Astrobiologists have long thought that the building blocks of life may have arrived on Earth via meteorites. They now may have proof of that idea. For the first time, scientists have discovered complex, biologically essential sugars in two meteorite samples (Proc. Natl. Acad. Sci. U.S.A. 2019, DOI: 10.1073/pnas.1907169116). The researchers analyzed sugars from three chondrites, or primarily rocky meteorites, and found detectable levels of ribose in two of the samples. They analyzed the carbon isotopes of their samples and found that the sugars were enriched in carbon-13, indicating that they originated extraterrestrially. It’s unclear why these two meteorites preserved sugars and the third did not, says Tohoku University geochemist Yoshihiro Furukawa, who led the study. One potential pathway for the formation of extraterrestrial sugars is the formose reaction, which creates complex sugars from simple precursors like formaldehyde. The researchers showed that a formose-like reaction carried out in the laboratory produced sugars in a proportion similar to that found in the meteorites. Furukawa says the detection of ribose in the meteorites lends support to the idea that biopolymers such as RNA on prebiotic Earth may have extraterrestrial origins.