Young sun’s super solar flares helped set early Earth up for life

Solar outbursts may have supplied early Earth with the right stuff for life.

Based on telescope observations of young sunlike stars, researchers estimate that “super” solar flares bombarded Earth with energetic particles at least once a day around 4 billion years ago. Collisions between the particles and molecules in Earth’s atmosphere produced nitrous oxide, a planet-warming greenhouse gas, and hydrogen cyanide, a crucial component for building DNA, the researchers propose May 23 in Nature Geoscience.

Those chemical products warmed and fostered emerging life, says study coauthor Vladimir Airapetian, an astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Md. “Our sun, worshipped by ancient civilizations, wasn’t just a source of warmth, it also produced ingredients for life,” he says.
Life’s earliest traces date back to around 4.1 billion years ago (SN Online: 10/19/15). At the time, the sun was about 25 to 30 percent dimmer than it is today — too faint to keep Earth’s temperatures above freezing without the help of additional greenhouse gases (SN: 5/4/13, p. 30). Simulating the early sun using star data collected by NASA’s Kepler space telescope as a guide, Airapetian and colleagues found that while dim, the sun was probably wilder in its youth. Solar flares, also called coronal mass ejections, probably erupted more often and with more ferocity, producing storms 1,000 times as powerful as the most intense flares on record.

Those storms made a big impact on Earth, the researchers propose. The storms temporarily squeezed the magnetosphere, the protective magnetic bubble surrounding Earth, to one-sixth its normal height. That squashing allowed more solar particles to rain into the atmosphere. The dive-bombing particles ionized and broke apart nitrogen molecules in the air. Those molecules reassembled into new ones such as hydrogen cyanide, which can produce DNA bases and amino acids.

Another product, nitrous oxide, is a greenhouse gas nearly 300 times as potent as carbon dioxide. The additional nitrous oxide could have kept Earth from freezing during the sun’s dim days, the researchers propose.

The solar flares would have impacted more than just Earth. Similar effects would also have occurred on Mars, Airapetian adds, potentially improving the Red Planet’s habitability.

The interactions create the right molecules but in the wrong place, says Ramses Ramirez, an astrobiologist at Cornell University, who wrote an accompanying perspective piece in the same issue of Nature Geoscience. The flare-formed molecules would have originated in the upper atmosphere, not near the surface where most greenhouse warming takes place and where life would have taken root. While the idea is plausible, some other mechanism is needed to “get the molecules down so the critters can utilize them,” he says.