If I understand this correctly, asteroids, comets, and meteors that hit the earth DO CONTAIN cosmic debris, including water and various elements.
The aforementioned meteor found in Antarctica was preserved on the frozen continent. The meteor from Mars left that planet after some form of catastrophic collision. The question concerning the bacteria is whether it is from earth or from Mars.
Scientists have studied the meteor and found the meteor is from Mars based on what we've learned about the planet. Because science cannot be 100% sure--by the very definition of science always learning--it is presented with an assumption (of a certain percentage) that the bacteria is Martian.
If the bacteria proves to be martian, the question scientists then ask is, how much of earth's life started on earth and how much came from some other planet, moon, star, or wherever? How much of earth's water came from earth and how much came from an impact from comets?
Bacteria does not mean there were Martians, just that Mars contains bacteria. It also makes it clear, if proven with greater certanty that bacteria is martian, that bacteria, viri, viroids, etc. could travel certain distances in so-called "lifeless" space.
Correct me if I'm wrong on anything here...
Well, I'll tell you up front, I'm very skeptical of all of this, so you know. But, I really am curious what convinces these guys that this rock is from Mars...
Seems like a big assumption.
That is a good overview.
The main (initial) reason for the assumption that the meteorite (and a number of others) were from Mars was the location -- Antarctic. Polar impact on Earth was (for some reason, I dunno this stuff) considered to mean a Martian origin.
The composition of rocks from space shows affinities, implying common origins. But there wasn't much else to go on. The way these supposed Mars rocks got here was that they were blasted out by large impacts on Mars. :')
There were words of caution regarding the claims of fossil cellular structures in the rock, way back at that time. I remember reading secondhand that the whole thing was a piece of theater intended to push support for human missions to Mars, and that's where the bandwagon ended up.
Anything sufficiently energetic to kick rocks up out of Mars' gravity well might well be expected to wipe out any kind of fossil evidence. And if that wouldn't do it, ripping through the Earth's atmosphere would. :')