Our senses

What's that smell? Do you hear that noise? Taste this! Look at me! Feel this, isn't it soft? When you hear, or even use these phrases, you probably don't stop to think about why we use them. Well, it's because of our senses. Without us even knowing, our sense organs (nose, eyes, ears, tongue, and skin) are taking in information and sending it to the brain for processing. If we didn't have them, we would not be able to smell, see, hear, taste, or touch anything! Talk about a boring life. Our senses are the physical means by which all living things see, hear, smell, taste, and touch. Each sense collects informaton about the world and detects changes within the body. Both people and animals get all of their knowledge from their senses, and that is why our senses are so important. All senses depend on the working nervous system. Our sense organs start to work when something stimulates special nerve cells called receptors in a sense organ. We have five main sense organs. They are the eyes, nose, ears, tongue, and skin. Once stimulated, the receptors send nerve impulses along sensory nerves to the brain. Your brain then tells you what the stimulus is. For example, your sound receptors would be bombarded by billions of sound waves. When these signals reach the part of the brain called the cerebral cortex, we become conscious of the sounds.

The Biosphere

The term "Biosphere" was coined by Russian scientist Vladimir Vernadsky in the 1929. The biosphere is the life zone of the Earth and includes all living organisms, including man, and all organic matter that has not yet decomposed. Life evolved on earth during its early history between 4.5 and 3.8 billion years ago and the biosphere readily distinguishes our planet from all others in the solar system. The chemical reactions of life (e.g., photosynthesis-respiration, carbonate precipitation, etc.) have also imparted a strong signal on the chemical composition of the atmosphere, transforming the atmosphere from reducing conditions to and oxidizing environment with free oxygen. The biosphere is structured into a hierarchy known as the food chain whereby all life is dependent upon the first tier (i.e. mainly the primary producers that are capable of photosynthesis). Energy and mass is transferred from one level of the food chain to the next with an efficiency of about 10%. All organisms are intrinsically linked to their physical environment and the relationship between an organism and its environment is the study of ecology. The biosphere can be divided into distinct ecosystems that represent the interactions between a group of organisms forming a trophic pyramid and the environment or habitat in which they live.

Atmosphere

The atmosphere is the gasesous envelope that surrounds the Earth and constitutes the transition between its surface and the vacuum of space. The atmosphere consists of a mixture of gases composed primarily of nitrogen, oxygen, carbon dioxide, and water vapor. It extends some 500 km above the surface of the Earth and the lower level (troposphere) constitutes the climate system that maintains the conditions suitable for life on the planet's surface. The next atmospheric level, the stratosphere (12 to 48 km), contains the ozone layer that protects life on the planet by filtering harmful ultraviolet radiation from the Sun. Since the Industrial Revolution, man has been altering the composition of the atmosphere by the burning of fossil fuels. Concern has been growing about rising concentrations of carbon dioxide, methane, nitrous oxide, and chloroflurocarbons in the atmosphere because these "greenhouse" gases trap heat energy emitted from the earth surface and increase global temperatures (global warming). In addition, chloroflurocarbons are effective at depleting the Earth's ozone shield that protects the earth surface from the harmful effects of ultraviolet radiation