Flash heating on the early Earth.

It has been suggested that very large impact events (approximately 500 km diameter impactors) sterilized the surface of the young Earth by producing enough rock vapor to boil the oceans. Here, we consider surface heating due to smaller impactors, and demonstrate that surface temperatures conductive to organic synthesis resulted. In particular, we focus on the synthesis of thermal peptides. Previously, laboratory experiments have demonstrated that dry heating a mixture of amino acids containing excess Asp, Glu, or Lys to temperatures approximately 170 degrees C for approximately 2 hours yields polypeptides. It has been argued that such temperature conditions would not have been available on the early Earth. Here we demonstrate, by analogy with the K/T impact, that the requisite temperatures are achieved on sand surfaces during the atmospheric reentry of fine ejecta particles produced by impacts of bolides approximately 10-20 km in diameter, assuming approximately 1-100 PAL CO2. Impactors of this size struck the Earth with a frequency of approximately 1 per 10(4)-10(5) y at 4.2 Ga. Smaller bolides produced negligible global surface heating, whereas bolides > 30 km in diameter yielded solid surface temperatures > 1000 K, high enough to pyrolyze amino acids and other organic compounds. Thus, peptide formation would have occurred globally for a relatively narrow range of bolide sizes.