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Re: geologic periods
> On Tue, 10 Jan 1995, Tom Holtz wrote:
> The Cretaceous is THE longest formal period in Earth's history. It
> million years longer than the whole of the Cenozoic. Dinosaur
> averaged only some 3-6 million years or so.
> At the level of geologic period, the Cambrian was longer by several
> of years (approximately 90 vs approximately 75). Obviously the
> is a formal period of time and is the longest formal time increment.
Here is the most up to date (1989) details of the geological column
and the lengths of the Periods in millions of years.
'Quaternary' = 1.64
Neogene = 21.7
Paleogene = 41.7
Cretaceous = 81.0
Jurassic = 62
Triassic = 37
Permian = 45
Carboniferous = 73 (Pennsylvanian = 33; Mississippian = 40)
Devonian = 46
Silurian = 31
Ordovician = 71
Cambrian = 60
Vendian = 40
As for the Precambrian......it is not a period, but a time before the
Cambrian. The Proterozoic Eon is a subdivision of the Precambrian
and is in turn subdivided into the Neo-, Meso- and Palaeoproterozoic
Eras which last a total of 1,930 million years. These are subdivided
intoPeriods that can last for a couple of hundred million years or so
each and, therefore, could be considered as being the longest
Periods. However, I presume that Tom was referring to the longest
Period in the Phanerozoic Eon.
Curator of Palaeontology
University of Glasgow
Mountains are found in erogenous zones.
(Geological Howlers - ed. WDI Rolfe)