<<Paul Davies is an astrobiologist at Arizona State University, and in a recent
article in the journal Astrobiology he calls for a mission to planet earth
in search of, what he calls, "weird life
Professor Davies, welcome to Living on Earth.
DAVIES: Thank you.
GELLERMAN: So you’re calling on scientists to search for alien life. In your paper you call it weird life
. What’s weird life
DAVIES: Weird life is life as we don’t know it. All life on Earth that we currently know is the same life, it’s descended from a common ancestor. But, I don’t think we’ve looked carefully enough to see whether there could be another form of life right here on Earth. And what interests me is the issue – has life happened more than once?
GELLERMAN: It’s what you call the shadow biosphere – that is that there would be a second genesis, kind of like a second tree of life.
DAVIES: Exactly right. So Darwin had this idea that life forms a sort of tree, and I think we’re all familiar with that, that species branch and that you can look at all the different species on earth today and trace back when they would have been genetically identical in the far past. And there’s been this assumption for decades that the tree of life is single tree. But I’ve often wondered, could it be a forest. Could there have been many geneses of life either on Earth or somewhere else and come to Earth. And the first thought is, well, surely we would have noticed. But almost all life on Earth that we know, that is that belongs to our tree, is microbial. And you can’t tell by looking at microbes what they’re made of.
GELLERMAN: Yeah, you write that if you had one gram of dirt, there’d be a million microbes and we’ve only characterized one percent of them. So we really don’t – we don’t even know what’s in that gram.
DAVIES: Exactly right, yeah. We tend to notice the big things, the elephants and the oak trees and, of course, the people, but overwhelmingly, life on Earth is bacterial life or there’s another branch of microbes called Archaea. And they make up the lion share of all life. But most of these haven’t been characterized or catalogued and nobody really knows what’s out there. And I’m just saying let’s be open to the fact that there could be microbes from a different genesis of life from you and me.
GELLERMAN: Well all this really begs the question, what is life? What is life?
DAVIES: Well, you probably remember in high school all these definitions like reproduction and metabolism and response to stimulus and so on. Now the difficulty is that for every one of those properties, you can find something that we all agree is not living that shares them. So for, example, crystals and bush fires replicate. And then the flip side is we can find living things that don’t satisfy some of those definitions. So mules, for example, are certainly living, but they’re sterile, so they don’t reproduce. But some people turn the whole thing around and they say that any system that undergoes Darwinian evolution is by definition living. It doesn’t really matter too much for my purposes except the transition from nonliving to living should be a well defined thing. And the difficulty is that even the simplest known living cell is already so immensely complex it’s inconceivable it just sort of popped into existence ready made. It would have had to have come from some long series of simpler, earlier things. And we don’t know what those things are. And one of the fascinating aspects of this entire study is that if we go look, if we go out there to look for another form of life, weird life, we might find that, of course, but we might also find a living fossil, a precursor of familiar life.
GELLERMAN: Well here we are living on Earth, where would you boldly go where no one has boldly gone before to find weird, unknown life?
DAVIES: Well, there are two strategies here. One of these is that we could look somewhere that’s beyond the reach of known life because then it’s easier to identify. If anything’s living there and we know that known life can’t, well, then, by definition that’s going to be weird life. So my first thought is to look in areas that are just simply so hostile to known life that maybe weird life has got a toehold there. But the other scenario, which is actually I think more plausible is that weird life and known life are simply intermingled. That is that these weird or alien bugs are all around us because you can’t tell by looking what they are. And if you go and see microbiologists at work and ask them do they ever have any microbes they’re working with they’re having difficulty with, they can’t culture them, they can’t sequence them – well all the time. And what happens to these, well, they get thrown down the sink. So, it’s entirely likely that microbiologists have seen weird life but not recognized it for what it is because its not going to stand out saying “I am weird.” It’s not going to be wearing a uniform.
GELLERMAN: So how would you know something when you didn’t know what you were looking for?
DAVIES: That’s part of the difficulty. So you need to make an educated guess as to how weird life might differ. And so, all life uses molecules that have the same handedness. That is that DNA is always wound like a right-handed spiral staircase, a right-handed helix. And amino acids that make up the proteins in our bodies are all by some definition left handed. Now there’s nothing in the laws of chemistry that says something’s got to be left handed or right handed, but life has made one particular choice. But we can imagine that life would use all the same stuff, the same bases for DNA, the same amino acids for proteins, identical molecules, but the mirror images, called this mirror life, if you like. And then one way of identifying that is you make a soup, a nutrient medium of mirror molecules and you see if anything will grow in it.
GELLERMAN: You know that soup, I think I have some of that in my refrigerator from a few years ago, way in the back.
GELLERMAN: If we did find alien life on Earth, what do you think we might learn?
DAVIES: Oh I think this would be the most stupendous discovery in biology since Darwin, because it’s telling us what we would really like to know which is that life is not a stupendously improbable freak. It’s not just an accident of chemistry that’s occurred only once in the universe. It’s something that emerges naturally and relatively easily from the underlying laws of physics and chemistry. Now, the truth of the matter is that we don’t know. It could be that that’s it – we’re alone in the universe. Or it could be that it does emerge more or less automatically and readily in Earth like conditions and there’s no planet more Earth like than Earth itself. So, if it’s true that life pops up on Earth like planets around the universe, it should pop up many times here on Earth. So we would test that and if we found that yes, indeed there isn’t just one form of life on Earth, there’s two or maybe ten – who knows – we could say with confidence that we will find life all around the universe and with almost equal confidence that we are not alone. And that is a very very deep and profound conclusion. And we can do it without basically leaving our own planetary doorstep.
GELLERMAN: So Professor, why do you think the search for different life forms is so interesting to us earthlings?
DAVIES: I think we are curious because it touches on some of the deep issues. Go back 500 years when everybody’s thinking about the nature of life was based on religion. And so in Europe at that time, Giordano Bruno, while he lived somewhat earlier than that, was burned at the stake for, in part, suggesting that there are other inhabited worlds. Because the idea was that human beings and life on Earth was God’s special creation. And then after Darwinism, people accepted that this wasn’t so, that life is a natural phenomenon, that we have emerged from nature naturally. And then the question is, you know, are we freaks? Is this just an accident? And some people don’t like to think of themselves as freaks. They feel more comfortable with the idea of a biofriendly universe that brings forth life as part of its grand overarching scheme. So, I think the answer to this does touch on some very, very deep issues about what we think of ourselves and how we position ourselves in nature. It does matter.