I've been disappointed that the Mars rovers never brought a microscope to Mars to, well, look for microbes directly.
Now I realize they didn't have to.
Because: in the same way that clams or grasses grow together in clumps, so do many types of bacteria. We don't see an isolated bacterial cell. Partly this is because many grow so rapidly (E. coli has a doubling time of 20 min. in the lab under ideal conditions). Under a microscope you don't see an individual bacterium; you see many of them:
This is Bacillus subtilis
, a common rod-shaped bacterium.
In the Mars rock supposed to contain a bacterial fossil, you don't see clusters of bacteria. You see one, perhaps two:
At first glance, it just doesn't LOOK like a bacterial fossil.
Another reason you don't need to bring a microscope to find evidence of microbes is because the clusters they make are called, for example, biofilms, and they can easily be seen by the naked eye. Recently, I've been dealing with plugged sinks, and when you pump the plugger, little black flecks some up in the backwash. What is this? A biofilm! Layers of bacteria growing on the inside surface of the water pipe. You have a biofilm on your teeth (ick), and coating the insides of your intestines.
Individual bacteria may not fossilize, but biofilms would leave a tell-tale trace of life. This is because an organism is not just an ugly bag of mostly water. No, it is a CONCENTRATED ugly bag of mostly water. A human being is a bag of chemicals entirely distinct from its surroundings. Humans are full of metal ions - calcium in bones, iron in blood. And these concentrated levels of metals are entirely different than, say, the masonite walls or the stone floor around and beneath us.
And even if the cells don't fossilize, the metals remain.
Here is an image of the analysis of metals (I think it was mass spec) from a dinosaur fossil.
This is from Wogelius et al. 2010 Science 333: 1622. (They were looking at metals associated with different pigments to see what color this dinosaur might have been.) Biofilms would leave a tell-tale layer of concentrated metal on the side of a rock. It might not be calcium, it might not be iron or copper, but it would be SOMETHING. And it would likely be only on one side of the rock (as biofilms only form on the insides of pipes, not the outside). (Biofilms often have a distinctive color, the way that the film on pipes is dark brown/black, and the way that ick on your teeth is whitish-yellow. Bacteria come in different colors, donchya know.)
But there haven't been any reports of this sort of thing. Which makes me think that no one has found any. (Even if they didn't make the connection with biofillms, geologists would remark on the amazing concentration of metal ions on one side of a rock and not on any others, or on some rocks and not on others.)
Thus: No evidence of metal concentration, thus no biofilms, thus no bacteria on Mars. (And it doesn't matter that we've only looked at a few isolated places on Mars - because life SPREADS.)
Thus: I can safely and sadly conclude that there never was life on Mars.
On a related note, we can also conclude that life doesn't exist on Mars today. Because we'd see evidence of biofilms (even if it were deep underground, with erosion and churning of rocks, we'd have seen it by now.) Bacterial don't have to be fossils to leave metallic evidence of biofilms.
This is a sad day, then, for me. The end of a dream (the way that some men express sadness when they discover that they never will become a professional baseball player). A dream that started in earnest July 20, 1976, when I woke up at 8 in the morning to watch the Viking I probe land on Mars. And has now ended today, January 6, 2013. I don't care how much running water there was from time to time on Mars. There is not now nor was there ever life on Mars.
Great lj overmind: Yeah or nay?