The effects of changing atmospheric oxygen concentrations and background radiation levels on radiogenic dna damage rates

Both background radiation levels and atmospheric oxygen concentrations have changed dramatically over the history of life on earth. Because oxygen has a strong modifying influence on radiogenic mutation rates, these factors m ust be considered jointly to determine changes in radiogenic mutation rates over time. Using accepted models that describe how both of these parameter s have changed through time, we find that radiogenic mutation rates in orga nisms have fluctuated between about 1.5 to 2.5 times current levels through most of the history of life. The results of this study have interesting im plications that may impact our understanding of how modern organisms respon d to radiation damage and of models that use molecular clocks to date speci es divergence times. It is also possible that changing oxygen levels have s erved to buffer mutation rate changes that result from changes in backgroun d radiation levels over time.