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This timeline of evolution of life represents the current scientific theory outlining the major events during the development of life on planet Earth. In biology, evolution is any change across successive generations in the heritable characteristics of biological populations. Evolutionary processes give rise to diversity at every level of biological organization, from kingdoms to species, and individual organisms and molecules, such as DNA and proteins. The similarities between all present day organisms indicate the presence of a common ancestor from which all known species, living and extinct, have diverged through the process of evolution. More than 99 percent of all species, amounting to over five billion species, that ever lived on Earth are estimated to be extinct. Estimates on the number of Earth's current species range from 10 million to 14 million, of which about 1.2 million have been documented and over 86 percent have not yet been described. While the dates given in this article are estimates based on scientific evidence, there has been controversy between more traditional views of increased biodiversity through a cone of diversity with the passing of time and the view that the basic pattern on Earth has been one of decimation and diversification and that in certain past times, such as the Cambrian explosion, there was great diversity.〔 Four diagrams of evolutionary models〕 ==Extinctions== Periodic extinctions have temporarily reduced diversity, eliminating: * 2.4 billion years ago, many obligate anaerobes, in the Great Oxygenation Event; * 252 million years ago, the trilobites, in the Permian–Triassic extinction event; * 65 million years ago, the pterosaurs and nonavian dinosaurs, in the Cretaceous–Paleogene extinction event. * Currently, the Holocene extinction is occurring. Dates are approximate. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Timeline of the evolutionary history of life」の詳細全文を読む スポンサード リンク
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