Planetary science: Building blocks of DNA detected in meteorites

Pyrimidine nucleobases that are necessary for building DNA or RNA may have been delivered to Earth by carbon-rich meteorites, suggests a paper published in Nature Communications.

Two types of chemical building blocks, or nucleobases, are needed to form DNA and RNA. These are the pyrimidines, which include cytosine, uracil and thymine, and the purines, for example guanine and adenine. Thus far, only purine nucleobases and uracil have been identified in meteorites. However, the detection of pyrimidines in laboratory experiments simulating conditions in the interstellar media — the space between stars — has led to speculation that meteoritic delivery may have occurred.

Using state-of-the-art analytical techniques optimised for the small-scale quantification of nucleobases, Yasuhiro Oba and colleagues analysed 3 carbon-rich meteorites; the Murchison, Murray and Tagish Lake meteorites. In addition to compounds that have previously been detected in meteorites — such as guanine, adenine and uracil — the authors identify various pyrimidine nucleobases, such as cytosine and thymine, for the first time at concentration levels up to parts per billion. These compounds are present at concentrations similar to those predicted by experiments replicating conditions which existed prior to the formation of the solar system.

The authors conclude that these findings suggest that such compounds may have been partly generated by photochemical reactions in the interstellar media, which later led to their incorporation into asteroids as the solar system formed. Their eventual delivery to Earth by meteorites may have subsequently played a role in the emergence of genetic functions for early life.