Meteorites could have brought the 5 genetic “letters” of DNA to Earth


Conceptual image of meteorites delivering nucleobases to ancient Earth.

Photo: NASA Goddard/CI Lab/Dan Gallagher/Courtesy

All the key building blocks of DNA have now been discovered in meteoritessuggesting that cosmic impacts could have helped bring these ingredients to Earth and help in the beginning of life on the planet in formation.

Using new analyses, scientists have just found the last two of five informative units of DNA and RNA that had not yet been discovered in meteorite samples, NASA said in a statement.

While it is unlikely that DNA could be formed in a meteorite, this discovery demonstrates that these genetic parts are available for delivery in space rocks and could have contributed to the development of the instructive molecules of life on early Earth.

The discovery, made by an international team with NASA researchers, provides more evidence that chemical reactions in asteroids can produce some of the ingredients of lifeand that they could have been delivered to ancient Earth by meteorite impacts or perhaps by infalling cosmic dust.

All the DNA and RNA, which contains the instructions to build and operate for every living thing on Earth, contains five informative components, called nucleobases.

Until now, scientists looking for them in extraterrestrial samples had only found three of the five. However, a recent analysis by a team of scientists led by Associate Professor Yasuhiro Oba of Hokkaido University, Hokkaido, Japan, he identified the final two nucleobases that had eluded scientists.

What does the team that discovered them say?

Nucleobases belong to classes of organic molecules called purines and pyrimidines, which have a wide variety. Nevertheless, it remains a mystery why more types have not been discovered in meteorites so far.

“I wonder why purines and pyrimidines are exceptional in that they do not show structural diversity in carbonaceous meteorites unlike other classes of organic compounds such as amino acids and hydrocarbons?” said Oba, lead author of a paper on the research published April 26 in Nature Communications. “Since purines and pyrimidines can be synthesized in extraterrestrial environments, as our own study has shown, one would expect to find a wide diversity of these organic molecules in meteorites.”

“We now have evidence that the full set of nucleobases used in current life could have been available on Earth when life arose,” said Danny Glavin, co-author of the articlefrom NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

how they did it

The researchers used state-of-the-art analytical techniques originally designed for use in genetic and pharmaceutical research.

This newly discovered nitrogenous base pair, cytosine and thymine, it has been elusive in previous analyzes due to its more delicate structure, which may have been degraded in samples previously.

But Two factors may have contributed to the new discovery: First, the team used cold water to extract the compounds rather than hot formic acid, which is highly reactive and could have destroyed these brittle molecules in earlier samples. Second, more sensitive assays were used that could detect smaller amounts of these molecules.

“This group has achieved a technique that is more like cold infusion than hot tea and is capable of extracting more delicate compounds,” said Jason Dworkin, co-author of the paper at NASA Goddard. “I was surprised that they had seen cytosine, which is very fragile.”

It is not a proof that we are aliens

the find does not provide definitive proof as to whether life on Earth was helped from space or produced exclusively in the prebiotic soup of the infancy of the planet.

But completing the set of nucleobases that make up life today, in addition to other molecules found in the analyzed space rock samples, is one more opportunity for those trying to understand how life began.

“This is adding more and more pieces; now meteorites have been found to have sugars and bases,” said Dworkin. “It’s exciting to see progress in making the fundamental molecules of biology from space.”

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