Scientists have discovered that the most energetic beams of light in the universe, known as gamma rays, may have played a key role in the emergence of life on Earth, a finding that provides clues about one of the ultimate mysteries in science, reports a new study.
In a first-of-its-kind experiment, researchers showed that compounds called amino acids, which are the building blocks of life, can be forged by gamma rays that erupt inside space rocks due to the decay of radioactive elements. The results pinpoint one possible origin for the amino acids that ended up strewn across Earth billions of years ago, enriching our planet with the necessary ingredients for life.
The question of how life arose has inspired countless myths across time and cultures, and it has also become one of the most enduring problems in science. Scientists have long suspected that some of the ingredients for life were delivered to Earth by space rocks that pelted its surface more than four billion years ago. However, it’s not clear what kinds of amino acids might have existed within these ancient meteorites, or how they might have formed.
Now, scientists led by Yoko Kebukawa, an astrobiologist at Yokohama National University, have experimentally demonstrated that formaldehyde and ammonia, common compounds in space rocks, can transform into amino acids when exposed to gamma rays, a finding that points to “a new prebiotic amino acid formation pathway that contributes to life’s origin,” according to a study published in ACS Central Science.
“As far as we know, it is the first time amino acids [have been produced] from formaldehyde and ammonia by gamma-rays,” Kebukawa said in an email to Motherboard, adding that her team was “surprised by the results.”
“We kind of expected that some amino acids would be produced, but the results were much better than expected, with quality and quantity,” she continued. “Various amino acids were produced by gamma-ray and their amount was significant.”
Kebukawa and her colleagues had previously demonstrated that ammonia and formaldehyde could transform into amino acids, and organic molecules, in the presence of liquid water and heat. Ammonia, formaldehyde, and water are all present in carbonaceous chondrites, an ancient group of space rocks, leading scientists to believe that these meteorites played an important role in making Earth habitable. However, the heat source that catalyzed the reactions that make amino acids has remained unclear.
In the new study, Kebukawa’s team explored the possibility that gamma rays created by the decay of radioactive atoms, such as aluminum isotopes, may have been the cauldron that cooked up these primordial biomolecules. To do this, the researchers exposed tubes of dissolved ammonia and formaldehyde to gamma rays emitted by the decay of cobalt isotopes.
The experiment created a panoply of compounds that are useful to living creatures, including alanine, glycine, and several beta amino acids. What’s more, the team estimated that it would take fewer than 100,000 years for some amino acids to reach the abundances seen in a rock like the Murchison meteorite, a carbonaceous chondrite that landed in Australia in 1969. This short timeframe hints that amino acids were probably common in carbonaceous chondrites in the early solar system, bolstering the notion that these rocks helped to pave the way for life on Earth—and perhaps other planets.
“Amino acids can be produced non-biologically in various space environments,” Kebukawa explained. “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.”
“Similar to the Earth, such amino acids could be delivered to ancient Mars where the weather was mild and there were oceans,” she added. “Also, amino acids produced by gamma rays possibly occurred in the subsurface ocean worlds in icy moons such as Enceladus” within “a few million years after the solar system formation” before the radioactive gamma ray sources were depleted.
The researchers hope to build on these findings by exploring whether gamma rays might produce other kinds of organic compounds that were important to the emergence of life. While there are still far more questions than answers when it comes to life’s origins, the new study opens a tantalizing window into the energetic reactions that briefly warmed space rocks billions of years ago, potentially converting them into seeds that would ultimately blossom into the vibrant biosphere we inhabit today.