The Earth is teeming with life, both in the upper atmosphere to kilometers underground. There’s no question that our planet has life. But is our planet itself alive? This is a question posed back in the 1970s as the Gaia hypothesis, and it got its share of criticism. Some new ideas have been proposed to bring this hypothesis to the modern era.
Gaia hypothesis (Wikipedia)
PSI’s David Grinspoon Explores ‘Planetary Intelligence’ (Planetary Science Institute)
Life as We Do Not Know It by Peter Ward (Penguin Random House)
Are Viruses Alive? (Microbiology Society)
What is the carbon cycle? (NOAA)
The Water Cycle (NASA)
Chris McKay (NASA)
What is a biosignature? (NASA)
Understanding the K-T Boundary (Lunar and Planetary Institute)
Astonishing Heat Grips India and Pakistan (Scientific American)
Transcriptions provided by GMR Transcription Services
Fraser: Astronomy Cast episode 641. Are planets alive? Welcome to Astronomy Cast, your weekly facts-based journey through the cosmos where we help you understand not only what we know, but how we know what we know. I’m Fraser Cain, publisher of Universe Today. I’ve been a space and astronomy journalist for over 20 years. With me as always is Dr. Pamela Gay, a senior scientist for the Planetary Science Institute and the director of Cosmo Quest. Hey, Pamela, how you doing?
Pamela: I’m doing well. It’s weird getting to the point in our lives where various elements of our life are now 20 years old. In September, my PhD turns 20 years old. I’m not used to this yet.
Fraser: Yeah. But haven’t you noticed, I don’t know, I guess this is what it feels like to be in the old boys’ club. Whatever is the astronomy equivalent of that. You have connections. You have references. People know who you are. I’m able to reach out to people to do interviews, and they’re like oh, Fraser, I’ve been a big fan of your work for 10 years. I’m like, wait, what? You work with this really cool space craft. You know who I am? And they’re like, yeah, I’d be glad to do an interview. Or, someone will reach out with a piece of news. I’ll have a source, and again, it’s just like out of the blue. And you’re like, wait a minute, what?
So, doing the same job, showing up day after day for 23 years does have its advantages. I highly encourage people to stick with something for a while if it’s working for them. The benefits add up overtime.
Pamela: I agree with all of that. The other side of it in astronomy is no one ever retires, because they love their jobs, which means that all the people who were senior people, who were hired during the Apollo era when I was a graduate student, they’re still here. So I’m still running into the people that met me when I was a crazy eighth grader doing astronomy. And they’re still researchers.
Fraser: And in many cases looking out for you and sending interesting information your way. It’s cool. It’s a great community in general.
Pamela: And occasionally finding pictures from when I was in eighth grade in their office when they clean it out. That has happened. It was very strange.
Fraser: That’s very weird. All right. The earth is teeming with life from the upper atmosphere to kilometers underground. There’s no question that our planet has life. But is our planet itself alive? This question posed back in the 1970s is a Gaia hypothesis, and got a share of criticism. But some new ideas have proposed to bring this hypothesis into the modern era as we search for exoplanets. All right, Pam. It just sounds like even a ridiculous question. Is our earth alive? Come on. Is our planets alive? Like, they’re rocks covered in this thin goo that is life. What does it mean to say is a planet alive?
Pamela: So, I have to start from the beginning with this episode is very much inspired by Dr. David Grinspoon. He goes by drfunkyspoon over on Twitter. And a talk he gave that we’ll link to in the show notes that asks this question, is the earth alive, is a planet alive? And the way he phrases it really got me. Because he asks the question is life something that happens to a planet or is life something that happens on a planet? He phrases it much better in his talk. And he points out how with individuals, if you break things down smaller and smaller and smaller, you end up with things where it’s like, can you really consider this bit of life alive? Is a molecule alive? Well, maybe if you’re looking at DNA it can replicate.
Pamela & Fraser: Is a virus alive?
Pamela: And the smaller you get, the weirder it is to ask is something alive? The bigger something is, you start to run into questions like is an ant colony a single life form or multiple life forms in the grand scheme of how it works? There are corals and many other ocean—many other life forms of the ocean. Fraser’s dying laughing at me. I gave up. I had to give up on the word.
Fraser: That was a valiant attempt. Oceanic, maybe?
