Evidence piles up that building blocks of life on Earth came from space

(CN) — Scientists have found more evidence that the basic building blocks of life fell to earth via carbon-rich meteorites.

A team of researchers led by Dr. Yasuhiro Oba of Hokkaido University in Japan studied three carbon-rich meteorites — the Murchison, Murray and Tagish Lake meteorites. In a paper published in Nature Communications on Tuesday, the researchers detail the discovery of a number of previously unidentified pyrimidine nucleobases, ingredients of DNA and RNA. The researchers believe that the compounds may have been generated by photochemical reactions in space. The compounds may have "contributed to the emergence of genetic properties for the earliest life on Earth," according to the paper.

Scientists have, for years, hypothesized that DNA and RNA evolved from chemical compounds brought here by meteorites which crashed into ancient earth. In 2019, researchers found ribose and other bio-essential sugars in two different meteorites, including Murchison. They had previously found amino acids and three nucleobases.

"Prior to this study, researchers had only identified three nucleobases in meteorites that are found in DNA and RNA in life on Earth," said Dr. Daniel Glavin, an astrobiologist with NASA who worked on the paper, in an email. "The other two pyrimidine nucleobases found in biology, thymine and cytosine, had not been found in meteorites. In this study, we were also able to identify these missing nucleobases in meteorites, so we now know that the complete set of nucleobases used in DNA and RNA in life are also present in meteorites."

He aded: "This discovery further bolsters the theory that the chemical building blocks necessary for origin of life on Earth were delivered from space."

Dr. Yoshinori Takan with the Japan Agency for Marine-Earth Science and Technology, who also worked on the paper, agreeed.

"Thinking about the origins of life, that’s a very big issue," he said.

A number of molecules the researchers found in the meteorites remain unidentified.

The most intriguing findings, perhaps, are still to come. An unmanned Japanese space probe, the Hayabusa2, returned to Earth in December 2020 after surveying and collecting samples from the near-Earth asteroid 162173 Ryugu. The OSIRIS-REx, a U.S. probe, is scheduled to return to earth in September 2023 with samples of the Bennu asteroid.

Researchers hope to learn more about the origins of life from studying the newly collected samples, which are "pristine extraterrestrial materials that have not been significantly compromised by terrestrial contamination," the study says. The samples, the authors hope, "will provide us with important insights into the evolution of extraterrestrial organic molecules, and potential clues regarding the origins of life on Earth."

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