Abstract
I review the relative importance of internal and external sources of prebiotic molecules on Earth at the time of life's origin μ3.7Gyr ago. The efficiency ofsynthesis in the Earth's atmosphere was critically dependent on its oxidation state. If the early atmosphere was non-reducing and CO2-dominated, external delivery might havebeen the dominant source. Interplanetary dust grains and micrometeorites currently deliver carbonaceous matter to the Earth's surface at a rate of μ 3 × 105kg/yr(equivalent to a biomass in μ2Gyr), but this may havebeen as high as 5 × 107kg/yr (a biomass in onlyμ10Myr) during the epoch of late bombardment. Much ofthe incoming material is in the form of chemically inactive kerogens and amorphous carbon; but if the Earth once had a dense (μ10-bar) atmosphere, small comets rich in avariety of prebiotic molecules may have been sufficiently air-braked to land non-destructively. Lingering uncertainties regarding the impact history of the Earth and the density and composition of its early atmosphere limit our ability to draw firm conclusions.
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Whittet, D.C.B. IS EXTRATERRESTRIAL ORGANIC MATTER RELEVANT TO THE ORIGIN OF LIFE ON EARTH?. Orig Life Evol Biosph 27, 249–262 (1997). https://doi.org/10.1023/A:1006534500363
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DOI: https://doi.org/10.1023/A:1006534500363