Science Fair Project Encyclopedia
Eon (geology)
In general usage, an eon (also spelled Aeon) is a very long period of time. Geologists refer to an eon as the largest period of geologic time. For example, the Phanerozoic eon, which is about 550 million years long, covers the period of time during which animals with hard shells that fossilize well have been abundant.
An eon is composed of several eras, which in turn are composed of periods. We are currently in the Phanerozoic eon, the Cenozoic era and the Neogene period.
| Eon | Era | Period (mya = million of years ago) |
|---|---|---|
| Phanerozoic | Cenozoic | 66 mya to present day |
| Mesozoic | 245 mya - 66 mya | |
| Paleozoic | 570 mya - 245 mya | |
| Proterozoic | 2500 mya - 570 mya | |
| Archaean | 3800 mya - 2500 mya | |
| Hadean | 4550 mya - 3800 mya | |
The Hadean, Archaean and Proterozoic form what is informally called the Precambrian. This covers the four billion years of Earth history prior to the appearance of hardshelled animals.
References
Last updated: 05-10-2005 12:27:53
10-26-2009 08:16:03
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details
The contents of this article is licensed from www.wikipedia.org under the GNU Free Documentation License. Click here to see the transparent copy and copyright details