If you want to see the offspring of extraterrestrial interference in Earth evolution, you don't have to break into the X-files or start watching late night crazy-person public access. You could be looking at one in the mirror.
Early in Earth's history the surface suffered a heavy hail of meteorites. This is usually bad news for any lifeforms in the vicinity (if you don't believe me, just ask a velociraptor), but since even DNA was only a gleam in the ocean's eye at the time the space-rocks weren't a setback - in fact, they may have delivered vital ingredients to the rich pre-life soup on the surface.
There are those who say that the evolution of life is impossible, which only proves that for all their talk of eternity and hellfire they don't really understand how long a billion years is or the power heat and chemicals can have. From the evolutionary point of view, the idea of off-planet assistance isn't just possible, it's sensible - after all, a wider galaxy has a better chance of coming up with the correct chemical cocktail than just one otherwise unremarkable mudball.
Now scientists have proof that this is possible. A collaboration between various US and European institutes has proven the presence of vital nucleobases in the Murchison meteorite, an extraterrestrial rock fragment which impacted Earth in 1969. Nucleobases are the very binary bits of DNA, the base pairs that make up the vital genetic information.
Uracil and Xanthine are the two most exciting components detected. You might not recognise them from the famous GATTACAn roster of Guanine, Adenine, Cytosine and Thymine; this is because Uracil is Thymines stand-in when RNA is created, and Xanthene is a mutated form of Guanine. So for those of you who like things in headline form: "Mutant DNA from Alien Space Rock."
These bases are unquestionably alien - for one, the rock-chemicals are equally left and right "handed" (a property of the physical structure of the chemicals), while the Earth-borne biological equivalents are either one or the other(sugars are right-handed, amino acids are left-handed). Even more fundamentally, the carbon atoms that make these chemicals organic at all are a space born isotope, the not-so-unlucky Carbon-13, while life on Earth is based on Carbon-12.
Strikes of such substances early in evolution may have played a vital role in the development of Earth biology - and with these precious particles literally falling out of the sky, the odds of life off-planet seem better than ever.
Posted by Luke McKinney.