Pamela: Yes, that’s the word I can’t say this morning. There’s many life forms in the ocean that are individual bits that have gathered together to grow into structures. Fungus has this often. And so, when you look at a slime mold solving a maze, which part is the life form, the entirety of the slime mold or each of those little, tiny single-celled organisms that are capable of reproduction into this mold? So, when you start looking at a planet, it’s made at the most basic level of rocks, if it’s a rocky world like earth. And a single rock, not so much alive.
Fraser: When you think about this idea of even just our own bodies, are we alive or are we just a meatsuit for the bacteria that has colonized our gut and they just are driving us around like some kind of mecca? That’s what I wonder. Is it me or am I just the bacteria talking?
Pamela: The author of the book Life as We Don’t Know It, Peter whose name will be in the show notes. For those of you listening and not watching live, we are recording this at 10:16am on a Tuesday morning, and I am not a morning person.
Fraser: Pamela is not caffeinated enough.
Pamela: Yeah, and I heard him giving a talk. I loved his book, sought out a talk. He pointed out a fact that will haunt me forever. The human body has on it and inside of it more individual bacteria, microbes, other tiny life forms, parasites if you’re particularly unlucky, eyelash lice, all of these other things that outnumber the number of cells that are created by our DNA. That’s outstanding, and not in a good way.
Fraser: All right. So, what is the planetary version of a bacteria’s meatsuit?
Pamela: So what David points out in his work, and he’s working with a whole group of collaborators, as you add more and more rocks together, you get to a world that is capable of having essentially circulation. When you look at the flow of heat from the core of a planet through the crust, it is capable of feedback mechanisms. And this all builds on early work by Lovelock and Margulis about the Gaia hypothesis where they looked at our world’s ability to recover chemically into a thermo-equilibrium, a chemical equilibrium over and over and over again.
Catastrophes can happen and throw our system out of sorts. But overtime, these different feedback mechanisms always bring us back to a stable condition. So far, Venus is an example of what happens when you find a new thermo-equilibrium that is not where you wish you would be.
Fraser: But you’ve got all these cycles, right? You’ve got the carbon cycle, you’ve got the water cycle, you’ve got various air, atmospheric, earth cycles all working together, regulated perhaps by life, that is keeping—as things get a little out of whack, as there gets too much carbon, then plants grow, they sequester that carbon, bring the temperature back into what makes life happy. So is life calling the shots within their capability of keeping the planet where life wants it to be?
Pamela: And this is where it starts to get very interesting because as I said, we saw in Venus. It reached an alternative point of thermo-equilibrium at one point in its evolution, where something catastrophic happened, depending on which paper you read from hundreds of millions of years ago to a couple billion years ago, that took it from having an earthlike with perhaps vast oceans to being the sulphuric acid raining hellscape we see today.
Fraser: And same with Mars, when you think about it. Like it was too small, too cold, too dry, but maybe again, a long time ago, it was warmer and wetter, could’ve been covered with life. Life again could’ve been trying to keep the planet habitable for itself. And it couldn’t keep up, and eventually it entered a new temperature regime.
Pamela: And here I think Titan might be a more interesting comparison than Mars, because Mars didn’t have at any point sufficient gravity to be able to permanently hold onto all of its atmosphere, and it certainly doesn’t have the magnetic field necessary to hold onto its atmosphere. So, life did not have the potential to hold it into an earthlike climate. Titan does not have an earthlike climate. It exists at the triple-point of methane, where you see methane existing as a gas, a solid, and a liquid at various points in the environment. There are lakes of ethane and methane.
And, there has been interesting work done by Chris McKay in the past looking at how some of the chemicals in the atmosphere don’t appear to be in a permanent equilibrium state. They need to have things getting fed into the system. So it raises the question of, is life on Titan keeping it in an alternative equilibrium or are there geologic processes keeping it in an alternative equilibrium?
Fraser: Well, this kind of leads into my next question, which is like, what are the implications of this idea for the search for not only habitable worlds, but worlds that have life on them?
Pamela: So, when you start looking at worlds that like earth, are in a chemical equilibrium that chemistry alone can’t explain. You can’t explain the oxygen in earth’s atmosphere strictly by mixing things together and letting them evolve over time and putting them in the UV of the sun’s light. You instead end up with lots more carbon-based gases, so carbon-dioxide, carbon-monoxide, all that sort of stuff. You don’t end up with the methane that we see because that breaks down in sunlight.
