Life On Earth May Have Had A Cold Start

After decades of speculation surrounding the origins of life on Earth, a team of astrobiologists remains perplexed by two significant challenges. The first dilemma involves the transformation of simple molecules into complex ones. The second challenge is attributable to the faintness of our early Sun and its impact on the existence of liquid water on Earth's surface, a phenomenon known as the Faint Young Sun Paradox.

Vladimir Airapetian, a senior astrophysicist at NASA Goddard Space Flight Center, shared these findings at the Origins 2026 conference in Paris. While liquid water at the surface remains a fundamental aspect of astrobiology, it is not the sole factor in determining a planet's habitability. Over 4 billion years ago, the Sun was considerably weaker, and Earth should have been frozen over if not for the presence of liquid water in the equatorial belt.

Airapetian posits that energy might have originated from the ejection of billions of tons of coronal mass ejections from young stars, resulting in highly energetic protons that could have broken apart atmospheric molecules like nitrogen (N2) and carbon dioxide (CO2). The other major conundrum lies in the Faint Young Sun, as the planet would require a significant amount of carbon dioxide to warm up, turning small ponds highly acidic.

However, this could hinder the formation of prebiotic chemistry and life, making it difficult to progress towards complexity. Airapetian and his colleagues used ten percent of nitrous oxide produced experimentally in the early Earth's atmosphere to demonstrate that an equatorial band could have been warmed to 2 to 3 degrees centigrade, suggesting a cold start to life.

This scenario would also prevent organic molecules like hydrogen cyanide from evaporating from small lakes while promoting further chemical complexity. Alkaline conditions, rather than acidic ones, are necessary for life; an example being the importance of alkaline boron for stabilizing ribose, a crucial molecule for ribonucleic acid (RNA) and DNA production.

Airapetian acknowledges that the exact origin and timeline of life on Earth may remain unknown. However, over the next two decades, astrobiologists like Airapetian will utilize new ground and space telescopes to search for biosignatures on rocky planets orbiting solar-type stars. Prebiotic chemistry on these planets is expected to be similar, but once it progresses, it will likely diverge into a unique pathway.

In the search for life beyond our solar system, Airapetian favors looking for the spectroscopic traces of nitrous oxide in the atmospheres of exoearth planets, as it would indicate the presence of atomic nitrogen capable of forming complex molecules.