From: swf@teradata.com (Stanley Friesen)
Newsgroups: talk.origins
Subject: Re: Age of Earth and Origin of Life
Date: 28 Jul 92 18:39:36 GMT
Reply-To: swf@tdat.teradata.com (Stanley Friesen)
Followup-To: talk.origins,bionet.molbio.evolution
Organization: NCR Teradata Database Business Unit

In article <1992Jul28.004905.7322@bronze.ucs.indiana.edu> jlogsdon@sunflower.bio.indiana.edu (John Logsdon) writes:
|
|I am wondering; what serious values have been proposed for the age of earth?
|In casual converstion, I usually hear values ca. 4.5 Billion years.

This is really the only currently used figure.

|In a quick check of a few paleobotany texts (all I have at my immediate
|disposal) this is close to what they cite in their "geological columns." 
|In a nutshell,on which isotopes are these based and what statistical errors 
|correspond to these measures? 

It is based on many different lines of evidence, including, but not
limited to, Potassium-Argon dating, fision track dating, correlation
analysis, meteorite dating, lunar rock dating, and so on.

The value is well determined, the maximum possible error is about +/-0.2 BY

|In a recent paper in  _Science_ (v257: 232-235, 10 July 1992), the authors
|claim to have found fossil eukaryotic algae that are ca. 2.1 BY old. This 
|is striking to me because this lineage likely represents a fairly derived
|eukaryotic lineage itself.

Perhaps, perhaps not.  "Algae" is an ambiguous term, it simply refers to
various photosynthetic protists.  And, on top of that, it is not possible
to tell if the fossil 'euks' were actually photosynthetic.  Thus little
can really be said about the relationships of these fossils.

|  In fact, Archaezoa (euks with out mitochondria, ie:
|_Giardia_, that wonderful intestinal parasite) are probably MUCH older than 
|the Algae they found (_Grypania_).  Given this and that the root of the 
|tree of life is EVEN DEEPER [either between eubacteria and 
|archaebacteria+eukaryotes, OR between two groups of archaes (see _Science_ 
|v257: 74-76, 3 July 1992)], this seems to put "life" (ie: the common ancestor 
|of all life: the "progenote") fairly ancient, perhaps ca. 3.5 BYA.  

There are known 'prokaryote' fossils from about that age any way, so you
need not deduce it from other facts.

Also, the oldest known in-situ metamorphic rocks show isotope profiles
suggestive of biotic processes.  These are about 3.8 to 3.9 BYA.
Since all older rocks have been heavily reworked, life may well have
been around even longer.  (This reworking does not effect dating of
the Earth - even small intact inclusions can be used for that purpose)

|This, as I read it, apparent ca. ONE billion year gap between the Earth's
|origin and the origin of life is the impetus of this post. From a VERY
|naive point of view, this doesn't seem very long. If in fact there
|is significant statistical error associated with the Age of the Earth, or the
|Dating of the fossils in question for that matter, perhaps there is a longer
|time period between the Earth origin and Life origin. If not, are there any
|problems with such an apparently limited time frame for evolution of life
|theories? 

It may be even less than that, especially after you allow for the Earth
to cool down enough to support life.  We are talking perhaps 500 *million*
years from liquid water to first life.


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