The lucky breaks that make our Earth home

[THEME MUSIC] FLORA LICHTMAN: Hey, it’s Flora Lichtman, and you’re listening to Science Friday.

Think back to earlier in the month, when the Artemis II astronauts sent back those spectacular pictures from their trip around the Moon. There were a couple of shots of Earth that really made us think of Carl Sagan’s comments on the “pale blue dot.” “That’s home. That’s us.” And with this being Earth Week– happy Earth Week to all who celebrate– we thought it’d be a good chance to get the big picture. The really big picture. What makes Earth so special, and why are we here at all?

Joining me now is astrophysicist Hakeem Oluseyi. He’s author of Why Do We Exist? The Nine Realms of the Universe that Make you Possible.

Welcome back, Hakeem.

HAKEEM OLUSEYI: Thank you so much for having me.

FLORA LICHTMAN: We love having you. I have to say, what I loved about your book is that you broke my concept of what’s needed for life. You took me way beyond atmosphere or water. So I want to start big. If you’re a universe, how do you build a place where we can live? I’m guessing, you need a sun, right?

HAKEEM OLUSEYI: You need a sun. And for sun, you need these giant clouds of hydrogen. This is the sole source material from which new stars are made. They’re called giant molecular clouds. And they’re light years across. And they birth hundreds and thousands of stars, but they themselves must come from somewhere. And it’s a huge coincidence that we have this little thing called a proton and a thing called an electron that just happen to have, even though they’re so different, one from the other, equal and opposite electric charges. And so, if electrons didn’t exist, every proton in the universe would try to get as far apart from every other proton as possible. But when they bond with an electron, they can be gathered into these gargantuan clouds, and then birth stars.

FLORA LICHTMAN: OK, so you’ve got these big clouds, and then the matter collects. It’s kind of like dust bunnies.

HAKEEM OLUSEYI: Yeah, it’s kind of like dust bunnies. And there’s a player in the scheme that doesn’t get a lot of attention. And that’s called turbulence. Inside these clouds, you get these knots of denser material. And turbulence makes them swirl and concentrate, and they form these long filaments that break up into clumps, that break up into cores that eventually try to form stars.

FLORA LICHTMAN: Wow. OK, so that miracle happens. You’ve got a sun. Now, we need a planet.

HAKEEM OLUSEYI: Yes.

FLORA LICHTMAN: How did we get this one?

HAKEEM OLUSEYI: Well, in a way, can say that we’re made from the residue of the residue of the residue, right?

FLORA LICHTMAN: That sounds right, Hakeem. Just knowing us.

HAKEEM OLUSEYI: Because in the early universe, what happens is when matter comes into existence, it’s almost equal amounts of matter and antimatter. And when matter and antimatter meet, just like in the power system for the Starship Enterprise, the matter-antimatter conversion chamber, those two matter particles cease to exist. Their mass is converted into energy in a process called annihilation. And for every billion particles, there was one matter particle left over. And that’s where we’re made from.

And then when you get to the level of the universe as a whole, matter that know of is only about 5% of all that exists. 95% is the real universe. We’re that leftover 5%. And in the same way, when a star forms, there’s residual matter left over that forms a disk around that star. And again, the forces of electromagnetism, like dust bunnies, begin to pull particles together. And then they begin to collide and grow, and eventually, you have dozens of protoplanets orbiting that star that then begin to collide and grow even more. And hopefully, the system settles down. You have your planet orbiting your star. And now, if everything is right, you’re ready to seed life.

FLORA LICHTMAN: Yeah, but this was another big aha. Like, it’s pretty hard to get everything right. And I think we pay a lot of attention to things like temperature and the presence of liquid water. But there are all these other amenities that make Earth real estate valuable.

HAKEEM OLUSEYI: Oh, absolutely.

FLORA LICHTMAN: Talk to us about them.

HAKEEM OLUSEYI: Absolutely. So your star needs to be in the right part of the galaxy to form life, right? In our galaxy, there’s this 4 million solar mass, supermassive black hole at the core of the galaxy, and all galaxies have these supermassive black holes. So those areas aren’t safe so you have to be far enough away. And scientists have studied what percentage of our stars are in what we call the galactic habitable zone. And for the Milky Way, it turns out to be only 1.2%.

FLORA LICHTMAN: Because we’re not even talking about how close you are to your sun.

HAKEEM OLUSEYI: No, we’re talking about where your sun is located within its galaxy. If it can be–

FLORA LICHTMAN: Yes.

HAKEEM OLUSEYI: –if it can be safe.

