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

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

From: Brian_Gaulke@hc-sc.gc.ca [mailto:Brian_Gaulke@hc-sc.gc.ca]

Taking this to be true, the higher sensitivity amongst later "derived", more
complex organisms seems to imply a cost in maintaining the better
protection/repair mechanisms.  If there is such a cost, then why would the
less
complex organisms not have divested themselves of the unnecessary and costly
mechanisms now that environmental radiation levels are lower?

Brian R. Gaulke, CHP
===========================
Dear Brian -

What we're looking into now is occasional events ("periodic" implies a
regularity that is not present) with the capability of raising radiation
levels to much higher levels than normal.  A number of people have made
rather extravagant claims about supernovae and gamma ray bursts causing
periodic mass extinctions, but we tend to discount those.  However, there is
little doubt that a nearby supernova or a gamma ray burst anywhere in the
galaxy can raise background levels by a few hundred mrad (or a few mGy)
briefly and that this periodicity should be on the order of every few
million years.  In addition, nearby sun-like stars have been observed to
experience periodic "superflares" that emit a LOT of energy over a few days,
but the average time between such events is not yet well constrained.
Putting these together, it seems possible that, on an evolutionarily
significant time scale, rad levels may have been raised enough so that the
ability to address higher levels of radiation damage might not have been
lost.  In addition, any such events that deposited charged or uncharged
particles into the atmosphere would also create enhanced levels of
cosmogenic nuclide formation that would mix with seawater to circulate C-14
to all parts of the biosphere (with the possible exception of microbes
living deep in the crust, but they do not seem related to modern
multi-cellular life).  A lot of "maybe", "might", etc, but that's about all
we can tell for now.

Sincerely,

Andy
Andrew_Karam@urmc.rochester.edu

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