Asteroids and meteorites may have delivered the building blocks for life on Earth

Samples from the asteroid Ryugu revealed all five genetic nucleobases, suggesting the building blocks for life existed in space and may have been delivered to early Earth.

(CN) — Scientists analyzing samples from the asteroid Ryugu discovered the presence of all canonical nucleobases — the essential building blocks of life — strengthening the case that life’s ingredients may have actually come from space.

In a new study published Monday in Nature Astronomy, a group of nine researchers, many of whom are affiliated with the Japan Agency for Marine-Earth Science and Technology, or JAMSTEC, found the asteroid contained all five nucleobases used in modern genetic material: adenine, guanine, cytosine, thymine and uracil.

The team examined pristine asteroid samples collected from the carbon-rich asteroid Ryugu by a Japan Aerospace Exploration Agency, or JAXA, spacecraft. JAXA set out for Ryugu in late 2014, successfully landed in the summer of 2018 and returned to Earth with the samples about two years later.

Researchers initially subjected the samples to water and hydrochloric acid extractions, followed by various advanced chemical techniques that revealed the presence of all five nucleobases, which have become a focus in cosmochemistry and astrobiology because of their essential roles in biochemistry and prebiotic chemistry.

A unique result showed that the purine-to-pyrimidine base ratio is related to ammonia abundance, which suggests a previously unidentified chemical pathway for nucleobase formation.

The findings highlight that some of the building blocks needed for life are not distinctive to Earth and may have existed in the early solar system before life appeared on the planet, potentially contributing to the chemical processes that led to life.

In an email to Courthouse News, Toshiki Koga, a postdoctoral researcher at JAMSTEC’s Biogeochemistry Research Center, wrote that, until recently, nucleobases were found in only trace amounts in extraterrestrial materials and never all five at once.

“Because of this, they were not considered a major factor in discussions about the origin of life,” Koga said. “Our recent studies suggest that all five nucleobases can occur in extraterrestrial materials, indicating that these molecules may be more widespread in the solar system than previously thought and could have been an important source of organic molecules delivered to the early Earth.”

All five nucleobases were also detected in samples from previous studies of other near-Earth objects, such as the asteroid Bennu and the Murchison meteorite, as mentioned in the study. But the Ryugu samples’ nucleobase contents greatly differed from those of samples collected from the asteroid and the meteorite.

The Ryugu samples, Koga said, were collected directly in space and carefully preserved to avoid contamination.

“Meteorites found on Earth can be altered by the atmosphere, water and microorganisms after they land, which can make it harder to determine whether some molecules formed in space or on Earth,” Koga said.

The differences, he added, help scientists understand how organic chemistry varies across small bodies in the solar system, revealing how diverse chemical environments influence the formation of organic molecules.

After the study, a lingering question for the researchers now is how nucleobases formed in early solar system materials.

“Our results suggest a possible link between nucleobase composition and ammonia, and future studies, including meteorite analyses and laboratory experiments, will help test this idea,” Koga said.