Decoding the origin of Life on Earth

Decoding the origin of Life on Earth

All of the nucleobases (bases in DNA & RNA) found in three carbonaceous meteorites

Nucleobases (bases in DNA & RNA) are the key building block for organic molecules. Presence of organic molecules in extraterrestrial environments has been widely accepted. Despite extensive studies on the formation of organic molecules in various extraterrestrial environments, it still remains under debate when, where, and how such molecules were abiotically formed. A key molecule to solve the problem, hexamethylenetetramine (HMT) was not confirmed in extraterrestrial materials despite extensive laboratory experimental evidence that it can be produced in interstellar or cometary environments.

All DNA and RNA, which contains the instructions to build and operate every living being on Earth, contain five informational components, called nucleobases. Nucleobases belong to classes of organic molecules called purines and pyrimidines, which have a wide variety.

Until now, scientists scouring extraterrestrial samples had only found three of the five. It remains a mystery why more types haven’t been discovered in meteorites so far.

Recently a team of scientists from USA & Japan, led by Yasuhiro Oba, Associate Professor (Hokkaido University, Hokkaido, Japan) identified the final two nucleobases that have eluded scientists. They confirmed the presence of HMT in three different meteorites. Scientists have confirmed the presence of a prebiotic organic molecule (hexamethylenetetramine C6H12N4; HMT) in three different carbon-rich meteorites. HMT may have been used as key molecule in the formation of organic compounds and to build other organic molecules, including some used by life. The discovery validates theories of the formation of organic compounds in extraterrestrial environments.

A Chunk from this rock (2g) (a piece of the meteorite that fell near Murchison, Australia, in 1969) contains two crucial components of DNA and RNA now identified for the first time in an extraterrestrial source (Credits: NASA)

Danny Glavin, a co-author of the paper at NASA’s Goddard Space Flight Center in Greenbelt, Maryland told that “We now have evidence that the complete set of nucleobases used in life today could have been available on Earth when life emerged,”.

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. (Credits: NASA Goddard/CI Lab/Dan Gallagher)

Chemical reactions in asteroids can make some of life’s ingredients, which could have been delivered to ancient Earth by meteorite impacts or perhaps the infall of dust.

Photo Source: Irrera, S., 2006: Structural and electronic properties of chiral molecules on surfaces. PhD thesis, Padis La Sapienza,

1.     Oba, Y., Takano, Y., Furukawa, Y. et al. Identifying the wide diversity of extraterrestrial purine and pyrimidine nucleobases in carbonaceous meteorites. Nat Commun 13, 2008 (2022).

2.    Oba, Y., Takano, Y., Naraoka, H. et al. Extraterrestrial hexamethylenetetramine in meteorites—a precursor of prebiotic chemistry in the inner solar system. Nat Commun 11, 6243 (2020).

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