Ancient radiation levels were higher than today's levels

["Jacobus, John (OD)" <JJacobus@exchange.nih.gov>]

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)
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