FLORA LICHTMAN: Beyond location, location, location, you talk about some other special features that are required, like the magnetosphere, which I haven’t given a lot of thought to.

HAKEEM OLUSEYI: Yes, the magnetosphere is again an unsung hero in our story. So we’re lucky on Earth because we have this three-layer filter that not only allowed life to thrive, but allowed life to leave the oceans and come onto land. So what is that three-layer filter? First, have our atmosphere, which in itself is an anomaly. Then you have in our atmosphere, an ozone layer. Again, powered by life. Without life, there would be no ozone layer. But you needed billions of years of simple photosynthetic oxygen-producing life to have an ozone layer.

But extremely importantly, wouldn’t have the atmosphere if we didn’t have our planet’s powerful magnetic field. And that’s what sets us apart from Venus and Mars. Because when we look around the universe, when we look around our galaxy, when we look around our solar system, atmospheres typically come in one of two configurations– super thick or absent or completely absent, just no atmosphere.

But here is Earth, with this super thin atmosphere that allows the life-giving light in, but repels the damaging radiation that would make life on Earth impossible. And not only that, that same radiation would have done to Earth what it did to Mars, and that is erode our atmosphere away, such that life could not exist on the surface of our planet.

FLORA LICHTMAN: And that magnetosphere is because of how the planet was formed?

HAKEEM OLUSEYI: That is correct. Early in Earth’s formation, it was struck by a Mars-sized body that we’ve given the name Theia. And instead of our core settling down and becoming layered with denser stuff in the middle and less dense stuff as you go out, what happened with Venus, that collision stirred up our core of our planet. And the result today is that there is not solid ground completely under your feet from the surface of the Earth down to the core.

Our planet is more like a lava cake. We have a molten liquid outer core, which I don’t think people appreciate. It’s like we have a solid inner core. You can think of that as a large nut surrounded by molten chocolate, surrounded by to the mantle and the crust. So maybe–

FLORA LICHTMAN: You’re speaking my language. Thank you.

HAKEEM OLUSEYI: That’s right. Galactus would find Earth incredibly delicious. So because of that molten core, that molten outer core, where it interfaces with the mantle, there is a big temperature difference. The mantle is cooler, the outer core is hotter. So that means that heat wants to flow. And just like in a convection oven or a convection heater in your home, that stirs up that molten core. And when you have liquid metals flowing, they create magnetic fields. And that liquid outer core creates the strong magnetic field of Earth. and it would not exist had we not had that massive collision with Theia.

FLORA LICHTMAN: After the break, we are going to get to the life part. Stay with us.

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OK, let’s talk about life itself for me. I feel like we’ve all heard about the building blocks of life, but you also call out some other important ingredients, like having a cell membrane.

HAKEEM OLUSEYI: Yes.

FLORA LICHTMAN: Why is that so important?

HAKEEM OLUSEYI: Well, life needs to do the opposite of what the rest of the universe is doing. And that is, life needs to create organization, and life needs to create energy gradients such that instead of spreading energy out, it concentrates it. And in order to do that, it needs to separate itself from the rest of the universe. And so the cell membrane, which on Earth are these fatty molecules that we call lipids, that have this particular property that one half of them likes water and the other half doesn’t. So when they are in water, they arrange themselves in little spheres so that the side that does not like water is on the inside and the side that does is on the outside.

So now, you have this separate compartment from the universe in which chemical reactions can take place. And some of those chemical reactions are involving these organic molecules. And the thing, again– I will say it again– we find these organic molecules on asteroids, comets, and gas clouds. They’re everywhere.

FLORA LICHTMAN: So they can spontaneously assemble. That’s the idea.

HAKEEM OLUSEYI: They do spontaneously assemble. And not only that, the important organic molecule that we call RNA, experiment after experiment after experiment shows that they also will spontaneously form under the right conditions of energy and temperature and being in a nice, little compartment.

FLORA LICHTMAN: But here’s where I get stuck. So how do we go from a water bag with a shell, with some complex molecules inside of it, to a cell that has organelles that do jobs?

HAKEEM OLUSEYI: Well, there’s one step in that process that we call abiogenesis, that is a Nobel Prize waiting for someone to figure out exactly this process.

FLORA LICHTMAN: Get on it. Abiogenesis, what is that?

HAKEEM OLUSEYI: That is the step where you go from non-living inanimate matter to actually living reproducing matter.

FLORA LICHTMAN: Is this like where physical principles meet natural selection? Know what I mean? I guess, I’m wondering why molecules tend to reproduce themselves.

