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Season 4, Episode 14: Gardens at the Bottom of the Sea

Season 4Episode 14Aug 7, 2020

Laurie Barge, an astrobiologist at NASA’s Jet Propulsion Laboratory, studies how plant-looking mineral structures called chimneys grow from chemicals found at the deepest depths of the ocean. In her lab she has glass vials and bulbs full of different chemical mixtures that simulate undersea conditions.

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Laurie Barge, left, and Erika Flores, righ

Billions of years ago, life may have gotten started at hydrothermal vents, cracks in the sea floor where hot fluids from inside our planet mix with colder ocean water. Laurie Barge, an astrobiologist at NASA’s Jet Propulsion Laboratory, studies how plant-looking mineral structures called chimneys grow from chemicals found at the deepest depths of the ocean. In her lab she has glass vials and bulbs full of different chemical mixtures that simulate undersea conditions. Through careful mixing, scientists can even form amino acids, which are essential building blocks of life. Could similar processes happen in oceans under the ice shells of moons farther away in our solar system, like Europa and Enceladus?

Jim Green: How could we possibly find life beyond Earth if we don’t even know how it started here?

Laurie Barge: We don’t actually know where the first life lived. There’s theories that it could have been on land, underwater in a vent at a high temperature.

Laurie Barge: We really don’t know what exists beyond the last ancestor.

Jim Green: Hi, I’m Jim Green, chief scientist at NASA, and this is “Gravity Assist.” On this season of “Gravity Assist” we’re looking for life beyond Earth.

Jim Green: I’m here with Dr. Laurie Barge, and she is a research scientist at the Jet Propulsion Laboratory. She’s also a co-lead on JPL’s Origins and Habitability Laboratory. Laurie is interested in the emergence of life on early Earth and understanding how to look for life out in the solar system and beyond. Welcome Laurie, to Gravity Assist.Laurie Barge: Thanks. Thanks for having me.

Jim Green: Well, how did you ever get interested in the study of how life may have originated on Earth?Laurie Barge: Well, actually, I had a more general interest in science when I was little, I just wanted to study space. But when I went to study that in college, I found that I was most interested in the things that address these existential questions like why are we here? And is there life elsewhere?

Laurie Barge: And so I ended up actually doing my thesis about biosignatures. So it was a reverse, it was why are these weird patterns forming and geological and chemical systems that look like life, but are not life? And then after studying that, I thought, “Well, can you go the reverse? Can you say, “Well, if a non-biological system can make such interesting patterns and complexity, then is this a way that you could lead from a geological system into a biological system at some point?” And so that’s why I switched over to studying the origin of life, which then also led me into studying Earth’s oceans.

Jim Green: So I hear your lab is really fascinating.

Jim Green: What does it look like when you walk in?

Laurie Barge: Well, it looks really different from what you would maybe expect, because we’re simulating something that’s at the bottom of the sea. But in order to do that, it looks like a mad science project. It’s all in what’s called a fume hood, because we have to keep the toxic gases away from the researcher. So those get sucked up into the fume hood. And then we have each little ocean vile separate on a stand being clamped up above the ground. And then we have tubes of atmosphere gas coming into each one, because we have to be early Earth, so we can’t have any oxygen in there. So we have tubes of nitrogen, and argon, and other non-oxygen gases feeding into each chimney.

 Laurie Barge and Erika Flores show off solutions that recreate the conditions of the bottom of the ocean billions of years ago.

Laurie Barge: The chimney itself, it looks like what’s called a chemical garden. There’s actually this whole other field of research called chemical garden where you can grow these plant-like structures from a metal salt. And they look like plants, but they’re completely non-biological. A hydrothermal chimney is also an example of a chemical garden, because it is growing from two solutions that meet each other and it grows vertically. So they look like mineral plumes, small chimneys, and they grow about a couple centimeters high, but of course, in their real environment, they can grow to be tens of meters tall. It’s just about what scale do you have as far as, for the fluid to inject into the seawater.

