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Sunday, March 25, 2007

NOW ITS going to be geological time scale about the past eras and the present era !
first let me tell u guys what is geological time scale

The Geological Time Scale
Scientists divide the Earth into a number of periods - the "geological time scale according to the rock types and sort of fossils found in each one. These divisions are pretty arbitrary, like any man-made divisions, but they at least can serve as useful labels. So the Paleozoic, the era of "ancient life" is characterized by fossils of invertebrates, primitive tetrapods, etc; the Mesozoic or era of "middle life", by fossils of dinosaurs etc, and the Cenozoic or era of "recent life" by mammals and modern plants and invertebrates.
These eras are divided into periods, the system of which was established by the end of the last century. The periods are in turn divided into epochs, and the epochs are divided into ages called ages.
Scientists know these periods lasted for millions of years, because they can date them with a fair degree of accuracy according to the amount of radioactivity that occurs in the rocks.
The geological time scale can also be used to define the major stages in the history of life on Earth. Often each era ends with a major extinction, which eliminates the dominant life forms of the time and paves the way for newcomers

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