Scientists are uncertain about the origins of life on Earth, but one hypothesis is that meteorites brought amino acids, the building blocks of life, to the planet. Researchers have found that amino acids could have formed in early meteorites due to reactions within the space rocks caused by gamma rays.
Even as detailed images of distant galaxies from the James Webb Space Telescope show us more of the greater universe, scientists still disagree about how life began here on Earth. One hypothesis is that meteorites delivered amino acids<div class="cell text-container large-6 small-order-0 large-order-1">
<div class="text-wrapper"><br />Amino acids are a set of organic compounds used to build proteins. There are about 500 naturally occurring known amino acids, though only 20 appear in the genetic code. Proteins consist of one or more chains of amino acids called polypeptides. The sequence of the amino acid chain causes the polypeptide to fold into a shape that is biologically active. The amino acid sequences of proteins are encoded in the genes. Nine proteinogenic amino acids are called "essential" for humans because they cannot be produced from other compounds by the human body and so must be taken in as food.<br /></div>
</div>” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>amino acids — life’s building blocks — to our planet. Now, researchers reporting in the journal ACS Central Science have experimentally shown that amino acids could have formed in these early meteorites from reactions driven by gamma rays produced inside the space rocks.
Ever since Earth was a newly formed, sterile planet, meteorites have been hurtling through the atmosphere at high speeds toward its surface. If the initial space debris had included carbonaceous chondrites — a class of meteorite whose members contain significant amounts of water and small molecules, such as amino acids — then it could have contributed to the evolution of life on Earth. However, the source of amino acids in meteorites has been hard to pinpoint.
In previous lab experiments, Yoko Kebukawa and colleagues showed that reactions between simple molecules, such as ammonia and formaldehyde, can synthesize amino acids and other macromolecules, but liquid water and heat are required. Radioactive elements, such as aluminum-26 (26Al) — which is known to have existed in early carbonaceous chondrites — release gamma rays, a form of high-energy radiation, when they decay. This process could have provided the heat needed to make biomolecules. So, Kebukawa and a new team wanted to see whether radiation could have contributed to the formation of amino acids in early meteorites.
The researchers dissolved formaldehyde and ammonia in water, sealed the solution in glass tubes, and then irradiated the tubes with high-energy gamma rays produced from the decay of cobalt-60. They found that the production of α-amino acids, such as alanine, glycine, α-aminobutyric acidAny substance that when dissolved in water, gives a pH less than 7.0, or donates a hydrogen ion.” data-gt-translate-attributes=”[{“attribute”:”data-cmtooltip”, “format”:”html”}]”>acid and glutamic acid, and β-amino acids, such as β-alanine and β-aminoisobutyric acid, rose in the irradiated solutions as the total gamma-ray dose increased.
Based on these results and the expected gamma-ray dose from the decay of 26Al in meteorites, the researchers estimated that it would have taken between 1,000 and 100,000 years to produce the amount of alanine and β-alanine found in the Murchison meteorite, which landed in Australia in 1969. This study provides evidence that gamma ray-catalyzed reactions can produce amino acids, possibly contributing to the origin of life on Earth, the researchers say.
Reference: “Gamma-Ray-Induced Amino Acid Formation in Aqueous Small Bodies in the Early Solar System” by Yoko Kebukawa, Shinya Asano, Atsushi Tani, Isao Yoda and Kensei Kobayashi, 7 December 2022, ACS Central Science.
DOI: 10.1021/acscentsci.2c00588
The authors acknowledge funding from the Japan Society for the Promotion of Science KAKENHI.
Source: SciTechDaily
