|If life does occur outside of earth, is it limited to single-celled microbial life such as bacteria? |
Neil deGrasse Tyson is the Director of the Hayden Planetarium at the American Museum of Natural History in New York, and also a Visiting Research Scientist at Princeton University’s Department of Astrophysics. He writes a monthly column called "Universe" for Natural History magazine, and is the author of several books, including "One Universe: At Home in the Cosmos" and "The Sky is Not the Limit: Adventures in an Urban Environment".
|"Life might have originated in Europa early in the solar system’s history (and may live there still." -Peter Ward|
Astrobiology Magazine (AM): One interesting point you make in the Origins companion book is that while we are just a tiny part of the galaxy, UFO and alien stories imply we are the center of attention in the universe. You also note that, because of the vast interstellar distances between possible civilizations, contact may never be possible. If that’s true, then how would our "self-centered" viewpoint be harmful? Just how bad is it that we’re so self-centered?
Neil deGrasse Tyson (NT): I think our big human ego can blind us from making or accepting certain kinds of scientific discoveries. It’s why it was hard to accept the decentralization of our position in the cosmos: that the Earth revolves around the sun and not vice versa. There’s no reason why this information should be hard to accept unless you have an ego or dogma that’s fighting it.
But I think a consequence of greater impact is in view around the world today. So much of the world’s problems come about because some people see themselves as more important than others. The simple notion – "I’m more important than you" – can lead to devastating political social consequences, like war and other forms of bloodshed like civil unrest. An attitude of self-importance can show up politically, culturally, religiously, spiritually, or in whatever way people divide themselves. They choose up sides, one side thinks they’re better than the other, and go to war over it.
I don’t know if I’m just a hopeless dreamer, but I’d like to believe that the cosmic perspective, which is brought about by any kind of study of our smallness in the universe, makes you vastly more humble as a citizen of the planet. And from my reading, it makes you less likely to take up arms against one another, or to invade another nation. The world might just be compelled to live in greater peace when we’re made aware of our statistical, temporal, and spatial insignificance in the cosmos.
|When the book "Rare Earth" was first published several years ago, it raised a great deal of controversy among astrobiologists. Written by Peter Ward and Donald Brownlee, the book’s hypothesis suggests that complex life is rare in the universe, and may even be unique to Earth.|
Credit: SETI League
AM: Moving aside from the politics of it, do you think an Earth-centered viewpoint could affect the direction of science? For instance, I know a lot of people criticized Peter Ward’s book Rare Earth for being too Earth-centered in its thinking. Such a viewpoint may then limit our search for life by causing us to only look for planets that are Earth-like.
NT: Yes, that’s a good example. You end up writing books like Rare Earth when you’ve convinced yourself of the idea that we are something special. There’s another book called Privileged Planet, but that one has a clearer religious agenda.
AM: In "Origins" you mention the four elements necessary for life to appear anywhere: a source of energy, a type of atom that can build complex structures (in our case, carbon), a liquid solvent (in our case, water), and enough time for life to appear and evolve. Since this describes elements necessary for "life as we know it," do you think this list commits the crime of being too Earth-centered in our thinking?
NT: No. There’s nothing wrong with that approach in the search for life "as we know it." Rare Earth, on the other hand, is saying, "we are the only life as we know it," which is a very different perspective.
AM: Don’t you think some would say that we’re just limiting ourselves by looking for life as we know it?
NT: Life probably exists in more ways then we can think of. Of all those other ways, in an environment of limited funds, you want to start with what you know has already worked — you start with life as we know it. Then, if you’re successful or not, you build up evidence for either finding it or not finding it. You say, "Ok, we were unsuccessful this way, or we were successful this way, now let’s see what other variations we can find." It’s just how to be efficient in this or any scientific investigation of the unknown.
But you’re right, it could be limiting. We’re looking for Earth-like planets around sun-like stars, because we know there is life around at least one Earth-like planet around at least one sun-like star. You can’t fault us for using ourselves as a template. But like I said that’s very different from saying we’re alone in the universe.
