How The Origin Of Life On Earth Can Help Find Life In Space

IRA FLATOW: This is Science Friday. I’m Ira Flatow. One of the biggest questions of our time, or almost any time, is about life elsewhere besides Earth. Does it exist? If so, where is it, and how do we find it? And if there is life somewhere, does that mean Earth really is as exceptional as we’ve grown to believe?

That question is at the center of a new book written by my guest. Mario Livio is co-author with Jack Szostak of Is Earth Exceptional? The Quest for Cosmic Life. Dr. Livio is an astrophysicist previously with the Space Telescope Science Institute, which operates the Hubble Space Telescope. And he joins me from Hoboken, New Jersey. Welcome back to the program.

MARIO LIVIO: Thank you very much for having me.

IRA FLATOW: You’re welcome. All right. What do you mean by asking, is Earth exceptional?

MARIO LIVIO: Well, the question is really we haven’t found, so far, life anywhere else other than Earth. And it’s not for lack of trying to find. So the question is, is life extremely rare and perhaps complex life or intelligent life even more rare? In which case, it would make the Earth exceptional, which is an idea that we don’t like to jump into, but it definitely is worth thinking about.

IRA FLATOW: Yeah. Is this still as big a question as it has always been?

MARIO LIVIO: Some things have really changed in the past three decades or so in that we now know that there are planets that are– many of them are Earth-sized around other stars. And not only that there are planets around other stars, but planets also in what we call the “habitable zone,” which is that sort of Goldilocks zone, which is neither too hot nor too cold to allow for liquid water on the surface of a rocky planet. So that much we know.

For example, our Milky Way galaxy– there are probably– there may be even as many as a billion such planets. So we know that in that sense, we are not exceptional. But we have still not found life anywhere else other than life on Earth.

IRA FLATOW: Is that surprising to you that we haven’t so far?

MARIO LIVIO: Yes and no, I would say. Now that we know more about the origin of life on Earth, we realize that many things had to happen simultaneously at the same place in the right order and so on to actually– for life to emerge. And we don’t know how to calculate the probability of that.

So in some sense, even if I told you that there are a billion Earth-like planets in the Milky Way, I cannot tell you that the probability for life to emerge, even if the conditions are right are better than one in a billion. So this is why I’m perhaps not as surprised as I might have been before we understood many things on the origin of life.

IRA FLATOW: Yeah, but if you multiply that billion planets in the Milky Way by a billion other Milky Ways in the universe– and I’m thinking of the old Drake equation now, right?

MARIO LIVIO: Yes.

IRA FLATOW: Then the odds have to be that there’s life somewhere else. Doesn’t that make sense?

MARIO LIVIO: [LAUGHS] Again, if you asked me this before I knew anything about the origin of life on Earth, I would have said absolutely, and not just by a billion. There may be as many as 2 trillion galaxies in the observable universe. So the numbers get really big.

But because we have no idea, honestly, at this point, no idea what is the probability for life to emerge and certainly for life to reach a complexity that allows intelligence to emerge, maybe the probability is even lower than that. It’s not something I like. But I cannot tell you that it absolutely cannot be.

IRA FLATOW: Right. And let’s talk more about life here on Earth, because if we’re going to look for life on Earth, we have to figure out how it might have started here, right?

MARIO LIVIO: Right.

IRA FLATOW: So what do we think now about life starting here on Earth? I followed this in my career over the years. And there have been all kinds of chemical evolution theories and things like that. Where are we now with where we think life started, how it started?

MARIO LIVIO: So really, biochemists have made incredible progress in the past 20 years or so. And the idea is the following. You see, what used to be a great obstacle for many years is that modern life, life of today, everything depends on everything else in a circular way.

For example, you need DNA in order to do the proteins. But in order to make DNA, you need the proteins, enzyme proteins to make DNA. So this was a chicken-or-egg type problem that was extremely difficult.

But then it was discovered that RNA actually can act also as an enzyme. This was discovered in the 1980s. And once you discover that, you say, whoa. Then RNA can serve as the chicken and the egg. It can both store information and transmit information and can, at the same time, also act as a protein enzyme.

And this led to this idea of what we call the RNA world that maybe all of life on Earth started simply with RNA. Once you reach that, you say, OK, so the idea is how was RNA formed on the early Earth? And there, great progress has been made.

IRA FLATOW: Well, give me an idea about that.

MARIO LIVIO: OK. So RNA, it has a backbone that is made of phosphates and sugars. And it has four nucleobases, which, for short, are called A and G and U. Biochemists now have found ways in which two out of the four nucleobases can be formed.

There is a very plausible way of them to have formed on the early Earth under the conditions that existed on the early Earth. So that’s only two out of four. But that’s a long way forward.

Plus proteins are made of amino acids. These are the building blocks of proteins. They found that the same chemistry that makes the two nucleobases can make 12 out of the 20 amino acids that all life depends on. So there is a long way– there is still a long way to go, but there is enormous progress.

IRA FLATOW: And where would they come from? Would they be found on Earth? Or would these building blocks be brought in by all these meteorites over the eons hitting Earth in its primordial state?

MARIO LIVIO: So there is no question that meteorites, asteroids, and so on can bring some amino acids with them and so on. But what researchers are trying to do in the lab, to actually build them from materials or compounds that are known to have existed on Earth at the conditions that existed on Earth. And that’s how they actually succeeded to do what I just told you.

IRA FLATOW: Right. Do you think we are close to discovering life in other places in outer space?

MARIO LIVIO: If you asked me 10 years ago, I would have said that maybe we are a decade away. Well, you ask me now. I say we are about a decade to two decades away. But we certainly are getting there.

