Cs. Cockell, BIOLOGICAL EFFECTS OF HIGH ULTRAVIOLET-RADIATION ON EARLY EARTH - A THEORETICAL EVALUATION, Journal of theoretical biology, 193(4), 1998, pp. 717-729
The surface of early Earth was exposed to both UVC radiation (< 280 nm
) and higher doses of UVB (280-315 nm) compared with the surface of pr
esent day Earth. The degree to which this radiation environment acted
as a selection pressure on organisms and biological systems has rarely
been theoretically examined with respect to the biologially effective
irradiances that ancient organisms would receive. Here action spectra
for DNA inactivation and isolated chloroplast inhibition are used to
estimate biologically effective irradiances on archean Earth. Comparis
ons are made with present day Earth. The theoretical estimations on th
e UV radiation screening required to protect DNA on archean Earth comp
are well with field and laboratory observations on protection strategi
es found in present day microbial communities. They suggest that many
physical and biological methods may have been effective and would have
allowed for the radiation of life even under the high UV radiation re
gimes of archean Earth. Such strategies would also have provided;effec
tive reduction of photoinhibition by UV radiation. The data also sugge
st that the UV regime on the surface of Mars is not a life limiting fa
ctor per se, although other environmental factors such as desiccation
and low temperatures may contribute towards the apparent lack of a sur
face biota. (C) 1998 Academic Press.