If We Find Martian Life, Will We be Able to tell it Didn't Originate on Earth?

It's been said that finding life on Mars (even microbial life) would be a milestone for us humans, because if life can evolve independently on two different planets in the same solar system, then that will indicate that life could be abundant throughout the rest of the universe.

That all makes sense, but my question is this: What tests can be done to that Martian life that will prove that it is indeed of Martian Origin, and not something that has come from Earth (hitching a ride aboard a meteor, for example). There are 30+ meteorites that have been found on Earth (and probably more unfound) that have been proven to have originated from Mars, including the famous ALH84001 that may or may not contain fossils of microbial Martian life (the jury is still out). Is it possible that a similar meteorite originating from Earth millions of years ago, packed with life, could have ended up on a dead Mars, seeding that planet with life from Earth? Would we be able to identify that life as originating here?

If the above scenario is possible, it seems to me that if we do find life on Mars, and we can't be certain it developed there independent of Earth, then we can't say that "if life is found in two places in one solar system, then it must be universally abundant". Some test will need to be done that proves any potential Martian life is truely an independent life form before that claim could be made.

I suppose another possibility is that life in the solar system only developed on Mars, and the dead Earth was seeded by those Martian meteorites, or even that life started only on some comet that seeded both the Earth and Mars. All of these scenarios point to the idea that the processes that led to "life" only happened in one place in the solar sytem in the past 4.5 billion years, and that life can truly be considered a unique entity.

For the record, I personally feel that life is universally abundant, but what I feel is irrelevant in the eyes of science. We need proof.

[edit on 14-6-2007 by Soylent Green Is People]

I have heard several scientist state that life on Mars probably originated from Earth. So with this theory in mind, does that mean ANY life ANYWHERE in the Universe may have come from Earth? After all, meteorites could have been leap frogging all over the place for the last 13 billion years, so who knows where life originated.

To me, the important question is not where said life originated, but the fact that it was able to sustain itself, and propagate its species. This is exciting because a single cell creature that hitched a ride 1 billion years ago, ended up on a planet far, far away…could mean that it has evolved into a complex conscious creature just like us – or better!

The process you are both describing - where life from one planet is transfered to another by a meteoroid, for example - is an example of what astrobiologists call panspermia, and while certain scientists may have their pet theories, WatchNLearn, there is no solid proof that life ever existed on Mars in the first place, so that theorizing is purely academic. Personally, I think that there probably was life on Mars at some point in the past - although the case for any extant life, even bacteria, is much more dicey - but so far there's no particularly solid evidence to support that belief. I'm just going to have to wait....

As for Soylent Green Is People's question in the OP, I don't know if there is any "test" we could do to Martian life to determine with any particular certainty that it didn't migrate from Earth, or that early Martian life wasn't transported to Earth via meteor. DNA is a pretty interesting substance, and even if we discover Martian life which has DNA at all it wouldn't necessarily mean that said life came from Earth/later went to Earth. We just don't - and won't, not for the foreseeable future - have a large enough sample size in our "study" of life to make any informed conclusions.

That said, if we find life on Mars and it is significantly different from life on Earth - it is based on something other than DNA (or RNA, DNA's cousin), or has a DNA-like structure but is arranged in a triple- or quadruple-helix instead of a double-helix (like DNA), or it uses either 2, 6, or more base pairs of Amino Acids to form the base pairs of its DNA - well, you get the picture.

IF - and only if - life on Mars (or www.solarviews.com... , or Titan, or any of the other planets/moons we think might be capable of supporting life) is significantly different from life on Earth, then we will be able to say with relative certainty that said life evolved independently. Otherwise it will likely be a question which plauges scientists - and space dorks like me - for a long, long time.

Through DNA testing, you could probably prove that a given life form is native to Earth. Proving that something is not earth life, though; I don't know any way it could be done with 100% certainty.

If the life form was so completely different than anything encountered, like those who suggested life without DNA/RNA, or silicon-based life, or something totally bizarre, then we could be virtually certain it was not an earth species. Still, we wouldn't know for certain.

If the life form was actually found on Mars AND was fundamentally different from earth life, I'd say that is quite conclusive. If it obeyed only one of those two requirements, there would be doubt. Unusual life found on earth could be natural; indeed, Occam's razor would suggest this. Any life found on Mars, though, I would tend to believe was Martian in origin, rather than seeded via panspermia or other methods.

Well, I suspect we will need to do DNA testing and such, and even then we can't be sure the life originated on Mars unless it is a form of life that's so different than our own. But that would require a mission which brings a sample of that life back to Earth, or a mission that takes a sophisticated lab (and maybe humans) to Mars.

Scientists have been saying that finding life on Mars would prove that life could be abundant in the universe, but the way I see it, even if we find life soon, we have no easy way to prove that it developed completely independant of Earth.

The Mars Phoenix mission will be landing near the Martian ice caps next year and the Mars Science Laboratory will be roving the planet starting in 2009. If one of those two missions finds life, I'm sure some people will be quick to claim that this means the universe must be teeming with life (which, as I said in an earlier post, I think life does exist out there somewhere) but I don't think those signs of Martin life will be the proof positive of this until we can actually analyze that life very closely.