Laurie Barge: So the little chimney is actually connected with all these tubes, all these different things, and even instruments to analyze it as it’s growing. So it looks pretty cool.

Jim Green: Your research also focuses on hydrothermal vents. What are hydrothermal vents and where are they, and how do we know how life emerges from around them?Laurie Barge: Well, hydrothermal vents are basically cracks in the sea floor, where you have seawater that interacts with the sea floor rock, and then it goes down into cracks in the rock, and then it becomes chemically altered. So it’s basically a different fluid, then that hydrothermal fluid comes back up out of the sea floor. And when you have these two fluids interacting, you have the hydrothermal and the seawater, they’re very different.

Laurie Barge: And that’s why you get a lot of chemical precipitation of minerals, but you also get gradients forming.

Jim Green: So when you’re talking about gradients in the whole environment, what are you talking about?Laurie Barge: Well, we’re talking about really, just any big difference between the two solutions. You have the seawater and the vent fluid. And there’s a couple main differences that lead to important factors, for say, chemistry or life. One is the redox gradient. So this means that the hydrothermal fluid is emitting chemicals that are rich and electrons, things like hydrogen or methane. And so life can use these as fuel. And then the ocean, at least, today has oxygen in it. So that’s a great oxidant. And on early Earth, it would have had things like carbon dioxide, which is also an oxidant.Laurie Barge: And so that’s the redox gradient. And then you have chemical gradients. So these are just when you have a difference in the amount of a certain ion or molecule from the inside to the outside of the vent. So things like maybe sodium, or magnesium, or organic material. And then there’s also the pH gradient. So this is the gradient of how acidic it is. So the ocean on the early Earth would have been mildly acidic, and then the hydrothermal fluids, some of them are acidic, some of them are alkaline. And so each gradient can vary depending on what type of vent you’re in.

Jim Green: These hydrothermal vents actually is a relatively recent discovery. I think the first hydrothermal vent was found when I was in graduate school. So, I mean, this is just fantastic brand new research. But in each of these hydrothermal vents, don’t we find life?Laurie Barge: Yeah, these vents do support life. They support microbial life, but they can also support multicellular life. And it’s a little biosphere that’s supported by this chemical energy. It’s really interesting, because the vent is just giving off chemicals from inside the Earth that are energy sources for life, and life can build an entire biosphere based on this. And it’s separate from biospheres fueled by say sunlight. So the discovery of vents really taught us that you can have metabolisms of all kinds and they can be chemically powered by the planet, and then as we learn more and more about microbiology over the subsequent years, we’ve learned that life can actually use a whole variety of different energy sources. So, whatever there may be available in an environment, there’s probably some life that wants it.

Jim Green: Well, you know, since those hydrothermal vents were found, we’re now finding hundreds and hundreds of them. Where do we typically look in the ocean floor? Where is the biggest probability of finding a hydrothermal vent?Laurie Barge: Well, I would think that, I think generally, it’s where you know that there’s volcanic activity. And so things like the plate boundaries, mid-ocean ridges, things like that. You could expect that there’s going to be some chemical alteration. But they can be found in other places, too. And so it can be really hard to predict exactly where you should find a vent. So Earth’s sea floor is a very, very big place and it’s not completely explored. And so, there’s still a lot to look for.

Jim Green: So essentially, these vents don’t receive sunlight, they’re not powered by the energy of the sun, they’re powered by the energy of the planet. But our ocean isn’t the only body that has water like that. Where else do we think are hydrothermal vents in the solar system?Laurie Barge: Well, there has been discoveries of oceans on other worlds and we would like to find out if any of those might also have vents. And to have a hydrothermal vent, you need to have a liquid water ocean, but you also need it to be interacting with the rocky sea floor, because it needs to have the seawater going into those rocks and altering, and then coming back up. And so, basically, the questions for astrobiologists are, is there a rocky sea floor that is in contact with that ocean? And do you expect the ocean to be circulating and undergoing that same chemical process? And then, if it comes back up, what type of gradients do you have?

