Life From Mars
Friday, September 6, 2013
Could life on Earth have been seeded by Martian life forms hitching a ride on a meteorite? Chemist Steven Benner says that crucial elements for the precursors of organisms on our planet would have only been available on Mars three billion years ago. Benner and planetary scientist Christopher McKay discuss the possibility of the Red Planet kick-starting life on Earth.
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I am Ira Flatow. When we talk about Mars, you know, it's usually about the search for life or water or something like that on the red planet that might be similar to life on earth, right? Is there life on Mars? Was there life on Mars? Was it similar to life on earth? But what if life came from Mars to earth? What if earth was seeded by Martian life forms three billion years ago? It's not a new idea, Martian life forms hitching a ride on a meteorite. But there is a new theory to support it.
Here to discuss it is Steven Banner - excuse me - Steven Benner, distinguished fellow in the Westheimer Institute at the Foundation for Applied Molecular Evolution in Gainesville, Florida. Christopher McKay, a planetary scientist with the Space Science Division at NASA Ames Research Center in Moffett Field, California. Welcome to Science Friday.
STEVEN BENNER: Good afternoon.
FLATOW: Good afternoon. Dr. Benner, last week you had a presentation at - a theory at the Goldschmidt Geochemical Conference that explained why Mars, not Earth, may have been more suitable for the origins of life. You said there were two major paradoxes. Can you explain that?
BENNER: Well, sure. And I think perhaps more interesting than the headline is this example showing how science operates when these big questions are at hand, that is when you cannot apply, you know, the scientific method which you were taught in middle school about clean hypotheses, no value for your observations and so on. I mean, the question, how did life originate is in part a historical question.
Of course we will never have happen to us what happened in the last episode of Star Trek the Next Generation. You remember when Jean-Luc Picard was transported back 4.5 billion years to see the Prebox(ph) who create life. So what chemists do is laboratory work; beakers, lab coats, safety glasses, on how pieces of the first genetic molecule might have originated. So our first problem in the first paradox that you refer to is what we call the tar paradox. it's well validated. You know it perhaps from your own time in your kitchen.
So if you put energy on organic stuff it devolves. It becomes gooey. It caramelizes, it becomes black, and of course if you leave the stove on too long. It certainly does not give life. And so in the laboratory, the first problem is to try to prevent organic material, which we know is on early Earth and early Mars, from devolving. And we show that borax, a mineral containing the element boron prevents this devolution, and especially for carbohydrates.
So it captures this organic stuff before it becomes asphalt, you know, better for paving roads than originating life. Then the next thing we showed in the lab again with safety glasses and lab coats is that minerals containing the element molybdenum, which is in its highest oxidation state, molybdate in this case, for it to work convert the carbohydrates that the borax has rescued from this devolution to tar. And converts them into the correct sugar. The sugar happens to be ribose, which is the R in RNA which of course is a genetic molecule similar to DNA. A little different.
So, you know, we're feeling pretty happy with that. These are interesting results. But then you go talk to the geologists and they'll say, Steve, sorry. Why? Well, because one of the other things we want to do in particular is to dry the system out a little bit because of the so-called water paradox. Lots and lots of parts of the genetic molecules that you have your DNA and RNA fall apart in water. They're hard to make in water. You are here living in water primarily because you have enzymes that repair the damage that water is doing. Those presumably would not have been available to the first forms of life.
So we need a desert, we need borate and we need molybdate. And the geologist said to us, Steve, great chemistry but as far as we can tell the water inventory on early earth was sufficiently high, that the entire planet was flooded, sort of Kevin Costner Waterworld where, you know, a piece of dry soil would be very scarce. So you can't have deserts. They also say, well the borax that we have, boron is not a very abundant element. If it's diluted into a worldwide ocean, you know, you never can get the concentrations that you need to be useful.
And your atmosphere is sufficiently - or insufficiently oxidizing to have much molybdate. And your other guest here actually with Heiman Harvan has actually talked about local environments which have molybdate. But if their diluted into a worldwide ocean, hey, this is a problem. So just as the chemists, you know, with our knuckles dragging in despair leave the room, the geologists say, oh but wait, Mars never has had as much water as earth. Mars never has perhaps - I mean, has always had therefore more of an opportunity to concentrate scarce borax in its surface.
And Mars, you know, you can get all the chemistry you want, Steve. So this is actually an idea proposed by a geologist named Joe Kirschvink at Caltech. And so we discussed it and in front of the geologist, in fact, the guy who had invited me to give this lecture was the person publishing many, many papers saying that we could not have our chemistry on earth. But, you know, there is it, all opportune on Mars.
And so you get into this logic where you first have to decide whether you want RNA or not. And if you don't, you know, there's another way you can go. You can come up with a metabolism for a scenario for the origin of life. Then you've got to decide whether Benner's stupid chemistry, you know, is necessary or not. Well, if it's not, you know...
FLATOW: Well, are you saying that the ingredients for life on Mars are still there, that stuff - or 3 billion and 4 billion years ago Mars had better ingredients to make life than we did or...
