EARLY EARTH AND EARLY LIFE: AN EXTREME ENVIRONMENT AND EXTREMOPHILES ― APPLICATION TO THE SEARCH FOR LIFE ON MARS

摘要

The early Earth was an extreme environment compared to the present day Earth: oceans with probably higher salinity and lower Ph, evaporitic conditions in the littoral environment, temperatures 70-80°C, little or no O_2 in the atmosphere, pervasive volcanism and hydrothermal activity, and peak bolide activity between 4.0-3.85 b.y. ago. The oldest fossil evidence from 3.45 b.y. old sediments shows that life was widespread and thriving in and around hydrothermal vents and in evaporitic, littoral environments, exposed to high UV radiation. Given thse conditions, life must have been extremophile by definition. Although there are strong dissimilarities between the geological evolution of early Mars and early Earth, from a microbial point of view, the environmental conditions on both planets were very similar, although the wider range in temperatures on Mars may have made a wider diversity possible. Early Earth and early life therefore represent an excellent analogue for the study of potential early Martian life.