HAKEEM OLUSEYI: There are examples of non-living matter reproducing itself. The simplest example is a crystal. Crystals reproduce themselves. We take advantage of that when we grow the silicon wafers that we use for our electronics. But the process of– if you think about the nature of life, it’s both stable and unstable. It’s stable in the sense that a cell can last for a long time. But in order to reproduce, it has to split in half, so that’s the instability side of it.

And so if you think about a situation like at a black smoker, these volcanic vents at the bottom of the ocean have hot water coming out of the vent, and then you have cold water surrounding it. So you can imagine that such a cell, while in the cold water will be stable, but when it hits the hot water, it may break apart. So these are the very sort of environments that we think early life may have started. And that’s just an example of how you can use temperature differences to have that stable yet, unstable property.

But in terms of that first cell that decided, hey, I’m going to do metabolism, I’m going to split in half and make a copy of myself, I don’t know what the foremost leading authorities, because I’m not one of them on that topic. But far as I know, have no idea how that step took place.

FLORA LICHTMAN: I feel better. Hakeem, the thing I felt reading your book–

HAKEEM OLUSEYI: Yes.

FLORA LICHTMAN: –was just like, how profoundly miraculous it is that I’m here at all, that you and I are having this conversation right now. It just seems, so improbable. Don’t know. My mind can’t really even hold it.

HAKEEM OLUSEYI: I see it as Improbable, but inevitable. Because the universe does things in big numbers.

FLORA LICHTMAN: Yes.

HAKEEM OLUSEYI: Our galaxy has 400 billion stars or so, and there’s hundreds of billions of galaxies in the observable universe alone. And so, if you look at many of the steps necessary, the universe creates greater and greater complexity as it evolves. That’s just what it does. And so we are a step on that complexity ladder.

So it seems to me that the step of creating those early cells is about potential. And once you have that potential, you’ve that possibility. And given the large numbers of planets and stars and galaxies, it becomes an inevitability. But how do you go from there to large multicellular life and then to intelligence, that is where you need that water bathed in sunlight. And most places where you have life, that’s not going to happen.

And even if you have large multicellular life, it still took 500 million years for us to get humans that are technologically advanced. So I think you and me having this conversation as humans with language, oh, man, that’s incredibly rare. That is incredibly rare. But when it comes to multicellular life, planets orbiting stars, I calculate that it’s like one out of a million in our galaxy. So there should be about 100,000 stellar systems in our galaxy that have multicellular, complex life.

FLORA LICHTMAN: Amazing. Before we go, you write a lot about imagination.

HAKEEM OLUSEYI: Yes.

FLORA LICHTMAN: I loved that. What do you think the role of imagination is in science?

HAKEEM OLUSEYI: Imagination is our superpower, especially when we employ our hive mind and bring multiple imaginations together. Before anyone can do anything, they have to first imagine it. You have to sit there, whether it’s mathematically, whether it’s building an experiment, whether it’s deciding where to look in the universe. We have the ability to imagine things that have never existed in the universe.

And if you go all the way back to Galileo, he realized that, yeah, what we accept is true only is, it must be consistent with what we observe to be true. But in order to– and when I say observe, I mean in our experiments and our observations. But in order to get to the deepest truths of the universe, we need to imagine things that we could never do experimentally. So our imaginations are the gateway to the future and to the greatest truths that the universe has to offer.

FLORA LICHTMAN: Happy Earth Week, Hakeem.

HAKEEM OLUSEYI: Thank you so much. You as well, Flora.

FLORA LICHTMAN: Astrophysicist Hakeem Oluseyi is author of Why Do We Exist? The Nine Realms of the Universe that Make you Possible. And you can read an excerpt from the book at sciencefriday.com/exist.

Speaking of Earth Week, we recently got a call from a listener about other planetary issues.

ANDREW: Hello, my name is Andrew calling from Sacramento, California. Was just finishing listening to the episode titled, “Should Pluto to be a planet again?” And one thing I noticed that the scientists, they called it Mother Nature, as far as the formation of the planets, and how their surfaces are, and things like that. It’s very rare that I hear people refer to Mother Nature in reference to other planets, other than Earth, which I really liked. Because Mother Nature is the universe, not just Earth. It’s a nice reminder. So thanks for that.

FLORA LICHTMAN: Thank you for calling us, Andrew. And if you have a thought or an observation or a question for us, even like the biggest, most giant, most existential one, please give us a ring. 877-4SCIFRI is our number, and we’ll see what we can do. This podcast was produced by Charles Bergquist. Thank you for listening. I’m Flora Lichtman.

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