BENNER: That's right. We're making a distinction between where life might emerge and what environments might be habitable. That is, where life could continue to exist after it had emerged. So for example, Earth today on the surface has a lot of dioxygen, O2, in the atmosphere. And so the current thinking is that on the surface of Earth is actually hard to get life to emerge new on the surface because it would be oxidized by the oxygen in the air.
Now, that does not mean that Earth is not habitable. It's just not a good environment for life to emerge. So what we're saying is, yes, absolutely. So four billion years ago the argument is almost more of a negative one. So that is that the argument begins by saying that if you think that this chemistry is necessary and if you believe the geologists' model for early Earth, right, then you conclude that early Earth would not be a place where this kind of chemistry could've taken place. Maybe other kind of chemistry could've taken place but not this.
But Mars would have been then - now you've asked another question which is very interesting, is that could Mars also now be a place where you could look for this kind of chemistry? And the answers we don't know well but the answer's almost yes because Mars does not have the oxygen in the air that we have here on Earth. And we have a rover, Curiosity. NASA has a rover down at Gale Crater now. And we're looking at five, five-and-a-half kilometers of sediments which go back in time a long way.
So we ought to be able to find records of the earlier state as well as the ongoing state, which would tell you an answer to that question you asked.
FLATOW: Dr. McKay, would Mars have been more hospitable for life compared to Earth 3 to 4 billion years ago and...
CHRISTOPHER MCKAY: I think Steve's got a good point there. And it's not only true for his particular scenario for life, but a lot of people that have looked at the origin of life and compared Earth and Mars reached the same conclusion that it'd been easier to get it started on Mars.
FLATOW: And how would it have gotten here?
MCKAY: Hitched a ride on a flying rock.
BENNER: Right. So there's (unintelligible)...
FLATOW: You mean like a collision with Mars knocks a rock off of it, because we find meteorites from Mars all the time here.
BENNER: That's right. About a kilogram of Mars comes to earth every day or so. And it gets here a little bit perhaps by volcano ejection, although not so much anymore. But absolutely, meteorites hit Mars all the time. Some of the stuff that's ejected from the surface makes it to escape velocity; a half-life of about nine months on average some of it will find its way to earth. And of course the Allan Hills meteorite which was discussed, oh, 20 years ago from Antarctica is an example of that.
FLATOW: So does it bring the life actually formed as microbes or does it bring the building blocks or does it bring the molybdenum that we don't have here?
BENNER: Right. Well, the model is of course that it brings the life because remember, if the Earth is saturated by a worldwide ocean, any amount of molybdenum or any amount of borax that is brought by a single rock or even a kilogram of rocks is not going to be very useful once it's diluted into the ocean.
On the other hand, you know, if you're sitting on Mars on a Sunday morning, you know, in the sunroom doing a crossword and you get yourself knocked into space, you're going to be frozen. And when you land on Earth and you're going to be put into an area of abundant water. If you - you might regard this as a Garden of Eden because you had been previously scrimping for water on Mars and now you've got a lot of it. You might regard it as an environmental shock of the first order and you might just die.
But the model is that the life originated there, not just the species, the mineral species. And the life came on the rock, shattered from proton storms or happened to come along in the correct nine months of solar activity and landed here with life itself.
FLATOW: Christopher McKay, you're part of NASA's Chem team. You've been zapping the rocks on Mars. Can you find evidence that would back up this theory?
MCKAY: Well, we're certainly looking at the rocks at Gale Crater. We're finding evidence that indeed this was a place where there was water early on. We even reached down into some sediments below the surface which look like they had been deposited by water. They were dark compared to the surface. They were gray and not red. It was very exciting.
It looked like we were really accessing this ancient buried water-like deposit. We searched in them for organic material. Haven't found it yet but there's still a chance as we're analyzing the samples more that we'll find evidence of organics. So we're on our way to doing the sort of thing Steve would like to do. It's very hard when the rover is millions of miles away and we don't have all the tools and laboratory equipment we'd like.
But we're making progress.
FLATOW: And what would it take to show or prove to you that there was once life on Mars like we're postulating here?
MCKAY: The first step is demonstrate there was water. OK. We've done that. We found(ph) the water. We've shown it conclusively. The next step in my mind is to find some organic material. That's what life - water is what life lives in; organic material is what life is made out of. So find some organic material. But we also know that meteorites bring organics to Mars, as they do to Earth.
So just finding organics doesn't mean that they're biological. So the next step after finding that there are organics on Mars is finding evidence that some of those organics are biological in nature. That is, telling the difference between organics made by life and organics made by chemistry.
FLATOW: Mm-hmm. You know, we talk about the Earth being in the exact perfect, the Goldilocks position for - in the solar system for life to have evolved. If this is - if your theory is correct, that life started on Mars and was shot over here by some rocks that landed here, that means you need two planets.
