About 65 years ago, the US chemist Stanley Miller was experimenting with how the first building blocks of life could be formed. He suspected that lightning could have caused the gases of the primeval atmosphere to become the first organic compounds. The high-energy electrical discharges should also ensure that the chemically inert molecular nitrogen (N2) breaks down so that this building block of life can be better integrated into organic molecules. To this end, NASA researchers led by Vladimir Airapetian of the Goddard Space Flight Center have proposed an alternative strategy: they do not see weather events like lightning as a source of needed energy, but a cosmic event in the form of particularly strong solar storms.
Superflares from the young sun
The impetus for their theory was the observation of strong beam bursts on sun-like young stars by the Kepler Space Telescope. In contrast to our quiet sun today, these young stars throw more often so-called super flares out into space - outbreaks of radiation, which occur as a concomitant of coronal mass ejections. "The energy of these events is two to three times higher than that of the famous Carrington event, " explain Airapetian and his colleagues. In this strong solar storm in 1859, aurora appeared even over Hawaii and the Caribbean. From their observations, the researchers conclude that our sun, about four billion years ago, could have caused such strong solar storms much more frequently. "Our young sun then produced a ten times stronger magnetic flux than today, " the researchers report. "The frequency of the Super Carrington events it generated could therefore have been around 250 per day." Of these solar superflares, at least one daily hit probably also on the young earth.
And this is exactly what Airapetian and his colleagues believe is the key to the chemical processes that brought the first life to the stage: As they found out from a simulation, a strong burst of sunlight can bring enough energy into the Earth's atmosphere to generate chemical reactions to trigger and split the chemically inert molecular nitrogen. If the electromagnetically charged plasma cloud impinges on the earth's magnetic field, there will be a large amount of deformation and gaps in this protective grid, which normally prevents most of the charged cosmic particles from entering the atmosphere. "This creates an opening in the terrestrial magnetic field over the polar caps, " the scientists report.
As the simulation with the help of a chemical atmospheric model showed, these gaps in the primordial magnetic field of the earth could have made the decisive chemical reactions possible. Under the influence of the cosmic particles, the molecular nitrogen reacted to more usable and reactive compounds such as nitrogen oxide (N2O) and hydrogen cyanide (HCN). Although the latter is toxic, it is considered one of the essential building blocks for early life, because this compound forms the basis for nitrogen-containing biomolecules such as the amino acids. "The organic molecules created in the atmosphere could then have rained to the surface and formed there by chemical reactions more complex molecules, " said the NASA researchers. According to them, it was only the activity of our young sun that set the stage for the creation of the first life on our planet. display
Chemical heating for the young earth?
And something else could have caused the primeval superflares of the sun: they heat up the young earth strong enough to make the temperatures life-friendly and mild. For despite their high activity, our star emitted about four billion years ago significantly less energy than today. According to astronomers, the sun was 30 percent weaker at that time. In theory, it would have been much colder on the young earth than it is today - possibly too cold to keep water liquid. But that was clearly not the case. But why? It is known that the gases of the uranium atmosphere did not develop enough greenhouse effect to compensate for this lack of solar energy. But here the superflare scenario offers a solution: the nitrogen oxide (N2O) produced by these events in the earth's atmosphere is a greenhouse gas - and could therefore have served as a blanket for the young earth.
In an accompanying commentary, astrophysicist Ramses Ramirez of Cornell University considers it possible that the young Mars could have profited in similar ways from the sun's superflares. "Geological data suggest that Mars was also paradoxically warm around this time, " said the researcher. Since the Martian atmosphere also contained molecular nitrogen, the flares could have promoted "chemical heating" on our neighboring planet. "These results may also have implications for the climate and potential biology of Earth-like exoplanets around young sun-like stars, " Ramirez said.
- Vladimir Airapetian (NASA, Goddard Space Flight Center, Greenbelt) et al., Nature Geoscience, doi: 10.1038 / ngeo2719