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Topic 7:The Sixth Extinction There have been five major extinctions to date, (Major declines in biodiversity. Scientists have determined that the rate of extinction is approximately one species per year over the history of life on Earth. They think that today the rate may be closer to 70 extinctions per day. This is resulting in decreasing biodiversity all over the planet. There is debate as to whether or not a sixth extinction is occurring today. 1. Cretaceous – Paleogene: Non – avian dinosaurs 2. Triassic – Jurrassic: Non – dinosaurian archosaurs, (crocodiles), and large amphibians 3. Permian – Triassic :(largest extinction): Ended all mammal – like reptiles 4. Late Devonian: 50% of all genera and 70% of all plant species 5. Ordovician – Silurian: 27% of all families, 57% of all genera, 70% of all plant species Human Impacts on Biodiversity Different areas on Earth support biodiversity better than others. Areas where there is a lot of heat, light and rainfall promote better plant growth which allows for more complex food chains. Changes in environments and climates caused by humans can greatly affect species and in turn the biodiversity of an area. http://vimeo.com/12448488 Disappearing Habitats Scientists use bioindicator species to measure the human impact on the environment. Usually the first species that are effected by human interference are large carnivores. In order to preserve these species Scientists believe that their habitats must be protected. Human Impact on Rain Forest Ecosystems The global population is increasing because people now live longer than they used to in many countries. Improvements in food sources, medicines, and health care has aided this increase. The larger the population becomes the more demands are put onto the environment and ultimately more pollution is created. The Population Explosion Since very diverse areas tend to be in developing nations they are often more greatly affected by population increases than other areas. Tropical rain forests are one of the areas the are greatly affected. Land is being cleared for ranches, farms and coffee plantations. When even a small area of rainforest is cleared it can result in the extinction of a specialist organism. Soil conditions in the rain forest are poor meaning that they don’t have adequate nutrients. Since the soil conditions are poor farms, ranches and plantations only last for a couple of years. This means that species are lost forever in order to supply food etc. for a short period of time. Human Activities and Extinctions Over hunting has been responsible for the extinction of animals all over the world. (Wolly Mammoth, Passenger Pigeon, Bison)