Jim Green: Now, the study of these hydrothermal vents that you’re doing so much in this particular area, is that because the basic idea is that life must have really occurred on Earth in the ocean first, and therefore these hydrothermal vents?

Laurie Barge: No one really knows the answer to that because with the origin of life, you can look at it from two directions. You can look at it from top down, which is where you look at all life on Earth and you say, “What does it have in common? What was the last common ancestor like?” And you can get some information, and then you can go bottom up and say, “Based on what we know of early Earth geologically, what was possible.” And then where does that take you? And ideally you want those two to meet up somewhere reasonable. And so, we don’t actually know where the first life lived, there’s theories that it could have been on land, underwater in a vent at a high temperature. And no one really knows the answer to that, honestly. So for origin of life chemistry, we have to test all kinds of different conditions and try to narrow it down. And then ideally, one of those, at least, will be similar to what we know about the earliest life.

Jim Green: So when you’re in the laboratory and you’re recreating a vent, what does that look like? Is that just a slit in the ground?

Laurie Barge: We make a little bottle that is the ocean. We make an ocean solution. And actually the nice thing about lab is you don’t have to be limited to the ocean that Earth has today. You can make early Earth’s ocean, you could make an early Mars guess at an ocean. So we make a little ocean, and then at the base of that, we inject, with a syringe, a little hydrothermal fluid. And if you slowly inject that, then those two fluids react and you can form mineral precipitates. And so, if you inject slowly and carefully, you can grow a little chimney in the lab, just like you see in vents in the field.

Laurie Barge: We make choices about how fast do we want the fluid to flow, how fast do we want the chimney to grow. And so, we control the situation more by having just one injection point at the bottom. So it really is a syringe needle that comes up the bottom, and then we control that injection. But if you make it different speeds or different forces, you can get all kinds of different effects on the chimney that you make.

Jim Green: Well, what are some of the processes then that are occurring besides the precipitation, as you say, there’s a reduction, and what does that mean chemically?Laurie Barge: Well, we have, let’s say, if we inject organics into the hydrothermal fluids. So we pretend they’re coming up from below from some water rock-chemistry, then those organics can react with the iron minerals in the chimneys, or even not just in a chimney, but around the chimney you have sediments and it’s like this big chemical reactor or fluid is flowing through a porous pile of mineral with so much surface area and so much pore space, so you can really get a lot of reactions. So one thing that we look at is reduction using that iron to reduce organics into other molecules, and then also trying to form those building blocks of life, like amino acids.Jim Green: Oh, wow. So you actually can form amino acids in these environments? Are there some specific conditions or temperature ranges that you’re finding out are really critical to be able to do that?Laurie Barge: We are finding that for amino acids specifically, it is good to have more minerals than less minerals. So it’s nice to have a nice pile of sediments, or a really a big chimney rather than something small. And we find that it works a little bit better when you’re at a more alkaline pH and when the temperature is medium high, like maybe 50 to 70 degrees, not too high. But a lot of times in lab, you find the “best condition” for a reaction, but that’s not actually the condition that Earth had. And so, you have to say, “Well, what’s the best condition?” But also, “What’s the most realistic one?”

Jim Green: Well, you know, Mars, in its distant past, when Earth was a blue planet, Mars was a blue planet, around four billion years ago, it actually had a huge ocean. Two thirds of the Northern hemisphere was under water, but that water’s gone. So can we, or should we roam around that ancient ocean floor of Mars looking for old hydrothermal vents? Would that be a good idea?Laurie Barge: I think that’d be a great idea. I would like to see that. I would like to see some roving around looking for evidence of old vents, but also if you can get underground at all and look and see what’s there. On Earth, we do this, we look for the oldest rocks and say, “What do they say about our ancient ocean?” So being able to do things like that for Mars and other planets would be amazing.

