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The geological time scale – eons, eras, periods and epochs.

November 28, 2012

The geological time scale has always fascinated, I think in part, because the duration of human history is such a minuscule fraction of the some 4 and half billion year history of the Earth, or indeed the history of life itself. The figure at the left illustrates this somewhat. It shows the geological time scale with different temporal divisions at increasingly finer scales from eons on the left through to epochs on the extreme right. The dates are approximate as there is some discussion over these. The Hadean is often not considered a formal eon nor is the division between the Archean and Hadean particularly precise. The Quaternary is divided up into Pleistocene and Holocene, the latter of which began approximately 12,000 years ago and is comprised of the thin rectangle above the Pleistocene in the temporal sequence of Epochs to the right of this figure. PH = Phanerozoic. CE = Cenozoic. This figure was modified from Gradstein et al. (2004) and from information contained on the British Geological Survey web site (click on the image to see a larger version).

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