AM: My reading of Rare Earth was not that we’re alone, but that you need all these things on Earth that makes complex life possible, like tectonics, oxygen, liquid water, iron – all these conditions need to come together. There are so many necessary conditions, in fact, that while they could all occur somewhere else in the universe, the likelihood of that happening is very low.
|"In places like Io (left) and Titan (right), we may find the first evidence of other biochemistries that are beyond our powers of prediction." -Frank Drake|
NT: The arguments in Rare Earth are indeed compelling, and I’m not even disagreeing with most of them. But throughout the history of writings on this subject, if you read anyone’s account of the rarity of life or even human life, they all sounded compelling. Read Ptolemy. He said the sun, the other planets, and the stars all go around the Earth. But that’s wrong; we’re going around the sun, not vice-versa, and that fact undermines the entire foundation of the argument, even though it read really well at the time.
Every time we think something is rare we find it to be common. For example, there’s the idea of a habitable zone around a host star. If you read the early accounts of this, people would remark, "The planet’s got to be just right!" Then you learn there’s a greenhouse effect, and you can have various levels of greenhouse effect and surface reflectivity, which can make your planet either colder or warmer than what the native temperature would be if it just sat there, bare, at a given distance from the host star. All of a sudden, your habitable zone is considerably broader than you had originally imagined it to be.
Then you read our early biology textbooks that said, "Life requires sunlight to survive." But no, life simply requires energy. Out there on Europa we have an energy source traceable in part to the tidal forces of Jupiter, rendering liquid what would otherwise be completely frozen. So that net you use to search for life has grown. And then you learn about the whole branch of life called extremophiles, and how hardy life actually is. Bacteria and other creatures living in the extremes of temperature, pressure, radiation and liking it. So once again, your definitions are broader, not narrower, than what you had originally imagined, because nature is cleverer than we are. In other words, just because you haven’t figured it out doesn’t mean nature hasn’t figured it out. That is the history of these lines of reasoning.
So I see Rare Earth-type books as the next attempts to try and make us all feel special. If you want life exactly as you have it here on Earth, then it seems like you’d have to produce all those series of events. But we haven’t done the experiment where you change some of those variables. What happens if carbon isn’t subducted down into the limestone with plate tectonics? Will life find some other way to survive and thrive that we haven’t yet even thought of?
Biologists, who revel in the diversity of life on Earth, at the end of the day confess to themselves that life on Earth has hardly any diversity at all. We all have some amount of common DNA. If you want diversity, then find a life form that started on another planet. Life with no DNA in common, or perhaps more likely, no DNA at all. Then you’re talking "biodiversity." That would imply that life doesn’t need this long string of specific complicated events. Then we can have a whole new kind of conversation.
AM: So when you cite these four things life needs, you see those as the bare bones…
NT: Bare bones! That’s exactly it. You boil it down and say, "I don’t know or care about the tectonics, or the green zone, or this or that, just give these fundamental ingredients, and let the chemistry take care of the rest.
AM: David Grinspoon said to me in an interview once that a planet and its life forms co-evolve.
NT: Yes! Perfect way to say it! Whereas here you are looking at us, and you look at the string of events, and you say, "Gosh, that’ll never happen ever again for the rest of all of the cosmos." Well, calm down, take a deep breath, and look at what you haven’t thought of.
So it’s restricted creative thinking that allows people to ride their ego longer than they ought to, and deeper than they ought to. It’s the absence of creative thinking that centralizes us.
And by the way, I don’t have any idea what life would look like if it didn’t have these "special conditions," but carbon chemistry is remarkably fertile. Given the behavior of carbon in the universe, I’m pretty sure life elsewhere will have carbon chemistry. As we remind the reader in our Origins book, carbon can form more kinds of molecules that all other kinds of molecules combined. So there are things we can bet on, like the four conditions I outlined. As for the rest, I’m not impressed.
Related Web Pages
A Perfect World I: Tyson
The Origin of Life on Earth: Book excerpt
The Search for Ourselves in the Cosmos: Book excerpt
Tyson and Planetary Society
Tyson Testimony to Congress on Astrobiology
The Bigger Picture
What Would a Martian Drive?
Three Tough Questions