Using a globe or world map, point out that most of Earth is covered by water.
Using relief maps, show students that Earth's surface has peaks, valleys, and plateaus, some of which are underwater.
Review the three major ways islands form: A) As sea level rises, land areas may become separated by water. B) Coral reefs emerge if the sea level drops or the land underneath rises. Sand and dust accumulating on the reef form an island. C) An underwater volcano can grow until it reaches above the water surface.
Explain that during the last Ice Age more of Earth's water was frozen at the poles, which were larger than they are today. About 10,000 years ago, Earth began to warm, and the ice caps began to melt. Some land areas became islands as rising waters cut them off from a mainland. New Zealand is one such location.
Describe how coral polyps form islands. Polyps live in underwater colonies, where they protect their soft bodies by building limestone walls around them. The colonies grow and form reefs, which may emerge if sea level drops or the land underneath rises. Accumulations of sand and dust help form an island. An example of a chain of coral reef islands: the Florida Keys.
Explain how volcanism forms islands. When underwater volcanoes erupt, lava flows build up. Over time, a volcano can reach above the surface of the sea, forming an island, such as those that make up Hawaii.
Explain that an island's formation affects the kinds of plant and animal species living on it. Cut off from a mainland by rising sea level, an island is likely to have mainland species from the start. Formed by a volcano or as a coral reef, an island will have no plants or animals to begin with. Animals can reach an island traveling on logs or other objects floating in the ocean. Plants and birds usually travel by air.
Next, as have students work in pairs or groups to prepare a presentation on one island listed below. Presentations should include the island's location; a brief description of its geography; how and when the island formed; a description of at least one animal species unique to that island; and an explanation of how the species has adapted to life there.
Definition: A mound or ridge of coral and calcium deposits that forms in warm shallow seas
Context: A coral reef is a complex ecosystem that shelters many kinds of marine life.
Definition: The surface level of the sea used as a standard in calculating land elevations and sea depths
Context: A growing volcano will become an island if it rises above sea level.
Definition: A fundamental classification of living things in biology, consisting of related organisms capable of interbreeding
Context: An island's isolation limits the number and variety of its animal and plant species.
Definition: The force, activity, or phenomena associated with volcanoes
Context: Volcanism created the Hawaiian Islands.
This lesson plan addresses the following national standard: