By Edward O. Wilson Known as the biosphere to scientists and as the creation to theologians, all of life together consists of a membrane around earth so thin that it cannot be seen edgewise from a satellite yet so prodigiously diverse that only a tiny fraction of species have been discovered and named. The products of billions of years of evolution, organisms occupy virtually every square centimeter of the planet's surfaces and fill nearly every imaginable niche.
Biologists estimate that more than half the species occur in the tropical rain forests.
At the other extreme, the McMurdo Dry Valleys of Antarctica, with the poorest and coldest soils in the world, still harbor sparse communities of bacteria, fungi and microscopic invertebrate animals. In the most frigid polar waters, fish and other animals flourish, their blood kept fluid by biochemical antifreezes. Populations of bacteria live in the spumes of volcanic thermal vents on the ocean floor, multiplying in water above the boiling point. At the top are the ecosystems, such as rain forests, coral reefs and lakes. At the bottom are the variety of genes making up the heredity of each species.