ABSTRACT
The earth and its atmospheric envelope constitute a majestic system, maintained in stability by a web of physical and chemical interactions, all driven ultimately by energy from the sun. Radiation from the sun warms the earth making life pos- sible; differential warming between the equator and the poles drives large scale convective circulation in the oceans and the atmosphere determining regional climates, seasons and rainfall patterns, storms and droughts. Energy from the sun evaporates water from the surface of the oceans which becomes condensed in clouds and precipitated back to earth as rain or snow to feed terrestrial plants and animals, enter streams and groundwater systems, and eventually return to the ocean. Light energy from the sun drives processes of photosynthesis upon which life on earth depends. Green plants on land combine the simple chemical mol- ecules of carbon dioxide and water with energy from sunlight to produce carbo- hydrates (such as glucose) and oxygen.
