How life arose on Earth remains one of science's most complex mysteries. One of the many myths and hypotheses is the possibility of meteorites delivering amino acids, known as life's building blocks, to our planet.
In a first-of-its-kind experiment, researchers have shown that amino acids might have formed in early meteorites from reactions driven by gamma rays produced inside space rocks due to the decay of radioactive elements.
According to a study published in ACS Central Science, scientists led by Yoko Kebukawa, an astrobiologist at Yokohama National University, had previously demonstrated that reactions between simple molecules, such as ammonia and formaldehyde, can synthesize amino acids and other macromolecules when exposed to gamma rays, provided liquid water and heat are required.
Radioactive elements produce gamma rays when they decay
When radioactive elements such as aluminum-26 — known to have existed in early carbonaceous chondrites — decay, they release gamma rays. The process provides the heat required to make biomolecules. Kebukawa wanted to detect the presence of radiation in forming amino acids in early meteorites, as per a release.
In an interview with Vice Motherboard, Kebukawa said, "As far as we know, it is the first time amino acids [have been produced] from formaldehyde and ammonia by gamma rays. We kind of expected that some amino acids would be produced, but the results were much better than expected, with quality and quantity. Various amino acids were produced by gamma-ray, and their amount was significant," she said.
The researchers dissolved formaldehyde and ammonia in water
In their experiment, the researchers dissolved formaldehyde and ammonia in water and sealed the solution in glass tubes. The latter was then irradiated with high-energy gamma rays produced from the decay of Cobalt-60.
The scientists found that the production of ?-amino acids, such as alanine, glycine, ?-aminobutyric acid, and glutamic acid, and ?-amino acids, such as ?-alanine and ?-aminoisobutyric acid, rose in the irradiated solutions as the total gamma-ray dose increased.
The researchers compared the results and the level of gamma-ray exposure that the decay of aluminum-26 could cause and estimated that it would have taken between 1,000 and 100,000 years to produce the amount of alanine and ?-alanine found in the Murchison meteorite, which landed in Australia in 1969.
The study opens a window into the reactions that warmed space rocks
"Amino acids can be produced non-biologically in various space environments," Kebukawa told Motherboard. "Among them, meteorite parent body processes are the final stage of organic evolution in space before being delivered to the Earth. The amino acids produced in meteorite parent bodies would be directly delivered to the ancient Earth as meteorites, and might become building blocks of life."
According to the researchers, their study proved that gamma ray-catalyzed reactions could produce amino acids, which contributed to the origin of life on Earth.
Study Abstract:
Carbonaceous chondrites contain life’s essential building blocks, including amino acids, and their delivery of organic compounds would have played a key role in life’s emergence on Earth. Aqueous alteration of carbonaceous chondrites is a widespread process induced by the heat produced by radioactive decay of nuclides like 26Al. Simple ubiquitous molecules like formaldehyde and ammonia could produce various organic compounds, including amino acids and complex organic macromolecules. However, the effects of radiation on such organic chemistry are unknown. Hence, the effects of gamma rays from radioactive decays on the formation of amino acids in meteorite parent bodies are demonstrated here. We discovered that gamma-ray irradiation of aqueous formaldehyde and ammonia solutions afforded a variety of amino acids. The amino acid yields had a linear relationship with the total gamma-ray dose but were unaffected by the irradiation dose rates. Given the gamma-ray production rates in the meteorite parent bodies, we estimated that the production rates were reasonable compared to amino acid abundances in carbonaceous chondrites. Our findings indicate that gamma rays may contribute to amino acid formation in parent bodies during aqueous alteration. In this paper, we propose a new prebiotic amino acid formation pathway that contributes to life’s origin.
