Many other hypotheses have been proposed, such as the spread of a new disease, or simple out-competition following an especially successful biological innovation. Guardian) Tide of Extinction Threatening Sea Turtles (The East African- 2006).S. Sahney,.; Benton,.J. Based on the fossil record, the background rate of extinctions on Earth is about two to five taxonomic families of marine animals every million years. McElwain,.C.; Punyasena,.W. Daily Mail- 2010) Britain's Butterflies in Crisis (U.K. Wilson, harvard: current rate OF human activity will result IN 50 OF ALL species extinct BY 2100. Earth'S sixth mass extinction event already underway, scientists warn (U.K. Anoxic events edit Anoxic events are situations in which the middle and even the upper layers of the ocean become deficient or totally lacking in oxygen.
"Synchronism of the Siberian Traps and the Permian-Triassic Boundary". Furthermore, the PermianTriassic extinction event has been suggested to have been caused by warming. Guardian) Half Of World's Bat Species Threatened (BBC) Extinction Nears for Whales and Dolphins (BBC) 70 of Dolphin Species Face Extinction (BBC- 2005) 308,000 Whales, Dolphins, Porpoises Drown Each Year in Fishing Gear (WWF) Whales Pursued to Brink of Extinction (E/Environmental Magazine) Half of Whale. The extinctions, however, did not conform to the usual evolutionary rules regarding who survives the only factor that appears to have improved a family of organisms' chance of survival was widespread geographic colonization at the time of the event. Santa Cruz Biotic Holocaust, Norman Myers, Oxford University A Winnowing for Tomorrow's World, Norman Myers, Oxford University Planet Faces Mass Extinction, Richard Leakey Earth On Edge, Michael Novacek, American Museum of Natural History Repeating History at Our Peril, by David Suzuki, University of British Columbia. Theories regarding the causes of mass extinctions abound and are the subject of intense study and debate.