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How strong is the claim by Steven Benner that Earth life likely originated on Mars and was brought to this planet aboard a Meteorite?

• Context: http://www.space.com/22577-earth-life-from-mars-theory.html Evidence is building that Earth life originated on http://www.space.com/47-mars-the-red-planet-fourth-planet-from-the-sun.html and was brought to this planet aboard a meteorite, said biochemist Steven Benner of The Westheimer Institute for Science and Technology in Florida. An oxidized form of the element molybdenum, which may have been crucial to the origin of life, was likely available on the Red Planet's surface long ago, but unavailable on Earth, said Benner, who presented his findings today (Aug. 28; Aug. 29 local time) at the annual Goldschmidt geochemistry conference in Florence, Italy. "It’s only when molybdenum becomes highly oxidized that it is able to influence how early life formed," Benner said in a statement. "This form of molybdenum couldn’t have been available on Earth at the time life first began, because 3 billion years ago, the surface of the Earth had very little oxygen, but Mars did. It’s yet another piece of evidence which makes it more likely life came to Earth on a http://www.space.com/18019-martian-meteorite-black-glass-photos.html, rather than starting on this planet." Organic compounds are the building blocks of life, but they need a little help to make things happen. Simply adding energy such as heat or light turns a soup of organic molecules into a tarlike substance, Benner said. That's where oxidized molybdenum comes in. Inserting it or boron, another element, into the mix would help organics make the leap to life, Benner added. "Analysis of a Martian meteorite recently showed that there was boron on Mars; we now believe that the oxidized form of molybdenum was there, too," he said. Another point in Mars' favor is the likelihood that the early Earth was completely covered by water while the ancient Red Planet had substantial dry areas, Benner said. All of this liquid would have made it difficult for boron, which is currently found only in extremely dry places, to form in high enough concentrations on Earth when life was first evolving. Further, Benner added, water is corrosive to RNA, which most researchers think was the first genetic molecule (rather than DNA, which came later). No indigenous Red Planet organisms have ever been discovered. But it is possible that http://www.space.com/17135-life-on-mars.html — if it ever existed — may have made its way to Earth at some point, many scientists say. Some microbes are incredibly hardy, after all, and may be able to survive an interplanetary journey after being blasted off their home world by an asteroid impact. And orbital dynamics show that it's much easier for rocks to travel from Mars to Earth than the other way around. Wherever Earth life originated, Benner is glad it put down roots on our blue planet. "It’s lucky that we ended up here nevertheless, as certainly Earth has been the better of the two planets for sustaining life," Benner said. "If our hypothetical Martian ancestors had remained on Mars, there might not have been a story to tell."

• Answer:

  Brenner's hypothesis here is sound, but it's just one hypothesis for the origin of an RNA world, which is just one of the models for the origin of life. Basically, Brenner's experiments found that there are many ways for RNA to form from abiotic precursors. However, most of the time, they end up as a black tar, no good. Adding borate improves the chances of successful combination, and adding molybdate increases the chances to very good levels. It's highly unlikely that borate could have existed on the early Earth, given that nowadays it's only found in evaporites. Molybdates could not have existed on the early Earth because there was no free oxygen. But Mars had both those chemicals, therefore this lab experiment could have occurred naturally there. So far, so good. In my opinion, the rest is too much conjecture. I personally find the idea of meteorites "seeding" the Earth to be a bit far-fetched. Sure, you can find traces of organic chemicals on meteorites in space, but what are the chances of these molecules surviving a meteor crash? I've been to several meteor craters and have seen the effects on the geology and geomorphology. I think just the heat from the crash itself would be enough to get rid of any organic chemicals (but I have no citation for this). But even if the organic molecules survive the meteorite ride to Earth, an RNA world is not the origin of life. RNAs are, at best, self-replicating autocatalytic molecules. But without a system of metabolism, you don't have life just yet. These Mars panspermia models don't have a mechanism for the origin of metabolism, while we know that metabolic mechanisms can arise naturally on the early Earth, as can proto-cell membranes. (see: http://bioteaching.wordpress.com/2011/05/27/the-origin-of-life-and-of-the-atmosphere/). So, at best, we have 50% of the components of life arising on Mars (the raw genetic part), unless you also come up with the metabolism too.