Why did you launch the Beagle mission?
If you're asking people to believe an outstanding claim, like 'we've discovered life somewhere else', then the evidence you present has got to be equally water-tight. It's got to be 110 percent cast-iron proof. You can't do that by studying meteorites that have landed on earth because you're always going to get somebody who says to you, “They have been in the terrestrial environment, which is teeming with life. All you're doing is looking at terrestrial contamination.” Now, we could never prove that we weren't. Circumstantially, we could say that we weren't about the meteorites, but you can't absolutely prove it. So, what we were actually going to do with Beagle was to go back and repeat the experiments that we did on earth in the environment of Mars, where we could say, “Well, we built this spacecraft clean. It's not carrying any terrestrial microbiology, so anything we see on Mars is authentic.” Now, looking for fossils is one of these situations where beauty is in the eye of the beholder. There are always going to be people, also, that say to you, “That's an artefact,” or “That's a bit a mineral. That's not organic.” What we were going to do on Mars was the experiment that is actually an argument that's been put forward for terrestrial rocks, where people see things and they say, “Ooo! These are microfossils. These are organisms that lived 3.8 billion years ago.” and other people go, “No.” The only piece of information that holds out to 4 billion years ago is measuring the abundance of carbon; its isotopic composition, and comparing it to the isotopic composition of a mineral made in water because that gives you an inorganic measurement. If you do these two things and you see these two things are apart (one of the organic matters has got more Carbon-12 in it than the mineral), then that infers that biology has been involved because on earth all biology is actually marked by having more Carbon-12. The biological processes prefer Carbon-12. All biology does that.