MCKAY: Yeah, that's sort of a worst-case interpretation, is that you need a planet to start things. And then you need a planet to keep it going. And the planets suitable for starting aren't suitable for keeping it going. And the ones that are suitable for keeping it going for a long time aren't suitable for starting it. That's a pretty pessimistic view and it would mean that life is going to be pretty rare in terms of reaching the level of complexity it does on Earth.
But I don't know. We'll only know when we go and dig around Mars a little bit more.
BENNER: Oh, yeah. Chris is exactly right. Let me be a little more optimistic. Keep in mind that one of the consequences of my talk - this is to geologists - is that I'm now getting emails from many of them trying to find - to change the model, right? Finding (unintelligible) in places where we argue that it would not be. Bob Hazen himself is talking about looking at boron in the ancient rock sediment.
At some point the models for the inventory of water on early Earth might change. The models for how early continents would have risen from ocean to give you dry land might change.
BENNER: So the other half of this is, of course, motivating geologists to go reexamine the record, the geological record, with the idea of proving the contrary. That is, finding places where useful chemistry can take place on Earth. But you're right. I mean Mars had a magnetic field at one point. That magnetic field was eventually lost. That, of course, gives the solar wind the opportunity to blow away all of Martian atmosphere, which is a bad thing for life.
And if you're right - if what Chris has just said is correct, that, you know, you need two planets nearby, you know, it would be helpful to maybe have Mars a little larger, but yes, you're right, it diminishes the probability. But not by a lot, I think. And this is why your extra solar planets work is so important.
We actually are just beginning to look out there into the stars and try to make a statement about what the likelihood is of any given star having one, two, three or more rocky planets. The ones that are most interesting to us are the small planets, which of course are the most difficult to detect. But it's going to take a while before we know whether or not two planets nearby as Mars and Earth are is a common event in the solar system or an infrequent one.
FLATOW: This is SCIENCE FRIDAY from NPR. I'm Ira Flatow talking with Steve Benner and Christopher McKay. A couple of minutes left, gentlemen. So where do we go from here with this idea? Are you pursuing it more or is just a topic for a beer?
BENNER: Well, no, we certainly are pursuing it. There is right now on a table a discontinuous synthesis model, as the technical term is. We can, in individual steps, go from carbon dioxide and nitrogen and a little bit of hydrocarbon in what we think might've been the primordial atmosphere all the way to RNA that might be able to catalyze its own replication. That is, from start to finish, a model for the origin of life.
But as the discontinuous word implies in its name, nobody can get it to work all together. What we have is a bunch of individual chemists - John Sutherland, ourselves, lots of people around the world - doing one step at a time in a beaker, isolated. And so our first problem is to try to get that synthesis more continuous with a little bit less hands-on from an intelligent scientist who's sitting there doing the design.
As I've already mentioned, another feature of this is to get geologists to - you know, it's interesting. We go to the poster session, you talk to the students at these meetings, and they are extremely excited to realize that their Ph.D. dissertation, which is, you know, detailing some chemistry of some rock feature from some location is actually a very important part of this larger question of how life emerged.
And so that influences how the geologists look at the record and that's very important...
FLATOW: Yeah. Let me get a quick question from Rose in Redding, California. Hi, Rose. Quickly.
ROSE: Hi. Hi, Ira.
FLATOW: Hi, there.
ROSE: It's so great to be on.
FLATOW: Thank you.
ROSE: Hey, I had a great question. I teach high school biology and we were talking about the development of early life on Earth and we were talking about amino acids and all. And one of my students said, well, there's amino acids now on Earth. Why isn't life developing all around us on Earth? I think I handled it pretty well. Because we talked a little bit about the conditions on early Earth being really different from the way they are now.
But I would love some feedback from your guests on this.
FLATOW: I've got 30 seconds, gentlemen. Who can answer that?
BENNER: I mean my comment is first, how do you know that life is not emerging on early Earth? That's a difficult negative to prove. The classical textbook answer is that above the surface oxygen destroys any nascent life as it is emerging and of course across the planet you already have a biosphere. So if I try to emerge de novo, I'm more primitive than what is already here occupying various ecological niches and I would be eaten. That's the text book answer.
But of course, being whimsical, I always would go back and say, well, what makes you so sure there is no life emerging elsewhere?
FLATOW: Yeah. Oh, well, there you go. We're going to take our safety glasses and lab coats off. Thank you for reminding us about that, Steve. I want to thank you both, gentlemen, for being with us today.
MCKAY: My pleasure.
FLATOW: Have a good weekend. Steve Benner, distinguished fellow in the Westheimer Institute at the Foundation of Applied Molecular Evolution in Gainesville. Christopher McKay, planetary scientist with the Space Science Division at NASA Ames Research Center in Moffett, California. We're going to take a break and when we come back we're going to talk about potential missing link for Alzheimer's Disease. Stay with us. I'm Ira Flatow. This is SCIENCE FRIDAY from NPR. Transcript provided by NPR, Copyright NPR.View this story on npr.org