Superflare Sparks of Life: How a stormy young sun might have launched life on Earth

A new study suggests that the earliest building blocks of life on Earth, viz[{” attribute=””>amino acids and carboxylic acids, may have been formed due to solar eruptions. The research suggests that energetic particles from the sun during its early stages, colliding with Earth’s primitive atmosphere, could have efficiently catalyzed essential chemical reactions, thus challenging the traditional “warm little pond” theory.

The first building blocks of life on Earth may have formed thanks to eruptions from our Sun, a new study finds.

A series of chemical experiments show how solar particles, colliding with gases in Earth’s early atmosphere, can form amino acids and carboxylic acids, the basic building blocks of proteins and organic life. The findings were published in the journal Life.

To understand the origins of life, many scientists try to explain how amino acids, the raw materials from which proteins and all cellular life, were formed. The best-known proposal originated in the late 1800s as scientists speculated that life might have begun in a “warm little pond”: A soup of chemicals, energized by lightning, heat, and other energy sources, that could mix together in concentrated amounts to form organic molecules.

In 1953, Stanley Miller of the University of Chicago tried to recreate these primordial conditions in the lab. Miller filled a closed chamber with methane, ammonia, water, and molecular hydrogen – gases thought to be prevalent in Earth’s early atmosphere – and repeatedly ignited an electrical spark to simulate lightning. A week later, Miller and his graduate advisor Harold Urey analyzed the chamber’s contents and found that 20 different amino acids had formed.

“That was a big revelation,” said Vladimir Airapetian, a stellar astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and coauthor of the new paper. “From the basic components of early Earth’s atmosphere, you can synthesize these complex organic molecules.”

But the last 70 years have complicated this interpretation. Scientists now believe ammonia (NH3) and methane (CH4) were far less abundant; instead, Earth’s air was filled with carbon dioxide (CO2) and molecular nitrogen (N2), which require more energy to break down. These gases can still yield amino acids, but in greatly reduced quantities.

Seeking alternative energy sources, some scientists pointed to shockwaves from incoming meteors. Others cited solar ultraviolet radiation. Airapetian, using data from NASA’s Kepler mission, pointed to a new idea: energetic particles from our Sun.

Kepler observed far-off stars at different stages in their lifecycle, but its data provides hints about our Sun’s past. In 2016, Airapetian published a study suggesting that during Earth’s first 100 million years, the Sun was about 30% dimmer. But solar “superflares” – powerful eruptions we only see once every 100 years or so today – would have erupted once every 3-10 days. These superflares launch near-light speed particles that would regularly collide with our atmosphere, kickstarting chemical reactions.

The energy of our young Sun – 4 billion years ago – helped create molecules in Earth’s atmosphere that allowed it to heat up enough to incubate life. Photo credit: NASA Goddard Space Flight Center/Genna Duberstein

“As soon as I published this paper, the team at Yokohama National University in Japan contacted me,” Airapetian said.

dr Kobayashi, a chemistry professor there, had spent the last 30 years studying prebiotic chemistry. He was trying to understand how galactic cosmic rays — incident particles from outside our solar system — might have affected Earth’s early atmosphere. “Most investigators ignore galactic cosmic rays because they need special equipment like particle accelerators,” Kobayashi said. “I was fortunate to have access to several of them near our facilities.” Minor changes to Kobayashi’s experimental setup could test Airapetian’s ideas.

Airapetian, Kobayashi, and their collaborators created a gas mixture that corresponded to the early Earth’s atmosphere as we understand it today. They combined carbon dioxide, molecular nitrogen, water and a variable amount of methane. (The proportion of methane in Earth’s early atmosphere is uncertain, but believed to be small.) They bombarded the gas mixtures with protons (simulating solar particles) or ignited them with spark discharges (simulating lightning), replicating the Miller-Urey experiment for comparison .

As long as the methane content was above 0.5%, the mixtures bombarded by protons (solar particles) produced detectable amounts of amino acids and carboxylic acids. But the sparks (lightning) required a methane concentration of about 15% before any amino acids formed.

“And even at 15% methane, the production rate of amino acids from lightning is a million times lower than from protons,” Airapetian added. Protons also tended to produce more carboxylic acids (a precursor to amino acids) than those ignited by spark discharges.

All else being equal, solar particles appear to be a more efficient source of energy than lightning. But everything else probably wasn’t the same, suggested Airapetian. Miller and Urey hypothesized that lightning was as common in the “warm little pond” period as it is today. But lightning coming from storm clouds formed by rising warm air would have been rarer under a 30% weaker sun.

“Cold conditions never have lightning, and early Earth was under a fairly weak sun,” Airapetian said. “That’s not to say it couldn’t be from lightning, but lightning seems less likely now and solar particles seem more likely.”

These experiments suggest that our active young Sun may have catalyzed the progenitors of life more easily, and perhaps earlier, than previously thought.

Reference: “Formation of Amino Acids and Carboxylic Acids in Weakly Reducing Planetary Atmospheres by Young Sun Solar Energetic Particles” by Kensei Kobayashi Jun-ichi Ise, Ryohei Aoki, Miei Kinoshita, Koki Naito, Takumi Udo, Bhagawati Kunwar, Jun-ichi Takahashi, Hiromi Shibata , Hajime Mita, Hitoshi Fukuda, Yoshiyuki Oguri, Kimitaka Kawamura, Yoko Kebukawa, and Vladimir S. Airapetian, April 28, 2023, Life.
DOI: 10.3390/life13051103