Simulation of planetary UV radiation climate on the example of the early Earth

Abstract

Solar UV radiation is a dynamic driving force of organic chemical evolution. However, it may have severe constraints in biological evolution, for instance in the early history of life on Earth, before atmospheric evolution of a protective ozone layer. Today, the full spectrum of solar UV radiation is experienced only in space. In the experiment RD-UVRAD on D-2 the biological response to solar UV as a function of ozone concentrations down to very low values was investigated. Biofilms, biological UV dosimeters, were exposed to the extraterrestrial solar radiation on one of the two exposure trays mounted on the User Support Structure (USS) with free access to space. Different cut-off filters, which exclude UV of short wavelengths, and neutral density filters were used. After the flight the biofilms were developed and analyzed on ground. As a result a strong correlation between the increase in biologically effective UV radiation with decreasing (simulated) ozone concentrations was observed. Without any ozone the solar UV radiation is about three orders of magnitude more effective than today on Earth. This space experiment resulted in new insights in the environmental conditions of life on the early Earth and in the deleterious biological consequences of future stratospheric ozone depletion.