So, when you start to look at a system that diverges from a you mix the chemicals together and see what happens kind of equilibrium, you know there has to be other driving forces present. Something that is maintaining well, respiration is one way to think about it, maintaining metabolism, is the word that Grinspoon used a lot. So, we have on our world bacteria, plants, animals, everything from all the animal kingdoms—and that’s not the right word I don’t think, but from all of the kingdoms of life, we have things that are metabolizing their environment and changing the chemistry because of their life.
Fraser: I’ve got an interesting perspective because as you know, we’re in the process of trying to rehabilitate a piece of land that was logged and burned and scoured to just bare, dead dirt. You can see this process of colonization of the various plants happening. There’s certain first plants that can live almost anywhere that are able to grow, and able to start. Some of them are very invasive and we need them gone. They don’t come from these parts. But, you know, they come from Europe — Scotch broom is the worst. It’s just this awful, terrible plant that can take over anything and just blocks out everything. But it’s a fast mover. It’s first in.
And then you can see the grasses are starting to grow. And as the grasses grow, you get this layer of soil, and now more complicated, more fragile plants are starting to grow up where all the places where the grass has been able to get a foothold. And this idea of looking for biosignatures, I think astronomers have given up at this point saying okay, if we see methane in the atmosphere of an exoplanet, then there’s life there. If we see oxygen, then there’s life there. And in fact, I know we can go back to early episodes of Astronomy Cast, and you said those exact words.
Pamela: I know.
Fraser: If we see ozone, or if we see oxygen, then there’s life there. That idea is hilariously simplistic now. That we are now at the point where it’s not just one chemical, it is a mixture of a collection, a dozen, that you’re gonna see a large number of individual signs in balance with each other demonstrating this idea that this planet is alive. That it is undergoing some kind of self-regulation, metabolism, what have you, that is the signal we are going to have to be looking for as we search for life beyond earth.
Pamela: And what constantly gets me is how after past ecological disasters, the K-T boundary being the one that most comes to mind because I’m still obsessed with the new Tanis findings, our world got smacked by a large rock from space that lifted debris back up that then came back down through the atmosphere, and turned our atmosphere into an oven. It baked our ecosystem. But there was enough stuff buried under the soil and deep enough down in the water that it was able to come back in and say, okay, we’ve got the top layers of the soil. We’ll repopulate. We will start over and make things habitable again. And it took time, and then we ended up with giant, scary mammals for a while.
Fraser: So, I wonder, you talked about the K-T, the dinosaur killing asteroid. We’ve had just these horrendous volcanic eruptions in the past. We’ve had ice ages. We’ve had potentially horrible gamma ray bursts hit the planet. Who knows what kind of things. And yet the planet has always bounced back and it’s always bounced back to a state of equilibrium that perfectly matches the temperature regime that the earth is in, where it is in the habitable zone. And it feels like the distance from the sun is setting—or the amount of radiation the planet is receiving is kind of setting where that set point is that life’s gonna try to reach with various boundaries.
Pamela: I would say the distance from the sun is aiding and abetting in picking the temperature we are at equilibrium within. Anyone who has gotten into a car in the summer knows the greenhouse effect can be a terrible thing. And we could have reached a much higher equilibrium temperature than what we’re at. We also could’ve ended up at a much lower equilibrium temperature than we’re at if the conditions that drove various glaciation periods had been maintained.
What is fascinating to me is life seems to be optimized for basically the tropical temperature regime where you never get below freezing. Life can exist below freezing, but it’s optimized for that temperature regime where you’re below freezing but it’s not so hot that you have moisture baked out of every single substance. And in that temperate regime where life is able to thrive, you see the desire to take the planet out of equilibrium stop. But when you go colder than that, you have life trying and trying and trying, and it’s outputting the kind of stuff that will gradually raise the temperatures up. So, it has taken catastrophic events in general to drop the temperatures. And then life has brough the temperatures back up to an equilibrium. And then something catastrophic happened. And it got dropped down.
And that’s one of the things that’s particularly terrifying about global warming, where we’re seeing temperatures in the 40s and 50s Celsius, 140s and 150s Fahrenheit in India.
