How Rare Is the Earth?

What are the chances that there are many other planets in the universe as hospitable to intelligent life as ours? Peter Ward, a paleontologist at the University of Washington and coauthor (with Don Brownlee) of Rare Earth: Why Complex Life is Uncommon in the Universe, argues that while simple life-forms like extremophiles can exist in harsh conditions, complex life requires much more benign and stable conditions. As a result, Ward believes that we are effectively alone in the universe.

ALONE OR JUST LONELY?

NOVA: What first got you thinking about the possible existence of alien intelligence?

Peter Ward: Well, who isn't, actually? I mean, what person really isn't thinking at least about ourselves and our aloneness or not? We are so immersed in aliens, you can't get away from it. I would say that the top four of the 10 greatest box office hits of all time were dealing with alien life in some way or another. And somewhere along the line you have to start asking yourself, well, what are the chances?

Don Brownlee and I started [working on the book] Rare Earth sitting together at a lunch table. We knew each other, but barely. I think the conversation started where I was saying, "Well, you know, I'm just sick and tired of all the damn alien shows. [Finding aliens is] hardly likely at all." And he said, "Really? I think the same thing." And off it went.

In Rare Earth you talk about how we're very lonely in the universe. But lonely doesn't mean alone. Do you think there probably is alien intelligence somewhere?

Yeah. I think there absolutely has to be. The numbers are just so great. In the first two billion years of the universe, you certainly didn't have life, because you just had hydrogen and helium. That's a pretty boring universe. But once we started building elements, you could have a little more complex chemistry going on, organic chemistry, and then off it went. But we're far enough along in this whole universe, it's highly probable. I would say it's so probable that I don't see how you could bet against it.

Carl Sagan hit the nail on the head—"Billions and billions," right? People made fun of him for that. But the reality is, he was quite right. The numbers are so staggering: billions and billions of galaxies, with billions and billions of stars. This was becoming close to the infinite number of monkeys and typewriters.

"If there's no higher plant life, there's not going to be higher animal life."

You've said in your book that for all intents and purposes, we're alone. But can you imagine a finding that would really change the odds of finding alien intelligence?

There is a very simple way, I think, to look for alien intelligence. It requires the ability to image Earth-like planets. We'll be there soon. Once you can image an Earth-like planet, all you need to do is start looking in the spectrum for a really strong signal from mercury.

From mercury?

Yeah. If you think about it, how do we make streetlights? They're all called mercury vapor lights. The strongest streetlights in the world are made from one or two elements that actually give off a very strong signal. Any engineer is going to settle on the same way of making a light. There's not going to be some supernatural light out there.

You can pick up the spectral signal from our world from a long way away. You've seen the pictures of the night side of the planet covered with lights. That's going to send a very strong signal out there.

There's another simple way to figure out if a planet is even worth looking at. And that is, what type of rivers does it have? Dave Montgomery and I published a paper in Science in 2000. We pointed out that, prior to the Devonian Period, there were no meandering rivers on Earth. There was no Mississippi meandering across the floodplain. All rivers were braided, because you can't have the normal rivers you find on Earth today without plants for banks to be built.

This is pretty clear-cut in Washington State—trees go away, the rivers change from meandering to braided streams. So just start imaging the rivers on a planet, and you'll know if there's higher plant life or not. If there's no higher plant life, there's not going to be higher animal life.

THE MEDEA HYPOTHESIS

Your book The Medea Hypothesis, which proposes that life is inherently suicidal, suggests that complex life doesn't last long. If true, what impact does this have on the possibility of finding alien intelligence?

Well, that's certainly what Don Brownlee thinks is the most important part of the Drake equation. [The Drake Equation is used to estimate the number of detectable extraterrestrial civilizations in the Milky Way.] How long do complex civilizations stay complex? We're going to come to that test here pretty quickly in the next century or the next millennium. If we continue to increase carbon dioxide, producing what I think will be a runaway sea-level rise, then we're going to put this to the test. When you have too many people and no food and civilization falls into chaos, how much civilization is retained? How long will an intelligent species survive?

"Intelligence is the only way that you can stop this whole process of life killing off life on the planet."

