Biologists have organized all the life on Earth into four levels of complexity and interaction. In this schema, species of organisms live in "communities" where they compete for food and habitat. At the next level, communities interact in an "ecosystem." The ecosystem includes weather and geology of the area in addition to plants and animals. For example a specific forest qualifies as an ecosystem. Then, taken together, those ecosystems that share major characteristics of terrain create a biome. A biome is united by temperature, precipitation, soil type, vegetation, latitude, and elevation. At the most macroscopic level reigns the biosphere of our Earth that contains all the life we know exists in the universe.
Biomes are spread across the Earth's surface. That is, part of the Florida Everglades have more in common with India, in terms of ecosystems, than it does with Georgia right next door. Treating the world as a system of biomes allows biologists to study climate, geology, endangered species, agriculture, and many related subjects. Biomes were formed at different stages of Earth's evolution, depending on the presence of organic matter, water, plate tectonics, and where, in terms of latitude, the terrain lies. Since the Earth is tilted on its axis, and moves around the sun, latitude can tell us how much light hits the surface.
The seven major biomes are divided into six terrestrial (ground) and one aquatic (water) biome. The aquatic biome can be categorized as both marine and freshwater biomes. Sometimes freshwater lakes, rivers, streams, and underground aquifers belong to the surrounding terrestrial biome. The terrestrial biomes are tundra, rainforest, grasslands (also called prairie or steppe), taiga (boreal or coniferous forest), desert, and temperate (deciduous) forest. Some biologists define more than seven major biomes, adding chaparral, mountain, island, or tropical dry forest. Other biomes are further subdivided, such as deep ocean, open ocean, and shallow ocean marine biome, or the hot and cold deserts.
