some species of birds evolve wings on the mainland, but after centuries on an island, become flightless. Some flightless birds have become extinct. The dodo, which was unique to Mauritius, is one such example. Since it could not fly, it was easy to catch, and as its meat was very tasty, the Dutch sailors on the island killed and ate so many, that the species became extinct! 

 

A group of islands called the Galapagos Islands lie off the west coast of South America. These islands are totally isolated, and cut off from other land masses.

 As a result, they are unique in many ways, and are home to creatures and plants that have evolved to become one of a kind. The Galapagos Islands are located where three major ocean currents intersect, and they are also affected by four other ocean cur rents as well.

Consequently, their marine life is like none other in the world. Here you will find marine iguanas, Galapagos penguins and flightless cormorants, as well as less familiar animals such as bull head sharks, red lipped batfish, and many more. Half of the plants, and almost all the reptiles on these islands, are found only here and nowhere else on the planet!

Since islands are completely surrounded by water, they are totally isolated from other land masses, their vegetation, and wildlife.

 Plants and animals from a nearby mainland can reach an Island in different ways. Seeds can be carried to an island by the wind. Sometimes, seed capsules like those of the coconut, are washed ashore by the waves.

 These seeds take root on the island, and grow into plants. People who come to inhabit the island also bring saplings and plant them. The new plants often adapt to the different conditions found on the island, and become one of a kind species, not found anywhere else in the world.

Similarly, many islands have animals that have adapted themselves to become a new species that is unique to that particular island. Lemurs, Tasmanian devils, and Galapagos penguins are some examples of such animals. Tuatara is a very rare creature that is found only in New Zealand. 

A coral reef is essentially a huge, diverse underwater community. Many are built on limestone deposits that have been left behind by living—and decaying — creatures.

An atoll is a very specific type of coral reef. Atolls are circular coral reefs that surround a lagoon completely, or partially. They may also have an island or a handful of small islands in the centre. An atoll is formed around an underwater volcano. When the volcano erupts, it creates piles of lava on the sea floor that will eventually rise above the water level to create the centre island.

 Corals will begin to congregate around the volcanic eruption. As thousands and millions of years pass, the volcano that originally created the centre island of the atoll will fall dormant.

However, the coral continues to grow, and attract more and more marine life forms. Most of the world's atolls are in the Pacific Ocean and Indian Ocean. 

Volcanic islands can sometimes appear suddenly. This has happened several times. For example, in November 1963, an eight km high column of steam, ash, and volcanic fumes was ejected from the ocean bed when lava started building up in the middle Atlantic sea floor.

 

Artificial islands are man-made islands. Such islands have been created by expanding existing islets which are very tiny islands. This can be done by draining the water around an islet, so as to create more land.

Artificial islands can also be built by construction on existing reefs, or by joining together several natural islets into a bigger island. Thus, they vary widely in size, from tiny islets that have been created to hold just a single pillar, building, or other structure, to those that support entire communities.

Artificial islands can also be created from material brought in from elsewhere. Dubai's huge artificial islands are shaped like palm trees, and a map of the world.

Artificial islands are not a new concept. Even in the 14th century, the Nahua people created their capital, Tenochtitlan, on an artificial island in Lake Texcoco. Today, Mexico City sits on the remains of this ancient capital. 

Barrier islands are long, thin, and sandy islands that run parallel to the coast. Between a barrier island and the main-land, there will be a calm, protected body of water such as a lagoon or bay.

In order for barrier islands to form, several conditions must be met. First, there must be a source of sand to build the island. Next, the coastline must have a broad, gentle slope. Finally, the forces of waves, tides, and currents must be strong enough to move the sand, so as to form an island.

Once formed, barrier islands are dynamic. The winds and waves constantly rework, and move the barrier island sand. Changes in sea level also affect these islands. Each barrier island has a shoreline that faces the open sea, and receives the full force of waves. This shoreline is often called the beach. Behind the beach, there will be sand dunes.

 

Coral islands are special, because they are made up of the skeletons of living creatures called coral polyps.

Millions of these tiny animals build tough shell-like homes, one on top of another, to form a reef. If the sea bed rises, or the sea level falls even slightly, these reefs are left above the sea as islands.

A coral island is, therefore, a part of a coral reef. Coral islands are sometimes shaped like rings, and consist of low land, perhaps only a few metres above sea level, generally with coconut palms and surrounded by white coral sand beaches.

Most of the world's coral islands are found in the Pacific Ocean and some in the Indian Ocean. One such coral island is Maldives. 

 

 

 

 

 

 

 

 Islands can be formed by volcanic activity under the sea. Over millions of years, lava erupting from the sea floor builds up.

The lava cools rapidly as it comes in contact with the water, and forms solid rock. Each eruption from the sea floor builds up the solid rock higher and higher to form an undersea volcanic mountain. Finally, the mountain becomes so tall that it rises above the ocean's surface to create a volcanic island.

Mauna Loa is one of five volcanoes that form the Island of Hawaii. It is the most massive single mountain in the world, because of its sheer bulk.

 Mauna Loa has been erupting for at least 700,000 years, and may have emerged above sea level about 400,000 years ago. The volcano's magma comes from the Hawaii hot-spot, which has been responsible for the creation of the Hawaiian island chain over tens of millions of years. 

Continental islands lie off the large land masses that form continents. They lie on the continental shelf, which is the sloping, underwater ledge found at the edge of continents.

Continental islands were once part of a huge single land mass called Pangaea. Eventually, slow movements of the Earth's crust broke Pangaea apart into several pieces that began to drift away. When the breakup occurred, some large chunks of land split from the bigger land masses. These fragments of land that were surrounded by the sea became islands.

Greenland and Madagascar are examples of continental islands that were formed in this manner. Other continental islands were formed because of changes in the sea level.

About 18,000 years ago, ice covered large parts of our planet. As this ice began to melt, the sea level rose. The ocean flooded many low-lying areas, creating islands such as the British Isles, which were once part of mainland Europe.

While an island is surrounded by water on all sides, a peninsula is bordered by water only on three sides. A peninsula will always be connected to the mainland on one side. Peninsulas can be small, or very large. They are found on every continent.

In Europe, Portugal and Spain form the Iberian Peninsula. The Horn of Africa, which juts into the Arabian Sea, is a huge peninsula. The nations of North Korea and South Korea make up the Korean Peninsula in Eastern Asia.

 In Australia, there is the Cape York Peninsula. And of course, the Indian subcontinent forms a huge peninsula, bordered by the Arabian Sea, the Bay of Bengal, and the Indian Ocean.

Sometimes, islands are formed very close together, in clusters. Such a cluster of islands is called an archipelago.

Archipelagos can be made up of hundreds, or even thousands, of islands. These islands may differ from one another in their plant and animal life.

 Japan, Indonesia, the Philippines, New Zealand, Greece, Hawaii, Maldives, Azores, and New York City are examples of well-known archipelagos. Indonesia is the world's largest archipelago by area and population.

Continue reading "What is the difference between an island and an archipelago? "

An island is an area of land that is completely surrounded by water. Islands come in all shapes and forms. They can vary in size from a single rock, to a huge land mass.

Greenland is the world's largest island. Australia is also surrounded by water, but it is considered to be a continent, rather than an island. It is difficult to determine the world's smallest island, but some, like Singapore, are really tiny.

Islands can be found in the middle of the ocean, or just off the coast. They are also found in rivers, deltas, and lakes.

Islands are formed in different ways, and they are classified according to how they came into existence. Many islands have flora and fauna that are unique to them, and found nowhere else in the world.