Has the Earth's sixth mass extinction already arrived?
Wednesday, March 2, 2011 - 13:31
in Paleontology & Archaeology
With the steep decline in populations of many animal species, from frogs and fish to tigers, some scientists have warned that Earth is on the brink of a mass extinction like those that occurred only five times before during the past 540 million years. Each of these 'Big Five' saw three-quarters or more of all animal species go extinct.