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RE: " we're evolved for radiation " - geophysicist on pole revers als
Jaro,
My comments are based on my disbelief that the magnetic field of the earth
has any influence of the radiation we receive from space, whether it is
ionizing or UV. I was wonder why the comment was made "we're evolved for
radiation" in the context of the article.
By the way, I believe that Mars lacks a magnetic field. Of course, we do
not know if life exist there, so maybe a magnetic field is necessary.
-- John
John Jacobus, MS
Certified Health Physicist
3050 Traymore Lane
Bowie, MD 20715-2024
E-mail: jenday1@email.msn.com (H)
-----Original Message-----
From: Franta, Jaroslav [mailto:frantaj@AECL.CA]
Sent: Monday, November 04, 2002 12:36 PM
To: Radsafe (E-mail)
Subject: RE: " we're evolved for radiation " - geophysicist on pole revers
als
-----Original Message-----
From: Jacobus, John (NIH/OD/ORS) [mailto:jacobusj@ors.od.nih.gov]
Sent: Monday November 04, 2002 11:37 AM
To: RADSAFE
Subject: RE: " we're evolved for radiation " - geophysicist on pole revers
als
Jaro,
Thanks for putting a "date" on the last magnetic field reversal. I always
assumed that the atmosphere was the source of shielding for life on earth..
That is why any life on Mars would be primitive at best, and why single cell
creatures were the only life form on Earth for so long..
-- John
Sorry, but I don't follow your reasoning.
Over millions of years, the main agent of the mutations responsible for
biological evolution is radiation (the last polarity flip was less than a
million years ago).
So life is liable to remain primitive in the absence of radiation, not its
presence ("we wouldn't be here if it weren't for radiation").
What the atmosphere shields us from is UV radiation, mainly by the ozone
component.
The atmosphere of Mars is very thin and lacks the UV-protective ozone layer,
thus killing any life on the surface.
However, according to some estimates, even on the Earth, most of the total
biomass of the planet resides underground - including deep underground, up
to several kilometers - in the form of single-celled thermophilic life
forms. That those haven't evolved (much, except for the amazing radiodurans
bacteria) is something of a curiosity, because over long periods (thousands
of years, when in the dormant state) they will get a huge cumulative dose
from geological NORMs.
I haven't seen any data on Martian polarity reversals. Much more surface
exploration will have to be done before such data is obtained (may not exist
if Mars has no plate tectonics), or information about possible subsurface
microbial life. It is known however, that early in its history Mars had
large oceans of water, similar to the earth.
There is also a high probability (read certainty) that even if indigenous
life did not evolve on Mars, microbial life from earth would have
contaminated its neighbour by way of meteoritic impact ejecta transfer (and
vice-versa, from Mars to Earth - we could be descendants of Martians :-).
Why were single cell creatures the only life form on Earth for so long ?
Good question. But I don't see an answer in any of the above. I believe that
current exobilogical theory holds that its just a matter of extremely low
probability for evolving multicellular life.
Jaro
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