From an article on Yahoo!, Life on Earth Started on Mars, say Scientists:

Prof Benner, from The Westheimer Institute for Science and Technology in the US, said: “The evidence seems to be building that we are actually all Martians; that life started on Mars and came to Earth on a rock.”

Speaking at the Goldschmidt 2013 conference in Florence, Italy, he said: “It’s lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life.

“If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell.”

Prof Benner said the element molybdenum was thought to be a catalyst that helped organic molecules develop into the first living things.

It is not known how life started, not here on Earth, or anywhere else.  We simply do not know.   All we have are speculations.  Thus it is not known whether or not molybdenum was a necessary element for its inception.  The logic is very simple–if you don’t know how a thing started, then you also don’t know what conditions and materials were necessary to getting it started.

That the good scientist extended his fallacious speculations to opine that it was a good thing we ended up here is nothing more than taking a flight of logical fancy, something akin to the tactics of hack science fiction writers.   Earth is not necessarily the better of the two planets for sustaining life, unless it is imagined that the life that arose on Earth is on the only life possible.  And the life that arose on Earth didn’t fashion the Earth to suit its needs, it fashioned its needs to suit the resources and environment provided by Earth.    Had some form of life arose on Mars, it too would have fashioned itself to suit the particular resources and environment provided by Mars.   And it would have had a story to tell, analogous to our own, but not remotely decipherable or meaningful to any life form except itself.   Just like ours. 

Prof Benner accomplished exactly what he intended with his speculative conclusions:  He got himself in the news, proving once again that scientists are just like every other form of the human species, prone to self-promotion and adulation seeking. 

And just like the scientists who reach their speculative conclusions on the climate of the whole Earth on the basis of about two centuries of evidence, or the scientists who proclaim the universe is comprised of thinly vibrating membranes only accessible in invisible dimensions, Prof Benner’s speculations will always remain just that.  His theory is non-falsifiable, so it doesn’t even rise to the level of hypothesis.  Even if we someday discover how life started on Earth, and it is proved that molybdenum was necessary to its inception, and it is clear that Earth did not have much of it on its surface at the time, it still would be nothing more than unprovable speculation to claim that it must have come from Mars.  

There is never any way to know for sure what happened billions of years ago.  Some of our speculations are more robustly grounded in the available evidence than are others, but in the end, all are speculations. 

The ranks of the scientific priesthood that has arisen to profit from the respect and awe with which scientists and scientific discoveries have been generally regarded in the modern age has back-filled with charlatans, mystics and shamans.  Scientific revelation happily replaced religious revelation as a source of ultimate truth starting about the time Galileo whispered, “But it moves”.  Now scientific revelation has come full circle, proffering explanations of the material world on evidence not much better than that available to a medieval priest.