Scientists ask: Is the origin of life outside the Earth? 2022-04-28 09:02:24

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Meteorites deliver organic matter
This concept image shows meteorites transporting nuclear bases to ancient Earth. Nuclear bases are represented by structural diagrams with hydrogen atoms as white spheres, carbon in black, nitrogen in blue, and oxygen in red.

NASA Goddard/CI Lab/Dan Gallagher

The origins of life are unknown. Did it arise spontaneously from hydrothermal vents, or when lightning struck a pool of sludge? How were all the necessary components put in the right place at the right time? Is the emergence of life on Earth inevitable? Or did meteorites bring some necessary ingredients?

about 10 years agoScientists at NASA and elsewhere have used sophisticated techniques to look at meteorites and find conclusive evidence for many of the particles considered. prebiotic, including the purine nuclear bases, guanine and adenine that are part of DNA. While scientists haven’t found everything needed to encode genetic information, the discovery established active organic chemistry taking place on asteroids.

Now, Yasuhiro Oba (Hokkaido University, Japan) and his colleagues have analyzed three meteorites and found something new: In addition to the previously discovered purine nuclear bases, they have discovered the “missing” nucleopidin bases (cytosine, uracil, thymine) that make up the rest of the meteorites. DNA / RNA alphabet.

To do this, the team developed a new, milder extraction method. “Hot formic acid has long been considered best for extracting nucleobases from natural samples,” explains Oba. But this sometimes leads to the decomposition of organic molecules or their hydrolysis. Instead, we used ultrasound technology in cold water.”

Ultrasound Intense ultrasound is forced through liquids, creating shock waves that “screw” the particles into the medium. When Oba’s group used this technique on samples of meteorite finely crushed in water, it revealed a greater diversity of organic molecules.

Murchison meteorite fragment
This is a small part of the Murchison meteorite, which broke into 100 kg of fragments that fell in Australia in 1969. Decades of research have shown the presence of organic compounds in these parts of the carbonaceous chondrite meteorite.
Punampiroma et al. / Nature 1970

But how can scientists know that organic molecules, nuclear bases, etc., are in fact extraterrestrial? The OBA group can test this directly using one of the meteorites they took as a sample: the “Murchison” meteorite, discovered in 1969 in Murchison, Australia. The researchers compared the soil in the Murchison impact crater to the meteorite sample to confirm that the nuclear bases had arrived with the impactor and were not of terrestrial origin.

“Although some nuclear bases have been identified in the soil sample, the concentration and molecular distribution are clearly different from those detected in the Murchison meteorite,” says Oba.

The Murchison meteor is 7 billion years, so it formed when the Sun was still a protostar. The presence of the rock’s original prebiotic particles (not its impact landing) could support the theory that life on Earth has an extraterrestrial origin.

Michael Callahan (Boise State University), who performed the above-mentioned analyzes of nuclear bases in meteorites, says the new study “improved the limits of discovery and enabled the identification of pyrimidines.” But he cautions that pyrimidines are found in concentrations so low that the result precludes further speculative conclusions. “If these findings represent typical pyrimidine concentrations in meteorites, it is likely that geochemical synthesis on early Earth was responsible for the emergence of genetic material rather than input from extraterrestrial conduction,” he explains.

Then again, it is not clear whether these meteorites represent the general population of space rocks that reach Earth, now or in the distant past. Sample return missions from asteroids Ryugu and Bennu will help us understand the evolution of extraterrestrial organic molecules. The methods devised by the OBA group could prove invaluable in determining the true composition of these pure asteroids, as well as the origin of complex organic molecules in interstellar space.


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