Day 4

Determining how life arose used to involve simply asking where its constituent molecules came from. Some ferment of simpler chemicals bubbling in a tarry pool, sparked by lightning? Ready-made molecules like amino acids, the components of proteins, delivered on a crashing comet? This week Nature Geoscience reported another idea: that spectacularly large flares released by the young sun could have sent high-energy particles screaming through the mundane gases of Earth’s early atmosphere, splitting them into bits that could reassemble into complex organic molecules. The cometary-delivery idea got a boost as well: amino acids have been spotted on comets before, but a study in Science Advances this week revealed that 67P/Churyumov-Gerasimenko, a comet being stalked by the European space probe Rosetta, has them too. The universe, it seems, has no problem amassing life’s raw ingredients. The question now is: what were the processes that cooked them up into something interesting?