Turner reported in late 2022 that radioactive isotopes were found to produce amino acids inside carbonaceous chondrite meteorites. A special type of radioactive meteorite could have seeded life on Earth, a new study found. Carbonaceous chondrites, a type of radioactive meteorite with water and organic compounds, produce energetic gamma rays that can drive the chemical reactions to synthesize amino acids — the building blocks of life — researchers discovered.
Meteorites are leftovers from the formation of the young solar system’s rocky inner planets, which first clotted from the hot clouds of gas and dust billowing near the sun roughly 4.6 billion years ago. At the time, the planets were too close to the sun to form oceans and so couldn’t harbor life, leaving scientists puzzling over how Earth transformed into an oasis of life from its initial barren state. A previous study suggested that water could have been brought to Earth by carbonaceous chondrite meteorites. Now a new study, published Dec. 7 in the journal ACS Central Science, shows that the same meteorites might have brought life’s building blocks too.
To see if this was possible, the researchers mixed ammonia, methanol and formaldehyde into water in quantities similar to those found inside meteorites. Then, to see if the radioactive, gamma-ray producing elements such as aluminum-26 inside the meteorites could generate the heat needed for amino acid synthesis, the researchers irradiated their mixture with gamma rays from an analog isotope called cobalt-60.
Sure enough, the scientists found that the gamma-ray bombardment caused a spike in the production of amino acids inside the solution. Higher gamma-ray production increased the rate of amino acid synthesis. Additionally, the researchers discovered that the proportions of lab-produced amino acids matched those found in the Murchison meteorite — a 2205-pound (100 kilograms) space rock that landed in Australia in 1969. Further analysis revealed that it would have taken anywhere from 1,000 to 100,000 years to produce the amino acid quantities found inside the Murchison meteorite.
It should be noted that amino acids can be made by many different processes, so while the mechanism the researchers have discovered is a possible candidate for how Earth was seeded by amino acids, it is not the only one. Future research will need to compare this mechanism with others to establish which one likely predominated during Earth’s earliest years.
Lea also reported on this subject in late 2022 where Kebukawa, et al., indicated that if that early bombardment included a class of meteorites called carbonaceous chondrites — which contain significant amounts of water and small molecules, such as amino acids — this space-rock delivery system could have contributed significantly to the emergence of life on our planet. Yet how these molecules formed within meteorites in the first place has remained a puzzle — one that Yokohama National University astrobiologist and cosmochemist Yoko Kebukawa and her team think they may be on a path to solving, according to a statement.
In previous experiments, Kebukawa and colleagues had shown that reactions between simple molecules, such as ammonia and formaldehyde, can synthesize amino acids and other macromolecules. But for this to happen, liquid water and heat would be required. The team wanted to know if this heat could have been supplied when radioactive isotopes, like aluminum-26 — which is known to exist within carbonaceous chondrite meteorites — decayed and released high-energy radiation called gamma-rays.
To test this idea, Kebukawa and her team dissolved formaldehyde and ammonia in water and then sealed the resultant solution in glass tubes. These tubes were then irradiated with gamma-rays created by the decay of the radioactive isotope cobalt-60. The scientists discovered that this process caused the creation rate of alpha-amino acids, like alanine, glycine, alpha-aminobutyric acid and glutamic acid; as well as beta-amino acids, such as beta-alanine and beta-aminoisobutyric acid, to increase. Additionally, the team found that increasing the total dose of gamma-rays that the samples were exposed to boosted the production rate of these biomolecules.
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