paleo-health physics

["Karam, Andrew" <Andrew_Karam@URMC.Rochester.edu>]

-----Original Message-----
From: Harald Weiss [mailto:weiss@ki.comcity.de]
Well, not yet ...

A while ago I had a short discussion with Andrew on one of my favourite
hypothesis: Having observed out of studies cited in the literature that
lower organised (= older) forms of life show a lower sensitivity against
radiation, I speculated on the possibility that the specific sensitivity
might have been adequate to the level of radiation prevailing at the
time when the species derived. (Just applied Darwinism ...)

===================

There are two major things Steve and I are considering in this arena.
First, supernovae and gamma ray bursts occur intermittently and have the
capability of briefly elevating radiation exposure significantly.  What
we're looking at first is the dose from all sources in these events at
varying distances and, after that, the mean time between events at those
distances.  It looks as though, every few million years, Earth would receive
about 100 mrem (1 mSv) in gamma radiation from one of these sources.
Contributions from charged particles, cosmic ray air showers, and so forth
will be more difficult to ascertain.

Second, solar luminosity has steadily increased with time (about 50%
increase), solar activity has changed, and sun-like stars have been
periodically noted to undergo "superflare" events which dump a lot of energy
into their immediate environment in a short period of time.  We haven't
started looking at these yet in any detail, but they must be considered.

A side note that is of peripheral interest is that we have recently
completed looking at the effects of changing background radiation levels on
rates of evolution over time.  Molecular clock models for dating the
divergence of species almost invariably over-predict these divergences when
compared to the fossil record.  In other words, a molecular clock will
indicate two species diverged 400 million years ago but the fossil record
indicates this event happened "only" 300 million years ago.  However, if you
apply a correction to the "straight-line" models used in molecular clock
research that is based on the decay of K-40 (or the accumulation of K-40 if
we're going backwards in time) then the molecular clock comes into much
closer agreement with the fossil record.  Unfortunately, while we've given
some journals the opportunity to publish this result, none have taken us up
on this offer yet.  But we're still trying....

We are speculating that these events, plus other less important ones, may
occur frequently enough to provide a steady selection pressure for more
active mutation repair mechanisms.  We hope to have some more quantitative
answers in another few years.  Unfortunately, this research is something
that I have to do in the evenings, after my "real" job of RSO is over for
the day and after I tuck my son in for the night.  

My apologies for a rather lengthy reply to a really short comment.

Andy

Andrew Karam, CHP              (716) 275-1473 (voice)
Radiation Safety Officer       (716) 275-3781 (office)
University of Rochester        (716) 256-0365 (fax)
601 Elmwood Ave. Box HPH       Rochester, NY  14642

Andrew_Karam@URMC.Rochester.edu
http://Intranet.urmc.rochester.edu/RadiationSafety

We cannot prove that those are in error who tell us that society has
reached a turning point, that we have seen our best days.  But so said
all before us, and with just as much apparent reason.  On what principle
is it that, when we see nothing but improvement behind us, we are to
expect nothing but deterioration before us?    Lord Thomas B. Macaulay,
1830
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