A trio of unique meteorites show evidence for fundamental building blocks of life, two of which astronomers had not previously identified in space rocks.
In a new paper published Tuesday in the journal Nature Communications, Japanese scientists describe how they analyzed samples of these meteorites. The researchers looked at three different meteors gathered in different locations across a 70-year span. They found the presence of nucleobases, one of three components that form a molecule called nucleic acid, which possesses the genetic information for all living organisms.
The team looked at two samples from the Murchison meteorite, which fell in Australia in 1969. They also looked at Tagish Lake meteorite fragments, which fell in Canada in 2000, and specimens of the Murray meteorite, which fell in the United States in 1950.
Leading the study is Yasuhiro Oba, associate professor at the Institute of Low Temperature Science at Hokkaido University in Japan. In 2019, Oba helmed a pioneering study that found nucleobases could have formed in the interstellar medium, the region of outer space beyond the Solar System that separates star systems from each other.
“In the present study, such biologically important molecules were detected in carbonaceous meteorites, meaning that they would also have been delivered to the early Earth before the onset of life on the Earth, and may play some roles for the emergence of genetic functions in molecules and the origin of life,” Oba tells Inverse in an email.
What did they find? — The team used a technique called mass spectroscopy to detect the nucleobases. They were able “to identify a target molecule among hundreds of thousand molecules in a meteorite,” Oba says.
Scientists classify nucleobases into two categories. One is called pyrimidine bases, which include cytosine, thymine, and uracil. These molecules have a hexagonal ring with two nitrogen atoms in their structure, and without them, the iconic double helix structures of DNA and RNA cannot be made.
According to Oba, the new study found all three pyrimidines in Murchison meteorites, whereas previous studies had only detected uracil. This means a “diversity of meteoritic nucleobases” could have reached a young Earth and been the building blocks of DNA and RNA, according to the study.
And these building blocks appear in space rocks that had different experiences.
The other type of nucleobase, called purines, was also detected at a high quantity in the Murchison meteorite and not found in the surrounding soil, meaning that this building block of life came from space and not through exposure on Earth. The researchers also detected purines in the other two meteorites, but to a lesser degree. This suggests that the parent bodies of the Tagish Lake and Murray meteorites went through different processes than the space rock that bore the Murchinson meteorite.
What’s Next? — The next step is seeing how these nucleobases formed on these meteorites in the first place, which is beyond the scope of this study.
But new samples retrieved from near-Earth asteroids could help us understand their formation better. Missions like Japan’s Hayabusa2 have already successfully returned samples from asteroid Ryugu, and the asteroid Bennu specimens snagged by NASA’s OSIRIS-REx mission are on their way to us now.
“I am very much looking forward to seeing what new discoveries we will make from Ryugu and Bennu,” study author Yoshinori Takano tells Inverse in an email.
Takano is the Deputy Director of the Biogeochemistry Research Center at the Japan Agency for Marine-Earth Science and Technology. He’s collaborating on Hayabusa2 and OSIRIS-REx, and hopes these missions will flesh out what is currently known about life’s deep-space origins.