Biodiversity or Biological Diversity, sum of all the different species of animals, plants, fungi, and microbial organisms living on Earth and the variety of habitats in which they live. Scientists estimate that upwards of 10 million—and some suggest more than 100 million—different species inhabit the Earth. Each species is adapted to its unique niche in the environment, from the peaks of mountains to the depths of deep-sea hydrothermal vents, and from polar ice caps to tropical rain forests. Perhaps the greatest value of biodiversity is yet unknown. Scientists have discovered and named only 1.75 million species—less than 20 percent of those estimated to exist. And of those identified, only a fraction have been examined for potential medicinal, agricultural, or industrial value. Most biologists agree that life on Earth is now faced with the most severe extinction episode since the event that drove the dinosaurs to extinction 65 million years ago. Species of plants, animals, fungi, and microscopic organisms such as bacteria are being lost at alarming rates—so many, in fact, that biologists estimate that three species go extinct every hour.
Source: Taken from Encarta