Solar eruptions may have been a catalyst for life on Earth, suggests new study

Early research, from the 1800s to the late 20th century, focused on lightning as the source of the formation of complex chemicals that resulted in prebiotic molecules. But this research says that energetic particles from the Sun are a more efficient energy source than lightning.

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

Airapetian co-authored another study in 2016 which suggested that during the Hadean stage, which is the Earth’s early formation period, the Sun was about 30% dimmer. But the intensity of the Sun's superflares was much greater. Superflares are powerful eruptions that today we only see once every 100 years, but when the Earth was first formed, they would have erupted once every 3-10 days. The 2016 study suggested that the Sun’s superflares would have regularly collided with the Earth’s atmosphere, kickstarting chemical reactions.

Airapetian and a team of international scientists created a mixture of gasses, namely carbon dioxide, molecular nitrogen, water, and a variable amount of methane, matching early Earth’s atmosphere. In order to answer the question of ‘Was it lightning or solar eruptions?’ they created two simulations. They first shot the gas mixtures with protons, which simulated solar particles. In the other simulation, they shot the gas mixtures with spark discharges, which simulated lightning.

They found that the gas mixtures shot by protons, containing 0.5% methane, produced a greater amount of amino acids in comparison to the spark discharges, which required at least 15% methane concentration before any amount of amino acids could be found. 

The study concluded that a younger Sun could have played a significant role in kickstarting the precursors of life.

Study abstract:

Life most likely started during the Hadean Eon; however, the environmental conditions which contributed to the complexity of its chemistry are poorly known. A better understanding of various environmental conditions, including global (heliospheric) and local (atmospheric, surface, and oceanic), along with the internal dynamic conditions of the early Earth, are required to understand the onset of abiogenesis. Herein, we examine the contributions of galactic cosmic rays (GCRs) and solar energetic particles (SEPs) associated with superflares from the young Sun to the formation of amino acids and carboxylic acids in weakly reduced gas mixtures representing the early Earth’s atmosphere. We also compare the products with those introduced by lightning events and solar ultraviolet light (UV). In a series of laboratory experiments, we detected and characterized the formation of amino acids and carboxylic acids via proton irradiation of a mixture of carbon dioxide, methane, nitrogen, and water in various mixing ratios. These experiments show the detection of amino acids after acid hydrolysis when 0.5% (v/v) of initial methane was introduced to the gas mixture. In the set of experiments with spark discharges (simulation of lightning flashes) performed for the same gas mixture, we found that at least 15% methane was required to detect the formation of amino acids, and no amino acids were detected in experiments via UV irradiation, even when 50% methane was used. Carboxylic acids were formed in non-reducing gas mixtures (0% methane) by proton irradiation and spark discharges. Hence, we suggest that GCRs and SEP events from the young Sun represent the most effective energy sources for the prebiotic formation of biologically important organic compounds from weakly reducing atmospheres. Since the energy flux of space weather, which generated frequent SEPs from the young Sun in the first 600 million years after the birth of the solar system, was expected to be much greater than that of GCRs, we conclude that SEP-driven energetic protons are the most promising energy sources for the prebiotic production of bioorganic compounds in the atmosphere of the Hadean Earth.