Author: Tom HendricksTom Hendricks Date: Mar 2, 2008 11:09
Some ideas from:
The ultraviolet history of the terrestrial planets Ð implications
for biological evolution
Charles S. Cockell*,1
M/S 239-20, NASA Ames Research Center, Moett Field, CA 94035-1000,
USA
Received 24 June 1999; accepted 27 August 1999
'Using observations of stars, Zahnle and Walker provide spectra for
the sun at 3.5 Ga and present-day.
The 25%% reduction in luminosity corresponds to an approximately 35%%
reduction in the biologically im-
portant UV range (Zahnle and Walker, 1982). Solar
luminosity was assumed to increase linearly over time to present-day
values. '
UV was lower at the start - though I've heard that the new sun (4.5?)
was higher UV.
So it may have started out high, and come down a bit. Then increased
till the ozone shield developed.
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