How comet impacts may have formed the building blocks of early life
Proteins form the machinery of life: they catalyze the chemical reactions that allow organisms to gain energy and reproduce. A study presented at the 2015 Goldschmidt conference shows how oligopeptides, the precusors of proteins, might have been formed when comets impacted the Earth nearly 4 billion years ago.
Comets are believed to contain substantial quantities of amino acids, the building blocks of proteins. To see how those amino acids could combine into larger oligopeptides, Haruna Sugahara and her Ph.D. advisor, Koichi Mimura, fired mixtures of amino acids, ice, and silicate minerals at high speeds into a target that had been cooled to nearly 200 degrees Celcius below zero. The energy provided by the impact caused the amino acids to form into short chains, up to three amino acids long, known as oligopeptides. Crucially, these oligopeptides formed linear chains rather than closed circles, meaning that they would be available for futher reactions to create more of the building blocks of life. Sugahara’s use of a cold target was critical: previous experiments at room temperature resulted in about 50% cyclic dipeptides, which were too stable to be likely to react futher.
How many oligopeptides could comets have delivered to the early earth? Sugahara and colleagues calculate that during the Late Heavy Bombardment, a period approximately 4 billion years ago when the Earth was subject to frequent strikes by asteroids and comets, concentrations of comet-derived oligopeptides could have been as high as 100 picomoles per liter: higher than concentrations thought to be possible from oligopeptide formation at hydrothermal vents, and comperable to what lightning in the atmosphere might have produced.
On the basis of this work, Sugahara was awarded the prestigious 2015 Geochemical Journal Award from the Geochemistry Society of Japan.