A coronal mass ejection hits Earth's atmosphere like a cannonball. The cloud of solar matter, created during storms on the sun, will fizzle through the thinnest parts of Earth's protective magnetic field and send waves of light dancing across the polar night skies. It can disrupt communications and fry electrical grids. And if our planet's protection was just a bit weaker, and more of that explosive solar matter reached the surface, the consequences for life could be devastating.
But it also may have helped make life on Earth possible. That's according to a study published Monday in the journal Nature Geoscience, theorizing that extremely powerful and frequent coronal mass ejections from a stormy young sun could have warmed our infant planet, helping make conditions suitable for life about 4 billion years ago.
"It shows how even harmful things in moderation can be helpful, especially in the very early stage," said Dimitar Sasselov, an astronomer at Harvard University and the director of the school's Origins of Life Initiative. Sasselov was not involved in the study.
The new research seeks to explain what scientists call the "faint young sun paradox" — the fact that when the solar system was newly created, the Earth managed to stay warm enough for water to be liquid even though the sun was 30 percent fainter then than it is now.
It's generally thought that greenhouse gases helped keep the planet toasty, though figuring out which gases were present and how they got into the atmosphere has proved a challenge. Violent volcanic activity would have produced carbon dioxide, but not enough to make up for a 30 percent heat deficit. Methane and water vapor, which also trap heat, probably were not prevalent enough to do the job on their own.
Nitrous oxide, the "laughing gas" you get at the dentist, seems like a good candidate. It produces a greenhouse effect 300 times as powerful as carbon dioxide. Molecular nitrogen — a molecule made of two nitrogen atoms bound together — makes up 80 percent of the atmosphere today. But it's also incredibly hard to break apart; even now, fairly sophisticated biological processes are needed to do so. Before life, Earth had no mechanism for convincing the relatively inert gas to interact with other molecules, but life couldn't exist unless nitrogen teamed up with other elements. Thus the paradox.
All of this was on the mind of Vladimir Airapetian, lead author of the Nature Geoscience study and an astronomer at NASA, when he was assigned to a task force analyzing how coronal mass ejections (CMEs) could wreak havoc on Earth today. As he examined the effects of an intense solar storm on Earth's atmosphere, he found himself thinking about the infant suns he studied as a graduate student in Armenia decades ago.
Those new, small stars, he knew, tend to behave like "big babies."
"When [stars] are young, they explode much much more frequently," Airapetian said, much as newborns throw tantrums. Modeling this behavior, he found that those early, frequent storms would have been powerful enough to cut through the magnetic field and surge into the lower atmosphere. There, they would have provided the energy needed to blast apart molecular nitrogen and persuade it to interact with other gases, such as carbon dioxide and methane, producing nitrous oxide.
Real-world observations seem to bear out those calculations. Studies have shown that the level of nitrous oxide in the upper atmosphere surges in the wake of summer lightning storms. Airapetian thinks that frequent, powerful CMEs could have had an even more lasting effect.
And that's just the beginning. Airapetian's chemist colleagues pointed out that, in addition to producing nitrous oxide, these interactions would have created hydrogen cyanide. Like CMEs, this chemical is usually thought of as dangerous — even lethal. But in the right doses on early Earth (when there was nothing around for it to kill) hydrogen cyanide would have helped give rise to amino acids — the building blocks for proteins that life desperately needs.
"And now it becomes really, really interesting," Airapetian said. With the right temperatures and the right ingredients, "life can start the process of cooking."
Sasselov, the Harvard astronomer, said that this study complements what is already known about how greenhouse gases may have helped warm the Earth. Other studies have suggested that micrometeorites provided the spark that turned nitrogen into nitrous oxide, but "this might be a case where having two possibilities is better than one," he said. Neither mechanism would have produced very many nitrous oxide molecules, and early Earth needed as many greenhouse gases as it could get.
"The point about this kind of mechanism of producing additional greenhouse gas is ... you can add it to the other ones," he said. "The more the merrier."
Both agree that the study has implications for worlds far beyond our own. If intense solar storms can help explain how life got started on Earth, they may help us identify other planets where life could be in the process of "cooking."
"Our ultimate goal is to find something like that," Airapetian said. "When we find it, that's when I'll be happy. Now I'm half-happy."