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Metamorphosis
Many animals such as insects, amphibians, jellyfish and mollusks go through metamorphosis as they development from babies to adults. Scientists have identified two types of metamorphosis. In complete metamorphosis, an organism's development has four stages. A worm-like larva hatches from an egg. After a period of feeding, the larva builds itself a protective shell. Inside the shell, the resting pupa develops an adult body structure. Once the transformation is complete, an adult emerges from the shell. In incomplete metamorphosis, an organism's development has three stages. A tiny nymph, which resembles its parents but lacks adult characteristics such as wings, hatches from an egg. After a period of growth and development, the nymph molts, or sheds its skin, and takes on adult characteristics.
Butterflies
Butterflies undergo complete metamorphosis. The female lays about 600 eggs around a plant stem. Larval butterflies, or caterpillars, emerge from the eggs and begin feeding. They can eat twice their own body weight in a day. Caterpillars will molt about four times as they grow. The fully grown caterpillar forms a protective shell called a chrysalis around its body. Inside, the dormant caterpillar, or pupa, slowly develops adult characteristics such as wings. The fully developed butterfly sucks in air and splits open its protective shell by expanding its body. After struggling out of the chrysalis, the butterfly expands its wings by pumping them full of blood. The wings dry and hardened in the warm sun.
Metamorphism
Metamorphism occurs when rock is exposed to tremendous heat, pressure or both. Geologists divide metamorphic rocks into two broad categories. Regional metamorphic rocks are found in mountainous regions and are formed by pressure. Different types of metamorphic rock are created by different amounts of pressure. The deeper beneath the surface, the higher the pressure. Higher amounts of pressure create greater amounts of change. Thermal metamorphic rock, or contact metamorphic rock, is formed by great heat. When molten rock rises towards the surface, every empty space fills with molten rock. The heat causes nearby rock to recrystallize, or change chemical composition, and form new rock.
Types of Metamorphic Rock
Examples of regional metamorphic rock include shale, slate, schist and gneiss. Shale forms from mud under relatively low pressures about three miles down. Slate, a fine-grained rock used as roof tile or paving stone, forms when shale is exposed to higher pressure. At even higher pressure, a medium-grained rock called schist is formed. Schist often breaks into layers and contains crystals. A coarse-grained, layered rock called gneiss forms at even higher temperatures and pressures than schist. Examples of thermal metamorphic rock include marble and quartzite. Marble forms when heat causes the recrystallization of limestone. Sandstone, which contains quartz, recrystallizes into quartzite.