How, exactly, living things emerged on Earth remains a mystery. Now a new experiment has revealed that blasts of solar particles could have kickstarted the process by creating some of the basic components of life.
Time in the sun
Before so much as the first microbe existed, there had to be amino acids thought to have formed in one of the primordial oozes of early Earth. It was previously thought that lightning might have supercharged the formation of amino acids. However, Kensei Kobayashi of Yokohama National University in Japan, along with astrophysicist Vladimir Airapetian of NASA’s Goddard Space Flight Center and a team of researchers from both institutions, have found another possibility: The young Sun’s superflares probably helped give rise to the stuff of life.
“[Galactic cosmic rays] and [solar energetic particle] events from the young Sun represent the most effective energy sources for the prebiotic formation of biologically important organic compounds,” the researchers said in a study recently published in Life.
There is no definite answer for when life began, though scientists think the first organism on Earth made its debut sometime during the Hadean Eon (between 4 and 4.6 billion years ago). It was in 1953 that Stanley Miller and Harold Urey of the University of Chicago ran experiments that suggested that lightning striking Earth during that era provided conditions for chemical reactions that would result in amino acids. At the time, early Earth’s atmosphere was thought to be mostly water, hydrogen, ammonia, and methane. Miller and Urey simulated lightning striking these gas molecules in a lab and produced amino acids.
Problems with the lightning hypothesis began to arise when later studies indicated that there was not as much methane or ammonia in the Hadean atmosphere as Miller and Urey had assumed. Instead, there was much more carbon dioxide and molecular nitrogen. These gases must be broken down for the chemical reactions that form amino acids to occur, and lightning cannot break them down that easily. That would mean much smaller quantities of amino acids.
By studying observations of young, distant stars from NASA’s Kepler mission, the researchers figured out how the nascent Sun most likely behaved: It threw massive tantrums. These blasted Earth with enough energy to break down the atmospheric gases that existed at the time.
The Hadean Sun was young and temperamental. It would erupt in superflares—even an X-class solar flare has nothing on these phenomena. Superflares now only occur every hundred years or so, but back then, they likely happened at least once a week. Though an earlier study by Airapetian suggests our star was 30 percent dimmer during the Hadean Eon, the frequent superflares were still powerful enough to spark chemical reactions.
Kobayashi was then looking into the effects galactic cosmic radiation, or radiation from outside the Solar System, could have had on Earth’s atmosphere billions of years ago.
Kobayashi reached out to Airapetian after reading the study. Together, they used the particle accelerators at Yokohama University to investigate how protons from solar superflares could have interacted with Earth’s atmosphere. Their team simulated both solar radiation and lightning bombarding gas particles in a mixture that reflected the early Earth’s atmosphere. These results were also compared with Kobayashi’s previous work, which used particle accelerators to study the reactions triggered by galactic cosmic radiation.
The researchers found that the protons they shot at these gases, which were as close as possible to the gobs of plasma that would have exploded out of the young Sun during a superflare, were more effective at creating amino acids and one of their components, carboxylic acids, than either lightning or galactic cosmic rays.
“We have, for the first time, experimentally shown that the production rates of amino acids and carboxylic acids… due to proton irradiation can significantly exceed the production rates of these molecules via [galactic cosmic rays] and [lightning],” the researchers said.
Hadean Earth was also colder because the Sun was fainter, meaning the flashes of lightning Miller and Urey thought to be catalyzing amino acids were rarer than they are today. The researchers also think that highly energetic particles from the Sun may have had some part in generating amino acids on Mars. Before it lost most of its atmosphere, ancient Mars was warmer, wetter, and had a thicker atmosphere. It’s possible that it had been at least a temporary haven for life.
What turned chemicals into living organisms still eludes us. The Sun might not have zapped life into Earth, but life somehow became what it is from the biomolecules that it helped create.
Life, 2023. DOI: 10.3390/life13051103
Elizabeth Rayne is a creature who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. When not writing, she is either shapeshifting, drawing, or cosplaying as a character nobody ever heard of. Follow her on Twitter @quothravenrayne.