Solar X-ray and UV radiation at Earth’s surface 4-3.5 billion years ago.
Minor atmospheric components, such as methane, ozone, water vapor, etc., have only negligible effects, but changes in CO2 concentration can cause large differences in surface flux. Differences due to variability in solar emission are small compared to this. In all cases surface radiation levels on the Archean Earth were several orders of magnitude higher in the 200-300 nm wavelength range than current levels in this range. That means that any form of life that might have been present at Earth’s surface 4-3.5 Ga, must have been exposed to much higher quantities of damaging radiation than at present.
It can be concluded from our results that any life that would have evolved at Earth’s surface 4-3.5 Ga, would have been exposed to damaging radiation fluxes (figure 6). It would not only have experienced higher levels of solar radiation in general, but also more damaging (shorter wavelength) radiation than now, and therefore it is questionable if life would have been sustainable at all at Earth’s surface in the Archean. . It may be more realistic to envisage an origin of life in an environment where it was shielded from the harmful radiation, for instance in the deep sea. This is sometimes called the Berkner-Marshall hypothesis [Berkner and Marshall, 1965].