According to a report from a European and American collaborative group of scientists interested in Earth and Planetary science, analysis of a meteorite suggests that organic compounds involved in the chemical reactions that produce the purines and pyrimidines that make up DNA and RNA may have already been present in the early solar system, reaching Earth through meteor bombardments and other contacts with extraterrestrial sources. The abstract of the article by astrobiologist Zita Martin and colleagues, reads as follows:
"Carbon-rich meteorites, carbonaceous chondrites, contain many biologically relevant organic molecules and delivered prebiotic material to the young Earth. We present compound-specific carbon isotope data indicating that measured purine and pyrimidine compounds are indigenous components of the Murchison meteorite. Carbon isotope ratios for uracil and xanthine of δ13C=+44.5‰ and +37.7‰, respectively, indicate a non-terrestrial origin for these compounds. These new results demonstrate that organic compounds, which are components of the genetic code in modern biochemistry, were already present in the early solar system and may have played a key role in life's origin."
See: Martins Z, Botta O, Fogel ML et al. Extraterrestrial nucleobases in the Murchison meteorite. Earth and Planetary Science Letters 2008;270:130-6.