what exactly is a trace of bacteria?
would that be a carbon molecule?
link please.
I have seen plenty of Article re this, just a quick Google should give you a couple ie:
http://www.unisci.com/stories/20013/0730011.htm
But like I said the problem with volcanic eruptions and previous meteor hits, it can easily argued that those bacteria found(Including the ones inside meteors) could have originated from earth. Its even proven via computer models that we could be seeding life on Mars and beyond. So finding life on Mars would not be a 100% proof that life originated off planet earth. Also the fact that life on earth came in many forms not only carbon based, shows that chemical composition could not be proof either.
In other words the only 100% guaranteed proof that life originated is if ET sends us an undisputed please call me or come park on planet Earth for some good old fashion game hunting.
And this coming from someone that recons there is no way in hell that planet Earth is the only place in this universe where life has started, hell I would even go so far as to say that our planet is still seen as a newborn in the scheme of things. Some planets out there had like 5-7 billion years head start.