Fraser: Oh, what a nightmare!
Pamela: Yeah, it’s going to destroy agriculture at a time when agriculture is being affected by so many other issues. And they don’t have the infrastructure. There’s going to be massive loss of life. And this isn’t the kind of thing where the bacteria are going to be like, we are pleased, we are going to do everything we can to release gases to drop the temperature of the world. That’s not a feedback mechanism we necessarily have. So, we’ve gone out of equilibrium in a direction that may force us to, like Venus, find a new equilibrium we don’t like. Let’s not—can we work on that one?
Fraser: Let’s not run that experiment? Yeah. So, I guess, what are the implications? Like what does Grinspoon and team feel like this direction of thinking about planets, whether they’re alive or not, how will that help us in our science?
Pamela: Thinking of planets of systems that are metabolizing, that have reached specific levels of equilibrium, allows us to start looking at questions of astrobiology more clearly. Question of, okay, so if we have different kinds of life, what are the kinds of new equilibriums that we can reach? What are the kinds of new chemical balances we can expect to see? It allows us to ask deeper questions in terms of just, how do we protect our own world, where we know with a human being, you have to keep certain processes in balance. Your kidneys have to work, or you die. You have to be able to remove the pollutants from your system. Well, with a planet, what does it take to kill a planet? How do we perform dialysis on a world like earth?
That’s not a phrase that Grinspoon used, but that’s the kind of questions that seem to evolve naturally from the work that he’s looking at.
Fraser: But could it be as simple as —sorry— just like checking the temperature of a planet? Like, Venus and earth are not that far apart. And yet Venus is like, almost 300 Celsius. No it’s more, more than that. 450 Celsius? Anyway, it’s hot. Really hot. Hot enough to melt lead, as they say. And yet earth is just a little farther away, and the average temperature on earth is very cool.
Pamela: Venus averages out at 464 degrees Celsius. That’s 867 Fahrenheit. Earth averages out at 59 Fahrenheit, which is 15 Celsius.
Fraser: 15 Celsius? And how much of that is life’s fault? That planet earth, at its position in the habitable zone, without life, would earth have hit this runaway greenhouse effect, like Venus, and be 200 Celsius as opposed to 450 Celsius?
Pamela: Right. Or never recovered from glaciation.
Fraser: Right, right. And so I wonder, maybe it’s a very complicated—like you’re measuring all these very complicated things, or maybe it’s something really simple. Just, the temperature is 20 degrees. Life had to be regulating the temperature on that planet. I wonder.
Pamela: And these are the questions that we have to ask. Do you view a system like a planet as metabolizing, and if you do, what does that mean? And I really think viewing a world as metabolizing allows us to say, yeah, those temperatures, those chemistries, those mean there is an ecosystem. And these other ones mean, well, that planet may still have tectonics. But it’s environment may have life, but the life isn’t moderating the environment.
Fraser: Right. The life isn’t in control of a planet. Yeah, really interesting. Very cool. Well, thank you, Pamela.
Pamela: Thank you, Fraser. And thank you to all of our patrons out there. We couldn’t be here without you. And as we mentioned last week, we know a lot of you are starting to get really affected by the inflation that is gripping everything. And to those of you who are still out there donating and able, we are even more grateful than often. I mean, we’re always grateful. I don’t know how to phrase this. I’m going to give up, and I’m just gonna thank people.
This week, I would like to thank Ronald McKay – sorry, Ronald McCoy, Stuart Mills, Dave Masefield, Helge Bjøkhaug, Thomas Sepstrup, Mountain Goat, Stephen Veit, Burry Gowen, Jordan Young, Kevin Lyle, Jeanette Wink, Andrew Poelstra, Venkatesh Chary, Brian Cagle, David Truog, TheGiantNothing, Aurora Lipper, David, Gerhard Schwarzer, Buzz Parsec, Ronald McCoy again, J.F. Rajotte, William E. Kraus, cacoseraph, Robert Palsma, Laura Kittleson, Jack Mudge, Les Howard, Joe Hollstein, Frank Tippin, Adam Annis-Brown, Gordon Dewis, Richard Drumm, and Alexis.
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Fraser: Thanks, everyone. We’ll see you next week.
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