I mean, look, we found all these extrasolar planets, which are kind of similar to Earth. And they are in the habitable zone, which allows for liquid water on their surface. And we have ways now to try to characterize the atmospheres of these exoplanets, namely to say what is the composition of these atmospheres.

Especially with the James Webb Space telescope, we’re starting to be able to– started a little bit with Hubble, but now with the James Webb, we’re doing this even better. And with the next generation of Space Telescope– in particular, there is one planned, the Habitable Worlds telescope– we hope to be able to characterize the atmospheres of two, three dozen such planets.

And then we can start telling because what life does is it takes such atmospheres out of thermochemical equilibrium. It’s a bit like you cannot have a bunch of graduate students and lots of pizza in equilibrium in a room. One consumes the other.

And similarly, if you find an exoplanet that has an atmosphere that’s rich in both oxygen and methane, let’s say, that cannot be in equilibrium. I mean, that is driven by life. And that’s what happened on Earth itself.

So if we manage to find that, that would be a very strong biosignature. I mean, it will say that that planet is very likely to harbor some form of life. Now, I’m not saying there are crocodiles there or things like that, but simple life forms, yes, bacterial life of some sort and so on.

IRA FLATOW: So we’re looking for, basically, the pizza crusts that are left over from what’s going on– what’s going on over there. What about our own galaxy and our own solar system, even closer to home? Where do you think is the most promising place to look for life here among our own planets?

MARIO LIVIO: Yeah. So first of all, we have to think about the rocky planets. And those– well, Mercury is way too hot. Earth we know there is life. So this leaves Mars and Venus. So the one that is most looked at is Mars, because Mars formed, basically, from the same type of compounds that Earth formed from.

And plus, we know for a fact that some 4 billion years ago there was liquid water on the surface of Mars. It lost it because it lost also its atmosphere and it lost heat. But for example, some of the landers, the NASA landers, tell us that there probably is lots of liquid water some 6 to 10 miles deep inside Mars.

So I would say we definitely have to look for signs of past life. I mean, probably no life today, but past life on Mars. I will be, in fact, amazed if absolutely no sign of past life is found on Mars.

Venus, we thought that it wasn’t such a good candidate. But again, two, three years ago it was discovered that maybe in the upper atmosphere of Venus, there is this thing called phosphine, which is from phosphorous and hydrogen. And on Earth, that compound is made by bacteria.

So there are some missions planned to Venus to also tell whether there is anything there. And the story doesn’t end there.

We discovered that in some of the moons of the giant planets, Jupiter and Saturn– so, for example, Europa is a moon of Jupiter. Underneath a thick ice, there is a liquid ocean underneath. And similarly, this thing exists in moons around Saturn like Enceladus and Titan.

And so there are missions planned. In fact, a mission to Europa is just now taking off to study these moons to see if there is any possibility for life there.

IRA FLATOW: I guess Arthur C. Clarke got it right to go look at those places.

MARIO LIVIO: Yeah. Well, Philip Morrison, who was a famous physicist, he basically said that, we don’t know the chances of finding anything, but we know that if we will not search, the chances are zero. So we have to search.

IRA FLATOW: We talk about looking for life. Are we, do you think, psychologically, emotionally ready for the discovery of life someplace else?

MARIO LIVIO: Well, the real answer is that I don’t know. But I want to point out to you that there was a point where an announcement was made that life may have been found in a meteorite that came from Mars. It was known as ALH 84001.

IRA FLATOW: Had those little nodules on it, right?

MARIO LIVIO: Right. Right. And well, that turned out not to be correct. But nevertheless, when the announcement was made, sure, I mean, the scientific community was very interested and so on. But it didn’t really completely shake the general population.

Now, maybe it was because, if at all, if there were to be true, they were just some form of bacteria and nothing more interesting than that. Maybe if we were to find a complex or intelligent life somewhere, it would have more of an effect.

But I heard once the director of the Vatican Observatory say that if religion survived things like Copernicus and Darwin and so on, probably religions will survive even the detection of extraterrestrial life.

IRA FLATOW: So they’re getting ready to deal with it, it sounds like.

MARIO LIVIO: I think so, yes. Or they think that maybe the effect would not be so large, so they even don’t have to deal with it.

IRA FLATOW: What do you think about people who are fearful that– not that we would find life out there, but like in the science fiction movies, aliens would find life on Earth.

MARIO LIVIO: Yeah. I’m not fearful about this because, look, my feeling is the following. If there are extraterrestrial civilizations out there, intelligent civilizations, it is much more likely that they are more advanced than us by maybe a billion years than the other way around.

If they are more advanced than us by a billion years, they probably found us already. And they are just not interested in the same way that– are we trying to communicate with the worms of our world? We are like worms to them. So I think that I don’t fear that really too much.

IRA FLATOW: Well, I’m with you on hoping that we do find something or something finds us.

MARIO LIVIO: I hope so, too. And I also hope that it will happen during my lifetime.

IRA FLATOW: I’ll second that motion. Dr. Livio, Mario, thank you for taking time to be with us today. It’s an excellent book. I hope a lot of people get to read it.

MARIO LIVIO: My pleasure. Thank you very much for having me.

IRA FLATOW: Mario Livio, who is co-author with Jack Szostak of Is Earth Exceptional? The Quest for Cosmic Life. Dr. Livio is an astrophysicist previously with the Space Telescope Science Institute, which operates the Hubble Space Telescope.

And he joined me from Hoboken, New Jersey. And you can read an excerpt from the book. Yeah, you can head to our website. Go to sciencefriday.com/cosmiclife. Sciencefriday.com/cosmiclife.

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