Biodiversity

Biodiversity (biological diversity) is the optimal number and relative abundance of native species and individual organisms living in a defined area, including variation at the genetic, species, habitat, and landscape levels.

How Many Species Are Known?

There are approximately 1.4 million to 1.75 million species that have been identified by scientists. [source] The known species tend to be physically larger than species not yet identified.

How Many Species Are Not Yet Known?

Estimates of the total number of species globally range from 2 million to 140 million, with various scientists embracing the 10 million to 14 million mid-range.  Using this range as the probable total, 82 percent to 90 percent of all species on Earth are not yet identified.

Given the current rate of extinction, millions of species may be extinct before humans know they ever existed.

What Species are Most at Risk?

The species most important to humans, namely humans themselves (Homo sapiens sapiens) have only been on Earth for 130,000 years. [source]  Having arrived late at the biodiversity party, and having behaved badly in recent time, humans may depart the scene prematurely as a result of the cascading collapse of vital ecosystems.