Can you tell us more about the Medea hypothesis and how that figures into the lifetime of an advanced civilization?

The only reason Medea came to my mind is that she was chasing a very wayward life. [Editor's note: Medea is a figure in Greek mythology who kills her own children by accident.] The fact that life seems to screw everything up for itself over and over and over really negates the sort of wonderful thought that Mother Earth is going to bail us out over and over. Mother Earth doesn't bail us out. Life is a very complex phenomenon that's very selfish, and it leads to population disasters over and over.

I argue that the only way out is intelligence. Intelligence is the only way that you can stop this whole process of life killing off life on the planet. Inevitably it's going to happen here. Carbon dioxide is going to drop to the point that the planet can no longer produce plant life. And then, 20 million years after that, the oxygen is gone and there go the animals. So without us radically changing things really quickly, the Earth becomes uninhabitable for complex life in a half a billion to a billion years. That's all Medean.

What do you think about the idea that in another couple hundred years it won't be biological life, it'll be synthetic life?

Oh, I think it's coming. And interestingly, I just did a whole day shoot for Morgan Freeman on the Through the Wormhole series just on that particular question. For some reason, I seem to be pigeonholed with the future evolution of humans. I wrote a paper about that in Scientific American, and all of a sudden that's me. There are a lot of people who know a hell of a lot more about it than I do. But I really do think that we're going to find this synthesis of the machines and us.

THE RARE EARTH EQUATION

In your version of the Drake Equation, which you called the Rare Earth Equation, you replaced the factor "communicating civilizations" with "complex metazoans." Why complex metazoans and not communicating civilizations, or intelligent life?

Well, we just wanted to up the ante. Every argument has always been what is the percentage of planets that have complex intelligent, communicating species? And we started out thinking about this, but we wanted to separate it in our book. So we made it even simpler. What is the percentage of planets with worms?

You know, there is going to be some fraction of the planet with worms, where the worms finally evolve into human being-like equivalents. But the odds against even getting worms, it occurred to us, was so high that this would make our argument even stronger, which it did—the fact that animals were tough to get to. And why is that? Well, to have animals, you absolutely have to have oxygen. But it took more than two billion years to get there.

"How can you get to be a complex civilization without metal and electricity?"

It doesn't seem like there have been many people who've gone out on a limb and assigned a value to the Drake Equation, or to the Rare Earth Equation. Have you?

No. We always stayed away from that. Every once in a while, every two or three years, we get a paper where somebody goes out on a limb and tries it. We were never interested in trying to come up with an absolute number. All we wanted to do was point out the conditions and the problems to get there.

It's even starker than that. Let's say you had a water world. Would those creatures ever communicate? How in the world would you ever smelt metal underwater? How in the world could you ever produce electronics underwater? I mean, we know what happens when you put water on electronics—it shorts out because the electrons go everywhere.

How can you get to be a complex civilization without metal and electricity? Maybe you could have these creatures in the opposite of a scuba suit, where they're in water, right? They've got these little water lumps walking around on the land, and they produce telescopes. But underwater creatures are probably not going to have any sense of what the cosmos is, or care.

THE EVOLUTION OF INTELLIGENCE

Do you think the evolution of complexity is the natural order of things? Is that always going to happen? Is intelligence always going to evolve?

On the first question, complexity is already going to happen if you get an advantage being complex. The advantage that takes place is locomotion and movement. You cannot move rapidly or move at all, really, unless you have multi-cellularity. And once you have that, to be able to move well you need muscles. You need some sort of skeleton to thrust against.

So if any aspect of speed is better at finding food, which it is, or escaping predators, which it often is, then that's going to evolve. But intelligence, on the other hand—why weren't there intelligent dinosaurs? Or why didn't intelligence come in the mammal-like reptiles? Or why did it take the entire Cenozoic Era to get the primates with big brains?

Intelligence has a very high negative aspect to it. Maintaining a big brain is a real problem for organisms. Nervous systems and that much mass require so much oxygen that it's really a burden to the animal. You only get as intelligent as you have to be. And for finding food, the big cats, the big dogs, for 30 million years, they've been very good at it. And there's been no reason for them to get better at it.

