Eon

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The first number in the parentheses refers to the number of eons. It is parallel to the eon in the Geologic Time Scale (GTS) in that it is also the largest measure of time.  In the GTS’s case, the geologic eon ranges in length from 500 million to 2 billion years. The lengths of terms in the GTS such as (geologic) eons are based on stratigraphy and Earth history, not time.

But the length of an Eon in the Earth Epic Calendar (which can also be called a “Calendar Eon” to distinguish from the GTS) is a fixed period of time–in this case, 250 million years.

In addition to being the largest measure of time, the Eon also happens to coincide somewhat closely to a significant time in the Earth’s history. Dinosaurs first appeared on Earth between 243 million and 231 years ago. Also the Cambrian Explosion, in which most of the major animal phyla that exist today first appeared was a little more than two Eons ago.

Another interesting coincidence is that the length of an Eon on this calendar is the upper estimate of what is known as a Galactic Year That is about the length of time that our Sun takes to orbit around the Milky Way galaxy.

The Earth is approximately 4.54 billion years old,  give or take 40 million years. If we divided 4.54 billion by 250 million, we could then say that the earth is 18.16 eons old. As such, we say that we are in Eon 18.

This unit of time is helpful in understanding Earth history. It is revealing that the time period between the present and the advent of the dinosaurs constitutes less than one-eighteenth of the entire history of Earth. See how much better we understand Earth history already?

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