A stormy, active sun may have started life on Earth

2023-05-02 19:17:24

Artist’s concept of life on Earth – NASA

MADRID, 2 May. (EUROPA PRESS) –

A series of chemical experiments have shown how solar particles, when colliding with gases in the Earth’s early atmosphere, can form amino acids and carboxylic acids, the building blocks of protein and organic life.

The findings, which suggest that our young and active Sun could have catalyzed the precursors of life more easily, and perhaps sooner, than previously assumed, were published in Life magazine.

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, were formed. The best-known proposal originated in the late 19th century when scientists speculated that life might have started in a “little warm pond”: a soup of chemicals, energized by lightning, heat, and other energy sources, that could be mixed in concentrated amounts to form organic molecules.

In 1953, Stanley Miller of the University of Chicago tried to recreate these primordial conditions in the laboratory. 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 contents of the chamber and they discovered that 20 different amino acids had been formed.

“That was a great revelation,” he said. it’s a statement Vladimir Airapetian, a stellar astrophysicist at NASA’s Goddard Space Flight Center and a co-author of the new paper. “From the building blocks of the early Earth’s atmosphere, you can synthesize these complex organic molecules.”

But the last 70 years have complicated this interpretation. Scientists now believe that ammonia (NH3) and methane (CH4) were much 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 produce amino acids, but in greatly reduced amounts.

Looking for alternative power sources, some scientists pointed to shock waves from incoming meteorites. Others cited solar ultraviolet radiation. Airapetian, using data from NASA’s Kepler mission, points to a new idea: energetic particles from our Sun.

Kepler observed distant stars at different stages of their life cycles, but their data provide clues to our Sun’s past. In 2016, Airapetian published a study suggesting that for Earth’s first 100 million years, the Sun was a 30% darker. But solar “superflares,” powerful flares that we only see once every 100 years or so today, would have erupted once every 3-10 days. These superflares launch particles at close to the speed of light that would regularly collide with our atmosphere, starting chemical reactions.

“As soon as I published that article, the Japan National Yokohama University team contacted me,” Airapetian said.

Dr. Kobayashi, a chemistry professor there, he spent the last 30 years studying prebiotic chemistry. He was trying to understand how galactic cosmic rays (incoming particles from outside our solar system) might have affected the early Earth’s atmosphere. “Most researchers ignore galactic cosmic rays because they require specialized equipment, such as particle accelerators,” Kobayashi said. “I was lucky enough to have access to several of them near our facility.”

Airapetian, Kobayashi, and their collaborators created a mixture of gases that matched 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 is believed to be low.) They fired 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 proportion of methane was greater than 0.5%, the mixtures fired by protons (solar particles) produced detectable amounts of amino acids and carboxylic acids. But spark discharges (lightning) required about 15% methane concentration before amino acids were formed.

“And even with 15% methane, lightning’s amino acid production rate is a million times slower than protons,” Airapetian added. The protons also tended to produce more carboxylic acids (a precursor to amino acids) than those ignited by spark discharges.

Other things being equal, solar particles appear to be a more efficient source of energy than lightning. But all else was probably not equal, Airapetian suggested. Miller and Urey assumed that lightning was just as common in the days of the “warm little pond” as it is today. But lightning, which comes from storm clouds formed by rising warm air, they would have been rarer under a 30% darker Sun.

“During cold conditions, there is never any lightning, and the early Earth was under a fairly dim Sun,” Airapetian said. That’s not to say it couldn’t come from lightning, but it now seems less likely to be lightning, and solar particles seem more likely.”