Biodiversity is the variety and differences among living organisms from all sources, including terrestrial, marine, and other aquatic ecosystems and the ecological complexes of which they are a part. It is virtually synonymous with “Life on earth”. Biologists most often define "biological diversity" or "biodiversity" as the "totality of genes, species, and ecosystems of a region". The biodiversity found on Earth today consists of many millions of distinct biological species, which is the product of nearly 3.5 billion years of evolution