Powerful solar flares are likely the origin of life on Earth

The origin of life on Earth is one of the fundamental mysteries of modern science. Geophysical and fossil data indicate that they likely appeared more than four billion years ago, during the Stone Age. However, the environmental conditions that have contributed to the complexity of their chemistry are not well understood. In the late 19th century, it was speculated that the first organic molecules were created in a “primordial soup” of various chemicals. Lightning, heat, and other energy sources fueled this soup. In the 1950s, to test this hypothesis, University of Chicago biologist Stanley Miller and chemist Harold Heary set out to simulate conditions on early Earth in a laboratory—in Miller’s famous experiment. – Uri.

The search for a sufficient source of energy at the origin of life

It was assumed at the time that the Earth’s early atmosphere was shrinking severely. Then there would be an abundance of methane (CH4), ammonia (NH3) and water (H2O). So the two scientists reproduced these conditions in a closed room. Then they used an electric spark as the energy source (to simulate lightning). After a few days, they had already discovered that about twenty different amino acids had formed. A good start in life…

However, subsequent photochemical studies indicated that ammonia and methane were in fact in low amounts. Ultraviolet emissions from the young sun would have quickly destroyed them. Geochemical data indicated that Earth’s atmosphere was instead dominated by a mixture of nitrogen (N2) and carbon dioxide (CO2). It resulted from the release of global volcanic gases on the planet. However, the Miller-Urey experiment conducted with these conditions did not produce prebiotic particles.

Also read: How scientists are searching for the origin of life on Earth

N2 and CO2 can still produce amino acids, but in much smaller amounts. Photodissociation of N≡N bonds requires more energy. In addition, the element nitrogen (N) is essential for the formation of amino acids. Therefore, scientists searched for alternative energy sources for lightning bolts. Some pointed to the shock waves produced by meteorites, while others cited solar ultraviolet radiation.

But galactic cosmic rays are quickly emerging as a more acceptable energy source. Proton irradiation experiments in gas mixtures containing CH4 (or CO), N2 and water resulted in sustained production of amino acids. This was much better than lightning or ultraviolet rays. But it turns out that the intensity of galactic cosmic radiation during the Pacific period was much lower than it is today. In contrast, the supersolar planets were particularly frequent and very energetic. There was energy up to 1,000 times greater than that observed today.

Solar radiation is 30% less than it is today

Vladimir Irapetyan is a stellar astrophysicist at NASA’s Goddard Space Flight Center. So he relied on data from NASA’s Kepler mission to propose a new hypothesis. The Sun’s energetic particles, released during these supernovae, may have been the origin of life, the first building blocks of life on Earth.

The Kepler telescope was launched in 2009 with the goal of making a census of exoplanets residing in a particular region of the Milky Way galaxy, which orbit sun-like stars. For nearly ten years, he has observed distant stars at different stages of their life cycles. The data collected has also provided insight into our sun’s past. Study published in 2016 It shows that about four billion years ago, the Earth received only about 70% of the Sun’s energy compared to today.

Read also: How did Earth become a habitable planet?

Giant flares rocked the surface of the Sun, spewing huge amounts of matter and radiation into space. Today, we only observe such eruptions about once every 100 years. ” During the first 100 million years corresponding to the beginning of the era (4.4 billion years ago), solar superplanets occurred at a rate of one event every 3 to 10 days So solar particles could collide with Earth’s atmosphere, triggering chemical reactions at the origin of life.

With the help of Professor Kensei Kobayashi of Yokohama National University, who has spent the past 30 years studying the chemistry of prebiotics, Airapetian set out to examine the composition of amino acids and carboxylic acids in Earth’s atmosphere. , CH4 and H2O in different proportions. They bombarded these gaseous mixtures with protons. The goal is to simulate solar particles. The researchers also used electrical discharges as another source of energy to simulate lightning, for comparison. The results of their experiments have been published in review life.

More effective signs of life

The researchers and their team report that as long as the percentage of methane is greater than 0.5%, the bombardment of protons yields detectable amounts of amino acids and carboxylic acids. In contrast, a methane concentration of about 15% is required for the formation of amino acids via discharge sparks. ” Even at 15% methane, the rate at which amino acids are produced by lightning is a million times lower than the rate at which protons are produced. », Airapetian added.

Carboxylic acid yields formed from gaseous mixtures of CO2, CH4, N2 and H2O by spark discharge (SD) or proton irradiation (PI). The methane content was 0%, 5% or 25% as shown in the figure. C1: formic acid. C2: acetic acid. C3: propanoic acid. iC4: isobutyric acid. iC5: isovaleric acid. C2di: oxalic acid. C3di: malonic acid. C4di: succinic acid. C5di: glutaric acid. Credits: Kobayashi et al., Life (2023)

Furthermore, experiments have shown that protons tend to produce more carboxylic acids (precursors of amino acids) from the spark discharge. In conclusion, all other things being equal, solar particles seem to be a more efficient source of energy than lightning. ” Things may not have been equal though. Airapetian noted.

Also read: Many forms of microbial life existed in the early Earth

Miller and Urey hypothesized that lightning was as prevalent four billion years ago as it is today. However, Airapetian believes that lightning was very rare when the sun was 30% weaker. ” In cold conditions, there is no lightning at all, and the early Earth was under fairly weak sunlight. This does not mean that lightning cannot be the cause of this phenomenon. However, it seems less likely today, and solar particles seem more likely he explains.

The results also indicate that the endogenous production of amino acids on Earth via solar-active particles could exceed the extraterrestrial production through the effects of comets and carbonaceous chondrites. In short, these recent experiments suggest that our young Sun, which was particularly active at the time, could have provided the energy needed to form the primordial elements of life. All this easier and perhaps earlier than previously thought.