The Hadean Aeon is when life most likely first emerged, but little is known about the environmental factors that influenced the complexity of the chemistry. To understand the beginnings of abiogenesis, one must understand several ecological factors, including local (atmospheric, surface, and oceanic) and global (heliospheric) dynamics of the early Earth.
A new study suggests that the first building blocks of life on Earth may have originated from outbursts from our sun. Chemical experiments show how solar particles can create amino acids and carboxylic acids, the fundamental components of proteins and organic life, when they collide with gases in Earth’s early atmosphere.
Stanley Miller of the University of Chicago tried to recreate these primitive conditions in the lab in 1953. Methane, ammonia, water and molecular hydrogen — gases believed to be common in Earth’s early atmosphere — were added to a closed chamber by Miller. then repeatedly ignited an electrical spark to mimic lightning.
Miller and his graduate advisor Harold Urey examined the contents of the chamber a week later and found that 20 different amino acids had been created. And that was a big revelation.
But the past 70 years have made this interpretation difficult. Looking for alternative energy sources, some scientists pointed to shock waves from incoming meteors, while others pointed to ultraviolet radiation from the sun.
Vladimir Airapetian, a stellar astrophysicist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, and co-author of the new paper, pointed to energetic particles from our sun. His idea comes after observing data from NASA’s Kepler mission.
A study by Airapetian, published in 2016, claimed that the sun was 30% fainter during the first 100 million years of Earth’s existence. However, huge outbursts known as solar “superflares” – which we now see only once every 100 years or so – would have occurred every 3-10 days. These superflares launch particles that travel at nearly the speed of light, regularly hitting our atmosphere and triggering chemical reactions.
After publishing the paper, the team from Japan’s Yokohama National University contacted Airapetian.
Airapetian said: “Dr. Kobayashi, a chemistry professor there, had studied prebiotic chemistry for the past 30 years. He tried to understand how galactic cosmic rays – incoming particles from outside our solar system – may have affected Earth’s early atmosphere. “Most researchers ignore galactic cosmic rays because they need specialized equipment, such as particle accelerators.”
“I was lucky enough to have access to some of them near our facilities. Small adjustments to Kobayashi’s experimental set-up can test Airapetian’s ideas.”
Airapetian, Kobayashi and their collaborators created a mixture of gases that corresponds to the early Earth’s atmosphere as we understand it today. They combined carbon dioxide, molecular nitrogen, water and a variable amount of methane. They shot the gas mixtures with protons or ignited them with spark discharges (simulation of lightning), replicating the Miller-Urey experiment for comparison.
The mixtures launched by protons (solar particles) produced measurable levels of amino acids and carboxylic acids as long as the methane fraction was above 0.5%. But before amino acids could evolve, lightning’s arcing discharges required a methane concentration of about 15%.
Airapetian added, “And even at 15% methane, the amino acid production rate from lightning is a million times lower than from protons. Protons also tended to produce more carboxylic acids (a precursor to amino acids) than those ignited by arcing.”
“All else being equal, solar particles appear to be a more efficient source of energy than lightning. But everything else probably wasn’t equal.
Miller and Urey assumed that lightning was as common in the days of the “warm little pond” as it is today. But lightning, from storm clouds formed by rising warm air, would have been rarer under a 30% dimmer sun.
Airapetian said: “During cold conditions you never have lightning and the early Earth was under a faint sun. That’s not to say it couldn’t have been caused by lightning, but lightning now seems less likely and solar particles seem more likely.”
Magazine reference:
- Kensei Kobayashi et al. Formation of amino acids and carboxylic acids in weakly decaying planetary atmospheres by solar energetic particles from the young sun. To live. DOI: 10.3390/life13051103
