RE: Ancient radiation levels were higher than today's levels

["Franta, Jaroslav" <frantaj@aecl.ca>]

		"the researchers estimated that
> 	radiation from these sources is now about one-half of what it was 4
> 	billion years ago, because many of these radioisotopes decayed in
> the
> 	intervening time."
> 
  ....I take it that includes the shorter-lived isotopes of uranium, such as
U235 -- what about longer-lived TRANS-uranics, like Pu-244 ? Are these
assumed to have vanished long BEFORE the formation of the solar system ?
(ie. ~ten half-lives, ~1GY)
And what about short-lived isotope deposition POST-formation of the planets
- from near-by supernova explosions - do we have any clue how many such
events there might have been & how much each one contributed ? What about
more common occurrences of Oklo-style radioisotope generators 4GY ago ?
Fascinating stuff !
Thanks,
Jaro
frantaj@aecl.ca
> ----------
> From: 	Jacobus, John (OD)[SMTP:JJacobus@exchange.nih.gov]
> Reply To: 	radsafe@romulus.ehs.uiuc.edu
> Sent: 	Wednesday, December 15, 1999 4:38 PM
> To: 	Multiple recipients of list
> Subject: 	Ancient radiation levels were higher than today's levels
> 
> For you reading pleasure from the American Institute of Physics.  Of
> course,
> this does not validate the idea of hormesis as being a derived from our
> biological past.  
> 
> -- John 
> 
> -----Original Message-----
> From: AIP listserver [mailto:physnews@aip.org] 
> Sent: December 10, 1999 3:37 PM
> To: physnews-mailing@aip.org
> Subject: update.461
> 
> 
> PHYSICS NEWS UPDATE                         
> The American Institute of Physics Bulletin of Physics News
> Number 461 December 10, 1999   by Phillip F. Schewe and Ben Stein
> 
> NATURALLY OCCURRING  RADIATION LEVELS ARE MUCH
> LOWER TODAY on Earth than when life first appeared, a new
> analysis has shown (Andrew Karam,716-275-1473,
> Andrew_Karam@URMC.Rochester.edu), suggesting that all living
> organisms--which have mutation-repair mechanisms very similar to
> those first developed by primordial life forms were once equipped to
> handle larger doses of background nuclear radiation than modern life
> forms.  Presently, humans receive a dose of about 360 millirems per
> year of radiation from natural sources, plus typically about 63 mrem/yr
> from anthropogenic sources.  Perhaps surprisingly, a major source
> (about 40 mrem/yr) of naturally occurring radiation is inside our
> bodies--in the form of potassium, a nutrient essential for many things
> such as generating signals between cells.  All natural sources of
> potassium contain some radioactive potassium-40 (K-40).  But life first
> began about 4 billion years ago--about 3 K-40 half-lives ago--meaning
> that the radiation dose from potassium today is about one-eighth of
> what it was 4 billion years ago.  Geologic sources of radiation (about
> 28 mrem/yr) include uranium, thorium, and potassium present in rocks
> and minerals in the earth's crust.  Studying published data of 1100
> rocks, and assuming that the continental crust had formed early (a
> scenario favored by the rock record), the researchers estimated that
> radiation from these sources is now about one-half of what it was 4
> billion years ago, because many of these radioisotopes decayed in the
> intervening time.  Not considered in the present study were cosmic
> sources (about 27 mrem/yr) and radon (typically about 200 mrem/yr);
> the authors are making these the subject of ongoing research.  (Karam
> and Leslie, Health Physics, December 1999.)
> 
> . . .
> 
> "If silence be good for the wise, how much better for fools. " 
> The Talmud
> 
> John Jacobus, MS
> Health Physicist
> National Institutes of Health
> Radiation Safety Branch, Building 21
> 21 Wilson Drive, MSC 6780
> Bethesda, MD  20892-6780
> Phone: 301-496-5774      Fax: 301-496-3544
> jjacobus@exchange.nih.gov (W)
> jenday@ix.netcom.com (H)
> ************************************************************************
> The RADSAFE Frequently Asked Questions list, archives and subscription
> information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html
> 
************************************************************************
The RADSAFE Frequently Asked Questions list, archives and subscription
information can be accessed at http://www.ehs.uiuc.edu/~rad/radsafe.html