Jim Green: Well, if you could invent a spacecraft to find the type of life that we’re talking about, which would be extremophile, living in extreme areas like high pressure vents and high temperature ocean world, what would it be like? And where would you go?Laurie Barge: Well, I think there’s so many places you could go. And I would personally want to see things like how we study Earth’s ocean. So we have robots that go underwater and look at vents. And even on Earth, where it’s the easiest possible scenario for a planet, because we’re here, it’s still really hard to explore the ocean. And there’s a lot of work still to be done about understanding our sea floor. So, I would love it if we could ever get to the sea floor of another world that might have vents, even though I know that would take perhaps many missions or many years to actually characterize that environment. But if we could ever go to a vent with a robot and actually look at it and see, does it have life? Or could it support life? Or what does it even look like? I think that would be fascinating.

Jim Green: On Gravity Assist, we also get questions from our listeners, and one of them, I think you’re going to be able to answer, and that is, “Do you expect evolutionary rules to be universal? Or would extraterrestrial life just follow its own rules?”

Laurie Barge: I would say, probably in general, some things are the same, like the fact that certain chemical elements are going to be better energy sources for life, or maybe the way that organic chemistry might have to work for mutation. But I think that also evolution is largely directed by the environment and the planet. And so, on another world or with another origin, you would also have to ask, “How is that planetary environment and the evolution of the planet affecting its life as well?’

Jim Green: Another listener wanted to know about the similarity of genetic material across all of Earth’s life form, they appear to be the basis for a single origin of life. But could that similarity of genetic material also indicate that life can only form in one manner?

Laurie Barge: I think we don’t know for sure how many origins of life there could have been. All we know is that all life on Earth has one common ancestor. But we don’t know what happened before that. And so it is possible you had other origins that either fizzled out or something. But also, it’s interesting because if you did have multiple origins, and if it was the case that life could only happen one way, then you might expect a tree of life that had more than one ancestor. And so that’s something that we can look of when we see life on other planets as well.

Jim Green: Well, I found out that one of the things that you like to do through a National Science Foundation program is to work with summer students. What are some of the things that you do?

Laurie Barge: Yeah. It’s actually a year-round program. Well, it was called Bridge to the Geosciences. And so we design modules for community college students to learn about different careers in geoscience or in STEM. And so we would go to different institutes and show them what are the types of jobs you could have as a geology major or as a science major, beyond just say, being a professor at universities. There’s all kinds of really interesting things that one can do with that. So we try to give them a more broad view of what this looks like while they’re still in school.

Jim Green: Well, Laurie, I always like to ask my guests to tell me what was the event, or person, place, or thing that happened that got them so excited that they became the scientist they are today. I call that event a gravity assist. So Laurie, what was your gravity assist?Laurie Barge: Well, honestly, I would say it was the missions that went on during my childhood and also when I was in college. And so for me, I think the first time I thought I really decided I was going to work for NASA was when the Voyager mission passed Neptune. And I forgot what year this was, but I was in elementary school. And so, I remember seeing that on the news and thinking, “Wow, this is great. I should work for NASA.” And at that time I had no idea what astrobiology was, or that I would end up liking geology or chemistry or any of this. But it was what put it on my radar.

Laurie Barge: And then when I was in grad school, the Mars Rovers, Spirit and Opportunity landed. And so, that was really fun too. And Cassini got to Saturn at that same time. So it was really fun to be studying my research as these missions were studying these planets. And so, I think the missions were very inspiring, and I think they have been for a lot of people in my cohort.Jim Green: Well, thanks so much for joining us today and talking about a real passionate topic you have, the origin of life here on Earth. Because if we don’t understand it, how it happened here, how can we possibly find it elsewhere? Thanks so much, Laurie.Laurie Barge: Thank you.Jim Green: Well, join me next time as we continue our journey to look for life beyond Earth. I’m Jim Green, and this is your Gravity Assist.


Lead producer: Elizabeth Landau

Audio engineer: Manny Cooper