Life from meteors?

Some of the major building blocks for complex biological molecules may have arrived from the solar system or beyond, according to a new study. The evidence shows up in shards from the Murchison meteorite, which landed Down Under in 1969.

The idea that complex prebiotic chemicals could have come from space isn’t new. Other teams have shown that other biologically important acids hitched a ride on the Murchison meteorite. The smoking gun: The acids were enriched with the isotope carbon-13, compared with the same acids in terrestrial organisms.
Meanwhile, researchers have tested fragments from various meteorites for so-called nucleobases. These combine to form nucleotides, which in turn form DNA and RNA. The ultimate questions: Did these two biological heavy hitters form strictly from homegrown ingredients? Or did some of the more-complex biochemical middle-men arrive, premixed, via comets and asteroids?

The evidence has been ambiguous; others have shown how the nucleobases could be present either from contamination after the meteorite struck Earth or as a byproduct of the techniques used to detect the nucleobases in the lab. A team led by Zita Martins of Britain’s Imperial College analyzed two nucleobases found in the Murchison meteorite – uracil and xanthine – and paid close attention to carbon-13. The team found that Murchison nucleobases also were heavy on carbon-13, compared with their terrestrial counterparts, indicating an extraterrestrial source. The results appear in the current issue of Earth and Planetary Science Letters.