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Geologic Time Geologists and paleontologists measure the Age of the Earth and the History of Life in millions and billions of years. The entire history of humankind is but a blink of an eye next to the vastness of geological time. Click on the table at right to view the different Ages of the Earth |
HISTORY OF EARTH |
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Earth History Video |
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For this reason a special kind of "calendar" is required; one that measures not weeks, months or years, but millions, tens of millions and hundreds of millions of years. This is the Geological Time-Scale (above). The Geologic Time-Scale is divided into units. From the largest to smallest these are: Eons, Eras, Periods and Epochs. Each of these time periods had different conditions and unique ecosystems. Their beginning and end are often marked by some event such as a mass extinction, the appearance of new life, a change in the rocks' magnetic signature, or by human convention. The oldest eons, eras and periods are at the bottom and the youngest at the top. The reason for this convention is that the Time-Scale symbolically represents the layers of sedimentary rocks that make up the Earth's crust. The earlier, older layers were deposited first, and the later, younger ones on top of them. For this reason the time units also refer to layers of rock -- for instance, dinosaurs lived during the Jurassic Period, and dinosaur fossils can be found in Jurassic rocks. The distance from the present to the past
is usually measured as "millions of year ago" (mya)
or "billions of years ago" (bya). Click
on the Time-Scale above to visit the different Ages of the Earth. |
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Corey Zak - Corzak Interactive |
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