If you hadn’t heard recently a story broke on numerous websites that some researchers had found ” building blocks of life” in a meteorite. Numerous headlines stated that we were aliens and other such things to grab the attention of readers. I’ve never found science journalism to be particularly great at explaining things so I thought I might clarify things a little. Several researchers from around the world ( Imperial College London, Nasa Goddard Space Flight Centre, Radboud University Nijmegen etc.) extracted and analyzed a 15 g sample from the interior of the Murchison meteorite.
They crushed it and going through an extensive purification process eluted out any organic compounds they could find. Then using mass spectroscopy ( a way of determining what a compound is by ionizing it and firing it against a detector and determining it’s time of flight) they determined samples of both uracil and xanthine were present in the meteorite. This actually fairly cool since uracil is a component of RNA and xanthine is an intermediate in the biosynthetic pathway to guanine, another nucleobase found in both DNA and RNA.
It was determined through isotope analysis of these samples that significant proportions of the carbon atoms found in them were of carbon 13 indicating that the molecules likely formed extraterrestrially since carbon 13 is rarely found on earth.
A damn cool story but it’s not like they’ve found incontrovertible evidence that earth was seeded from the heavens by aliens. It just means that life on this planet may have been partially jump started by these biological precursors from the stars, which is still fairly cool I think.
Incidentally, xanthine is one of the intermediates in the pathway that leads to caffeine. Looks like it’s always had a role in getting things going 
Reference:
Martins, Z. et al. 2008. Extraterrestrial nucleobases in the Murchison meteorite. Earth and Planetary Science Letters 270: 130-136
