From: LARRY KLAES (ljk4@msn.com)
Date: Mon Jul 29 2002 - 17:22:03 PDT
PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 599 July 24, 2002 by Phillip F. Schewe, Ben Stein, and
James Riordon
ICE AGES AND SPIRAL ARMS. New research suggests that ice
age epochs on the earth may result from our solar system's trek
through the spiral arms of the Milky Way. Nir Shaviv
(shaviv@phys.huji.ac.il, +972-54-738555), of the University of
Toronto and Jerusalem's Hebrew University bases this hypothesis
on correlations he has found between apparent changes in the flux
of cosmic rays reaching the earth and geological evidence for
major ice ages in the past billion years. Galactic spiral arms are not
permanent, rigid fixtures; rather they are transient and result from
density ripples traveling around the galaxy. Many massive stars
form in the wake of the density waves and later explode as
supernovae, which are a primary source of cosmic rays. It seems
reasonable to expect our planet to receive more cosmic rays when
it is near the supernovae in a major spiral arm. If there is a
connection between cosmic ray flux and climate (see Update 401),
past ice ages should correlate with the solar system's location
relative to the traveling spiral arms.
One of the challenges in making the climatic connection is
finding records of cosmic ray flux over past eons. Shaviv deduced
the earth's exposure to cosmic rays by considering the cosmic ray
exposure of 42 iron meteorites. The meteorite record seems to
indicate that the cosmic ray flux varies with a period of about 143
million years, which correlates well with both the geological
records of ice age epochs and the solar system's location relative to
the spiral arms. Our current position in the minor Orion spiral arm
should lead to cosmic ray fluxes about half of what we would
receive in a major spiral arm. Shaviv's model places us in the wake
of a major ice age epoch, and is consistent with the global
temperatures that we are now experiencing. Shaviv points out that
the weakest link in his proposal is uncertainties in the extent and
timing of glacial periods indicative of ice age epochs, and that
further geological research is necessary to confirm that galactic
spiral arms affect our climate. (Nir J. Shaviv, Physical Review
Letters, 29 July 2002)
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