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Geology : Paleontology
THE RELATIVE TIME SCALE
Long before geologists had the means to recognize and express
time in numbers of years before the present, they developed the geologic time
scale. This time scale was developed gradually, mostly in Europe, over the
eighteenth and nineteenth centuries. Earth's history is subdivided into eons,
which are subdivided into eras, which are subdivided into periods, which are
subdivided into epochs. The names of these subdivisions, like Paleozoic or
Cenozoic, may look daunting, but to the geologist there are clues in some of the
words. For example, zoic refers to animal life, and
paleo means ancient, meso means middle, and
ceno means recent. So the relative order of the three youngest
eras, first Paleoozoic, then Mesozoic, then
Cenoozoic, is straightforward.
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Fossils, Rocks, and Time
By Lucy E. Edwards and John Pojeta, Jr.
Contents & Introduction
Putting Events in Order
The Relative Time Scale
Rocks and Layers
Fossils and Rocks
The Numeric Time Scale
The relative geologic time scale. The oldest time interval is at the bottom and the youngest is at the top.
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