  The emergence of life on the Earth has required a prior organic chemistry
leading to the formation of prebiotic molecules. The origin and the evolution
of the organic matter on the early Earth is not yet firmly understood. Several
hypothesis, possibly complementary, are considered. They can be divided in two
categories: endogenous and exogenous sources. In this work we investigate the
contribution of a specific endogenous source: the organic chemistry occurring
in the ionosphere of the early Earth where the significant VUV contribution of
the young Sun involved an efficient formation of reactive species. We address
the issue whether this chemistry can lead to the formation of complex organic
compounds with CO2 as only source of carbon in an early atmosphere made of N2,
CO2 and H2, by mimicking experimentally this type of chemistry using a low
pressure plasma reactor. By analyzing the gaseous phase composition, we
strictly identified the formation of H2O, NH3, N2O and C2N2. The formation of a
solid organic phase is also observed, confirming the possibility to trigger
organic chemistry in the upper atmosphere of the early Earth. The
identification of Nitrogen-bearing chemical functions in the solid highlights
the possibility for an efficient ionospheric chemistry to provide prebiotic
material on the early Earth.

Earth and Planetary Astrophysics