The history of the UV radiation climate of the Earth – theoretical and space-based observations
In the Archean era (3.8–2.5 Ga ago) the Earth probably
lacked a protective ozone column. Using data obtained in
the Earth’s orbit on the inactivation of Bacillus subtilis
spores we quantitatively estimate the potential biological
effects of such an environment. We combine this practical
data with theoretical calculations to propose a history
of the potential UV stress on the surface of the Earth
over time. The data suggest that an effective ozone column
was established at a pO2 of ;5 3 1023 present atmospheric
level. The improvement in the UV environment
on the early Proterozoic Earth might have been a
much more rapid event than has previously been supposed,
with DNA damage rates dropping by two orders
of magnitude in the space of just a few tens of millions
of years. We postulate that a coupling between reduced
UV stress and increased pO2 production could have contributed toward a positive feedback in the production of
ozone in the early Proterozoic atmosphere. This would
contribute to the apparent rapidity of the oxidation
event. The data provide an evolutionary perspective on
present-day Antarctic ozone depletion.