The role of primordial atmosphere composition in organic matter delivery to early Earth

A model of the atmospheric entry of sub-mm grains is employed to evaluate the effect of the chemical composition of the primordial Earth's atmosphere on the grain heating, in the context of organic matter delivery. Calculations are performed with spherical, uniform grains of forsterite/fayalite composition as well with the recently proposed white soft mineral (WSM) grains. Different hypotheses on primordial atmosphere composition affect the scale height and the energy transfer. The present work shows that: the total gas budget of the atmosphere is not highly relevant as far as the determination of the heating associated with slowing to subsonic speed is concerned; accordingly, light components (which are expected to be present in a primordial atmosphere and more abundant in the upper one) may be the primary ones in the evaluation of momentum and heat transfer in such scenarios. Strong reduced heating is obtained in the case of an upper atmosphere rich in light components, showing that the composition of the primordial Earth atmosphere may represent the key issue in the delivery of thermolabile organic matter enclosed in sub-mm extraterrestrial grains.