Chemical Discovery on Mars Suggests Origins of Life on Earth

Just over ten years ago, a robotic rover on Mars provided a long-awaited answer to a critical question: it confirmed the presence of organic material buried in the sediment of the planet’s ancient lakebeds.

Since then, we have continued to discover organic molecules on Mars, distributed in a manner indicating widespread carbon chemistry on our neighboring red planet.

However, this does not imply evidence of alien life; numerous non-biological processes can generate organic molecules. Yet, determining the exact source of these materials has remained a puzzle.

Evidence of Atmospheric Origins for Martian Molecules

Recently, a team led by planetary scientist Yuichiro Ueno from the Tokyo Institute of Technology has identified evidence suggesting that these molecules originate in the atmosphere. Here, carbon dioxide exposed to ultraviolet sunlight undergoes reactions, forming a mist of carbon molecules that subsequently precipitate onto the Martian surface.

While not as sensational as discovering Martian biology, this finding could provide insights into how the building blocks of life may have arrived on Earth billions of years ago.

“Such complex carbon-based molecules are essential prerequisites for life, the fundamental building blocks,” explains chemist Matthew Johnson from the University of Copenhagen.

“It’s akin to the age-old question of which came first, the chicken or the egg. We demonstrate that the organic material found on Mars arises from atmospheric photochemical reactions—without the presence of life. This is the ‘egg,’ the precondition for life. It remains to be determined whether this organic material led to life on the red planet.”

However, the concept that photolysis—where molecules break down under the influence of light—plays a role in Martian surface organic chemistry has been under discussion for some time. Johnson and colleagues proposed this hypothesis in a 2013 paper based on simulations, which subsequent studies have continued to explore.

Now, researchers need concrete evidence from Mars that corresponds with these simulation results.

Understanding Photolysis and Carbon Isotopes

Photolysis of CO2 results in the production of carbon monoxide and oxygen atoms. However, there are two stable isotopes of carbon. The most abundant is carbon-12, which has six protons and six neutrons. The slightly heavier isotope is carbon-13, containing six protons and seven neutrons.

Photolysis occurs more rapidly with the lighter isotope. Therefore, when UV light decomposes the mixture of carbon dioxide in the atmosphere containing both C-12 and C-13 isotopes, it preferentially depletes molecules with C-12, leaving behind a noticeable excess of C-13 carbon dioxide.

This enrichment of atmospheric carbon-13 was observed several years ago. Researchers analyzed a meteorite originating from Mars that landed in Antarctica. It contained carbonate minerals formed from CO2 in the Martian atmosphere.

“The conclusive evidence here is that the carbon isotope ratio matches precisely with our predictions from quantum chemical simulations,” Johnson explains.

“We lacked the other product of this chemical process to validate the theory, and now we have obtained it.”

Curiosity Rover Unveils Martian Carbon-13 Puzzle Piece

Moreover, the missing piece of this puzzle was uncovered in data collected by the Curiosity rover in Gale crater. Analysis of carbonate minerals found on the Martian surface revealed a depletion of carbon-13 that precisely mirrors the enrichment observed in the Martian meteorite.

“There is no other plausible explanation for both the carbon-13 depletion in the organic material and the enrichment in the Martian meteorite, relative to the consistent composition of volcanic CO2 emitted on Mars, which serves as a baseline similar to Earth’s volcanoes,” Johnson explains.

This compelling evidence suggests that the organic material discovered by Curiosity formed from carbon monoxide produced via photolysis.

This finding provides insights into the origins of organic material on Earth. Billions of years ago, when the Solar System was young, Earth, Venus, and Mars had very similar atmospheres, indicating that a similar process likely occurred on our planet.

Although Mars and Venus have since evolved differently and are currently inhospitable to known life forms in their unique ways, Mars’ rusty desert environment has provided valuable clues about our own origins.

“We haven’t yet discovered this definitive evidence here on Earth to substantiate that this process occurred, perhaps because Earth’s surface is significantly more dynamic, both geologically and biologically, undergoing constant change,” Johnson remarks.

“However, it’s a significant leap forward that we have now identified it on Mars, from a period when the two planets were remarkably similar.”

Read the original article on: Science Alert

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