Palaeontologists recognize five mass extinction events from the fossil record in the past 540 million years. It is suggested that a sixth mass extinction is under way, based on the known species losses over the past few millenia.
Mass extinctions have been characterised as times when Mother Earth loses more than three-quarters of its species in a geologically short time frame. With the most recent and probably well-known, the Cretaceous mass extinction — ending some 65 million years ago, wiping out the dinosaur. Researchers, led by Anthony Barnosky, have reviewed available palaeontological data, fossil and current, and conclude that current extinction rates are enormous, though the dramatic loss of species cannot be qualified as mass extinction yet. Nonetheless, the rate at which species going extinct highlights the need for improved nature and species conservation measures. According a worst case scenario the sixth mass extinction starts in 240 to 540 years, and a less pessimistic view estimates the beginning at 4.500 to 11.000 years. Even in this ‘positive’ scenario all now critically endangered animal species (1939, of which 188 mammals; IUCN Red List 2010.4) will go extinct in the next five centuries.
(Source: Nature, 03.03.2011)
