Have no doubt about it, we are seeing the science equivalent of a massive battle flotilla forming off the shores of Normandy. NASA is about to claim the field in “Origin of Life” theories. Their Allan Hills foray, the Meteorite ALH84001 paper of August, 1996, was turned back by a self-preserving barrage from other first cell theorists. Thus humbled, NASA hunkered down and aimed their superior weaponry, space exploration, at the soft underbelly of their detractors, Mars.
Recall that the argument for life on Mars, and the associated possibility of Mars seeding life to Earth, was ripped apart by claims that Meteorite ALH84001 (from Mars) had been contaminated by Earth microbes after it got here—an argument that is difficult to disprove, unless you find a similar rock on Mars. That would be a homerun for Curiosity, and that homerun will put NASA in the driver’s seat of first cell research. Massive defections from the camps of the other theories will soon follow.
Assume they will find evidence of Martian microbes, because they will; does that mean Mars seeded life to Earth? My guess is no. My logic is that there are three types of fragments from Mars that could become meteorites on Earth. For sake of argument, let’s say all three had living microbes in them when they left Mars.
Type 1 is your “normal” size meteor, big enough to heat to very high temperatures as it careens to Earth—all of its microbes fried before contact.
Type 2 is dust so fine that it will flow to Earth without heating. These however will experience temperatures so cold, I mean really cold, like near absolute zero, that all microbes will be fragmented crystals before they get here.
Type 3 is so huge that it will cause a cataclysmic event when it enters the Earth’s atmosphere. Oddly, this one might deliver live organisms to Earth.
Research has shown that microbes permeate Earth’s crust from the surface to depths of a mile or more. Assume the same was once true of Mars. Then a major fragment of Mars could, in theory, burn through our atmosphere while its center remains insulated from the high temperatures experienced on its surface. Microbes at its center could survive the trip much as our astronauts survive reentry, thanks to the insulating tiles on the surface of their spacecraft. Such a meteorite might deliver life forms to Earth, but I’m not sure such a large Martian meteorite ever came to Earth.
But what is Curiosity finds live cells? These may exist, but to find them might require drilling a substantial depth into the Mars crust. If we were to get lucky and find live cells, I expect we would learn they are of the same DNA model as life on Earth. Would that prove Earth was seeded from Mars?
Again, I think not.
Mars life being a sister to Earth life would imply three possibilities:
Theory 1: Earth was seeded from Mars or visa versa. Based on my arguments above, this would be unlikely, although a meteorite from Earth would face less atmospheric cleansing than one coming here from Mars. Unfortunately, a life-bearing meteorite from Earth would hit Mars too late, long after its benign, life sustaining environment had cooked away.
Theory 2: Life always follows the same chemical path to emergence, i.e. there just is no other way for life to form than the way it formed on Earth, hence all life in the universe will always be sisters although formed completely independent from each other. However, our DNA is said to have a lot of unnecessary stuff in it, I assume even if life followed the same path to emergence, it would have different unnecessary stuff or no unnecessary stuff, but is very unlikely to have the same unnecessary stuff, hence it would not be exactly the same as our DNA.
Theory 3: All life forms, in our galaxy at least, came from the same source and therefore are our genetic sisters. This is panspermia, and I believe Curiosity will make the first step to proving it is correct.
I even suspect that the life spores were spread concurrent with emergence of the universe itself, in the Big Bang.