Abstract
A model for the survival of the amino acid content in micrometeorites and its possible transformations upon atmospheric entry is described. Since any organic species released in the atmosphere at high altitudes would exhibit a limited lifetime with respect to the typical timescale for atmospheric mixing (due to the substantial radiation field of the early Sun), only the organic content inside the meteorites could have contributed to prebiotic chemistry. It is thus important to determine both the amino acid loss from meteorites, due to both degassing and chemical degradation, and the extent of the chemical transformation of amino acids subjected to the increased temperature due to friction with the atmosphere. According to the interplay between the potential energy barrier and the pre-exponential factor in rate coefficients, either diffusion or chemical processing might be the dominant process following the rising temperature upon atmospheric entry. The possibility of the elimination of water from glycine to form aminoketene, or CO2 to form methylamine, ultimately driven by gravitational energy, was examined along with the more conventional formation of a peptide bond between two glycine units to afford Gly–Gly. While retention, degassing, and decarboxylation are the fastest processes, each dominating in different ranges of the initial velocity and radius, the formation of either Gly–Gly from bimolecular water elimination or aminoketene from unimolecular water elimination appears to be negligible.
Highlights
One of the hypotheses concerning the origin of complex organic chemistry on the early Earth entails the continuous supply of small organic molecules in the flux of micrometeorites and interplanetary dust particles
If micrometeorites were the carriers of this source, it is crucial that the load of organic species would survive the atmospheric heating and reach the Earth surface [6]
When the temperature equals 744.4 K decarboxylation attains the same rate as degassing, and after that time, it dominates all rates. This result is in agreement with the findings of [12] that found no evidence for the formation of dipeptides or diketopiperazines during the sublimation of amino acids from the Murchison meteorite
Summary
One of the hypotheses concerning the origin of complex organic chemistry on the early Earth entails the continuous supply of small organic molecules in the flux of micrometeorites and interplanetary dust particles. Leucine was shown to withstand solar radiation for three months when embedded in a 5 μm layer of montmorillonite clay [7], the delivery of the organic species directly to the atmosphere at high altitudes would subject the organics to the substantial UV radiation field of the early Sun, limiting the lifetime of the organic species to less than the typical timescale for atmospheric mixing [8]
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