There were special circumstances and accidents that created a world in which hominids could actually be pushed into high intelligence. And the fact that it did not happen prior to this is just that there aren't many body plans or many evolutionary scenarios where you need to have brains our size.

"That's why I laugh when I see all these science fiction stories about how we'll get even bigger heads. You know, no one talked to the women about that!"

Is there a downside to being intelligent aside from the cost of the food?

There's certainly a downside for childbearing because obviously humans have an enormously high death rate in childbearing. Head size and the female human pelvis were on a collision course. And we really were walking a very thin knife-edge here. So many babies died in pre-civilization childbirth that you had this strong evolutionary pressure to reduce head size so you could have a greater longevity and a greater number of females surviving. That's why I laugh when I see all these science fiction stories about how we'll get even bigger heads. You know, no one talked to the women about that!

Some people find the suggestion that we're very lonely arrogant because it seems like yet another example of humans believing we're special.

We are special. I mean, we're certainly special in the solar system. We're certainly special on Earth. You know, why not be special and enjoy it? And why have a guilt feeling about it?

There is also the argument that it's arrogant to think that intelligence like ours is pre-ordained. Are these kinds of discussions what happens when there aren't enough data?

Oh yeah. And this is a case where there certainly aren't enough data. But the really interesting thing that's been happening is still the exoplanet searches. That's the greatest breakthrough in any of this discussion in the last decade. Because even 10 years ago we really thought that maybe planets were only present around 15 percent of stars.

In fact, the recent discovery of a planet orbiting a multiple-star system, that really increases the odds. So yeah, there could be tons of planets out there. The trouble is, we haven't found one Earth-like planet yet.

SETI

Do you think SETI, the Search for Extraterrestrial Intelligence, is a futile search?

No. I used to think so; it's such a long shot. Personally, I don't think they'll ever find a signal anywhere. But as long as there are people willing to fund it, and it doesn't cost the public anything, why not? You've got really, really interesting people working away at it.

I had to laugh at that movie Contact, where Jodie Foster plays this brilliant astronomer coming out of grad school who goes right into SETI and gives up her position at Harvard. There's no reality to that. Ph.D. astronomers now, they're not going into SETI. The people who go into SETI are late-career people who've got nothing else to lose.

Britain's Science Council recently spent a year working on a new definition of science, which says that "Science is the pursuit of knowledge and understanding of the natural and social world, following a systematic methodology based on evidence." What do you think of that definition? And how do you think the search for alien intelligence fits into that?

Well, I teach 250 people starting tomorrow, and my first lecture is always, "What is science?" What I like to tell them is that science is a verb, not a noun. They kind of look at me like, "What?" It isn't just accumulated knowledge. It's the acquisition and then using that knowledge. You never stand pat, because that isn't science. That's just an encyclopedia.

"We don't go to lunch and talk about, 'Well, what do you think about the chances for intelligence today?'"

What about SETI? Is it predictive?

The way SETI is predictive is that it takes into account the findings from astronomy, exoplanets, planetology, all that stuff. SETI has to take into account all that knowledge so that they can target. They don't want to target everything. They want to go for the stars with the highest probability. Well, how do they know which ones those are? That comes from all the various disciplines and a whole giant knowledge set.

We don't yet know enough about the conditions necessary to keep complex life alive for a long time. We're still working on that, and that will help SETI. And there's no reason that SETI has to die out in the next 50 years. We're in this for the long haul. We humans are going to be here for a long time. Maybe SETI, a thousand years from now, has so refined the search that they've increased their instrumentation that they finally do find something way out there.

At the end of the day it seems like the question of the existence of extraterrestrial intelligence is not if but how many. Do you agree?

Every reasonable person I've talked with, once they know the numbers, give it a probability. It's never yes or no. It's just "the chances are." That's about as far as it goes. People don't talk about it that much. And we don't go to lunch and talk about, "Well, what do you think about the chances for intelligence today?" It just doesn't come up, because it's non-retrievable from a scientific point of view right now. Other than SETI, it doesn't seem worth anybody's while. There are other things to worry about, like funding.