LAUSR

Earth’s early surface environment had great influence on the origin of life through formation of its building blocks. From geological and geochemical evidence, the Earth’s atmosphere and oceans appear to have existed since a very early period in the Earth’s history. Recent models of planet formation suggest that a significant amount of volatile elements that formed the Earth’s atmosphere and oceans was supplied to Earth during its formation. This very early supply of volatile elements is consistent with recent detailed analysis of isotopic compositions of terrestrial and extraterrestrial materials. Chemical equilibrium calculations showed that the volatile elements degassed by accreting bodies contained some reduced gases. Moreover, metallic iron in differentiated bodies accreting on Earth played an important role in reducing the surface environment through producing abundant hydrogen molecules from oceans. These recent studies indicate that the Earth’s early atmosphere was more reduced than previously thought, which would be an advantage for formation of the building blocks of life. After Earth’s formation, late accretion caused impact erosion and replacement of the pre-existing atmosphere and oceans. However, due to the complicated phenomena of impact erosion, it is difficult to make an accurate estimate of the loss and replacement of the atmosphere at present.