BIOLOGICAL EFFECTS OF HIGH ULTRAVIOLET-RADIATION ON EARLY EARTH - A THEORETICAL EVALUATION

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.