Wednesday, December 5, 2012

Life on Earth & Extinction

http://images.nationalgeographic.com/wpf/media-live/photos/000/010/cache/mass-extinction_1077_600x450.jpg
Life on Earth has been around for millions of years, but not without imperfection. As long as there is life on Earth, extinction will always be a determining factor. It is considered the fate of all species eventually. As scientists continue to study Earth and its history they continue to find evidence that there is a steady background extinction rate. Many episodes of mass extinction were also present. Evidence (fossils) shows that over the last 600 million years, at least 5 mass extinctions have occurred that scientists can prove actually happened. During these extinctions, at least 50% of the Earth’s population was wiped out. Talk about counting your losses..2 of the most extreme were the Permian and Cretaceous extinctions. An unsettled Earth is what caused the Permian extinction. By unsettled Earth I mean: volcanoes everywhere, extremely hot climate, mixing of oceans, and reduced oxygen levels. No wonder 96% of shallow water species died! The Cretaceous extinction is the more commonly known extinction that occurred. Remember when your teacher taught you that an asteroid crashing into Earth caused the extinction of all dinosaurs? Well, they were right. And the Cretaceous extinction is exactly what they were referring to. The asteroid that struck Earth 65 million years ago blocked sunlight and disrupted the climate which caused 50% of all animals to perish (including dinosaurs). Now, we have to carefully observe what is going on around us because scientists believe that a 6th mass extinction may be under way! :/
http://blogs.discovery.com/.a/6a00d8341bf67c53ef017742dbaf86970d-800wi


Source: Class Notes-Chapter 15-Tracing Evolutionary History

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