Nucleobases From Space

In a bid to answer a decades-old question, a multi-institution team has presented the strongest evidence yet that nucleobases, the building blocks of DNA, could have been made on meteorites in space and delivered to a primordial Earth (Proc. Natl. Acad. Sci. USA, DOI: 10.1073/pnas.1106493108). Researchers have been finding amino acids and nucleobases—the molecules of life—in meteorites for some time. While they’ve confirmed the amino acids’ extraterrestrial origins, purine and pyrimidine nucleobases found in the space rocks could always be explained as earthly contamination. Michael P. Callahan of NASA’s Goddard Space Flight Center and colleagues have now analyzed a dozen meteorites found in Antarctica and elsewhere with high-resolution liquid chromatography-mass spectrometry. In two meteorites they detected traces of purines that are rare or absent in biology. The team didn’t find those exotic purines in ice and soil found near the meteorites. But laboratory reactions of ammonia, water, and hydrogen cyanide, which are all present in meteorites, produced the entire purine suite. The team is continuing to make measurements in additional meteorites, Callahan says.