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Could the earliest building blocks of life have come from space?

It might sound outlandish, but it’s possible that some of the earliest components of life were carried to Earth on a meteorite. Recent research has shown that all five of the basic building blocks of DNA have been found in meteorites.

To be clear, it isn’t that DNA has been found on a rock from outer space. Rather, the result is that each of the five basic compounds which make up DNA and RNA, called nucleobases, have been found in meteorite samples. Previously, only three of these nucleobases had been found on meteorites, but recent research has identified the final two.

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Conceptual image of meteoroids delivering nucleobases to ancient Earth. The nucleobases are represented by structural diagrams with hydrogen atoms as white spheres, carbon as black, nitrogen as blue and oxygen as red.
Conceptual image of meteoroids delivering nucleobases to ancient Earth. The nucleobases are represented by structural diagrams with hydrogen atoms as white spheres, carbon as black, nitrogen as blue, and oxygen as red. NASA Goddard/CI Lab/Dan Gallagher

“We now have evidence that the complete set of nucleobases used in life today could have been available on Earth when life emerged,” said one of the authors, Danny Glavin of NASA’s Goddard Space Flight Center, in a statement.

The two outstanding nucleobases were cytosine and thymine. These were harder to identify than the other three nucleobases (adenine, guanine, and uracil) because they have a more delicate structure which is easily broken down by the process of collecting and analyzing samples. NASA describes the traditional method of analysis of these samples as making a “meteorite tea,” in which small samples from a meteorite are put into hot liquid so that the samples are extracted and the watery solution can be studied.

“We study these water extracts since they contain the good stuff, ancient organic molecules that could have been key building blocks for the origin of life on Earth,” explained Glavin.

But the two remaining nucleobases required a more careful method to be identified, using cool water and a more sensitive analysis process. “This group has managed a technique that is more like cold brew than hot tea and is able to pull out more delicate compounds,” explained another co-author, Jason Dworkin. “I was amazed that they had seen cytosine, which is very fragile.”

Whether the ingredients for life did actually come to Earth on a meteorite is still an open question. Life could also have developed from the primordial soup of a very young planet Earth, from the interactions of organic compounds. But this research opens up more possibilities for future research into the topic.

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

The research is published in the journal Nature.

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