The Clock of Eras is a graphic aid to help us visualize geologic time. It is nearly impossible for the human mind to comprehend the amount of time that it has taken for the Earth to develop to its present state, yet we try to imagine each stage of its unfolding and the time that passed during each phase of development.
Just a note here: The original Clock of Eras was developed about 100 years ago. Our understanding of geologic time has come a long way. To get to the point the only true eras on the clock now are the Paleozoic, Mesozoic, and Cenozoic. The Proterozoic and Archaean are now termed Eons and the Hadean is neither era nor eon. The geologic time scale was created based on layers of rock. During the Hadean Time the earth was molten, eventually cooling to a solid crust. However no traces of this original crust have been found. So since there are no rocks to study the designation Hadean Time is used. Still the name of the clock has not changed, nor has its usefulness in picturing the vastness of time in the earth's history.
The Clock of Eras uses the
analogy of a circular clock to represent the development of our planet
in geologic time. One can see at a glance the relative time lengths of
each major geologic era.
So how does this Clock work? The Clock represents geologic time on the
Earth since its birth to the present, from the initial events that
brought about the formation up to now. Each hour represents
approximately 375 million years.
We can’t take credit for the idea of this Clock. It is a concept that was developed in Montessori Education. The colors as used in the Montessori clock relate to the location of the life that was present during the time. So the Paleozoic Era is blue because life was primarily in the seas, the Mesozoic is brown because life moved to the land, and the Cenozoic is green because of the fresh new life: the mammals.
The Clock of Eras has been modified several times already and will continue to change over time as scientists learn more and more information through their research and discovery.
Click on the links below the clock for a description of each time period.
The first period of the clock of eras is the Hadean
A description of the Archean
A description of the Proterozoic Era
A description of the Paleozoic Era
A description of the Mesozoic Era
A description of the Cenozoic Era.
A clock of eras chart.Click here for a printable version.
A blank or non-colored chart Click here for a printable version
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Geologic Time Geologic Time LineProterozoic Era