Cryptozoic Breakdown?

No, “Cryptozoic Breakdown” is not the answer to “album name?” à la the Dave-Barryesque “band name” catchphrase around here. :wink:

Here’s my question: Historical geology recognizes the Paleozoic, Mesozoic, and Cenozoic Eras, each of which are broken down into periods (Cambrian, Devonian, Jurassic, Quaternary, etc.), and the periods into epochs.

But together they constitute only the last 560 million years of the 4.6 billion years of earth’s history, the Phanerozoic Eon.

All the four billion previous years are lumped together as the Cryptozoic Eon or, more vaguely, Pre-Cambrian time.

When I was growing up, this was broken into the Proterozoic and Archeozoic Eras, each of which was in turn divided at least two periods. My recent reading says that this is accurate only for the Western Great Lakes, and probably doesn’t represent an accurate reflection of precambrian time in general.

So is there any standard, generally accepted breakdown into eras, periods, and such used by reputable historical geologists for the Cryptozoic?

How about the Geological Society of America: GSA Geologic Time Scale

I don’t know much 'bout geology, but this site lists a couple different breakdowns of the Cryptozoic, aka Pre-Cambrian.

The first is similar to what you mentioned: it is broken down into the Proterozoic (570 mya - 2500 mya), the Archaeon (2500 mya - 3800 mya) and the Hadeon (> 3800 mya) eras. The Proterozoic appears to be broken down a bit more finely (perhaps because recent fossil finds have allowed better resolution). So, we have the Neoproterozoic (540 mya - 900 mya), the Mesoproterozoic (900 mya - 1600 mya) and the Paleoproterozoic (1600 mya - 2500 mya).

Here is a nice one, in pretty colors, too.

That’s the nice thing about standards: There’s so many to choose from.


Hmm… some words on the Precambrian geologic time scale and the associated terminology.

The first time scale on the link given by Darwin’s Finch is definitely outdated; the second one is a little closer to the mark, but still not quite right. The GSA time scale is also a little bit off; funny, I never noticed that before. (The age of the Precambrian-Cambrian boundary is now set at 543 My +/- a few hundred thousand years.)

The first table in Q.E.D.'s link is the one to go with, as it has been proposed by the International Union of Geological Sciences, International Commission on Stratigraphy. This is the governing body that makes decisions on the names of time divisions, as well as setting the age boundaries for all. It is important to realize, though, that the period names for Proterozoic eras are only proposed names, and as such are rarely, if ever, used. There is currently a working group that has, as its goal, the formal definition (through selection of a stratigraphic type section in the field) and naming of the youngest Neoproterozoic period. This is actually as much more political process than one might think, with proponents of potential type sections in different countries (such as Canada, Australia, China, Russia) lobbying very hard for their own. The working group has been at it for more than 10 years now… and EACH proposed period of Proterozoic will have to go through the same process, so you can just imagine how long it will take to formalize the whole time scale. :wink:

For folks working at this part of the time scale (reputable or not :wink: ), “Precambrian” is a catch-all term for any time prior to the beginning of the Phanerozoic eon. Neoproterozoic (1000-543 Ma), Mesoproterozoic (1600-1000 Ma) and Paleoproterozoic (2500-1600 Ma) eras are all commonly used. So is Archean eon for 4500-2500 Ma (although the era-level subdivisions of the Archean are rarely used). “Cryptozoic” is an older term that is no longer used.

Hope this helps.