Science Friday - The lucky breaks that make our Earth home

Episode Date: April 21, 2026

What makes Earth special, and why are we here at all? In his book “Why Do We Exist? The Nine Realms of the Universe That Make You Possible,” astrophysicist Hakeem Oluseyi tackles the conditions needed to put life on Earth, from the formation of stars, to self-organizing molecules, to quantum weirdness and the nature of time. He joins Host Flora Lichtman to celebrate our place in the cosmos.  Read an excerpt from "Why Do We Exist?" Guest:  Dr. Hakeem Oluseyi is an astrophysicist and author of “Why Do We Exist? The Nine Realms of the Universe that Make You Possible.” Transcripts for each episode are available within 1-3 days at sciencefriday.com. Subscribe to this podcast. Plus, to stay updated on all things science, sign up for Science Friday's newsletters.

Hey, it's Flora Lichten, 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. You know, 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 Olushei. He's author of Why Do We Exist, The Nine Realms of the Universe, that make you possible. Welcome back, Hakeem. Thank you so much for having me. 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. Like, you took me way beyond atmosphere, 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? You need a sun. And for a 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, you know, hundreds and thousands of stars. but they themselves must come from somewhere.

And, you know, it's a huge coincidence that, you know, 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, you know, 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 Earth stars. Okay.

So you've got these big clouds, and then, like, the matter collects, right? It's kind of like dust bunnies. Yeah, it's kind of like dust bunnies. And, you know, 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 in the cores that eventually tried to form stars.

Wow. Okay. So that miracle happens. You've got a sun. Now we need a planet. Yes. How did we get this one? Well, in a way, you can say that we're made from the residue of the residue of the residue, right?

That sounds right, Hakeem. You know, just knowing us. Because in the early universe, what happens is when matter comes into existence is 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-antimatic 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 we know of is only about 5% of all that exists. 95% is the real universe, right? Where are that leftover five? 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 proto-planets 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. Yeah, but like this is another big a haze.

It's pretty hard to get everything right. And I think, you know, 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. Oh, absolutely. Talk to us about them.

Absolutely. So your star needs to be in the right part of the galaxy to form life, right? In our galaxy, there's this four million solar mass, supermassive black hole at the core of the galaxy, and all galaxies have these supermassive black holes. So, you know, 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%.

And because we're not even talking about how close you are to your son, right? No, we're talking about where your son is located within its galaxy, if it can be safe. Yeah. Yes, if it can be safe. Okay. 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. 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 on to land. So what is that three-layer filter? First, you 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, you 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 have 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 very 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. And that magnetosphere is because of how the planet was formed, right? That is correct. Early in Earth's formation, it was struck by a Mars-sized body that we've given the name, Thea.

And instead of our core settling down and becoming layered and, you know, with the denser stuff in the middle and less dense stuff as you go out, like 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, right? 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 like a large nut surrounded by molten chocolate surrounded by the mantle and the crust. You're speaking my language. 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 them. After the break, we are going to get to the life part. Stay with us. Okay, let's talk about life itself for us. You know, I feel like we've all heard about the building blocks of life. But you also call out some other important things. like having a cell membrane. Yes.

Why is that so important? 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 involved in these organic molecules. And the thing again, I will say it again, we find these organic molecules on asteroids, comets, in gas clouds. They're everywhere. So they can spontaneously assemble. That's the idea. They do spontaneously assemble. And not only that, the important organic molecule that we call RNA, experiment after experiment after experiment shows that they all,

also will spontaneously form under the right conditions of energy and temperature and, you know, being in a nice little compartment. Okay, 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 like a cell that has organelles that do jobs? Well, there's one step in that process that we call abiogenesis that is a Nobel Prize waiting for someone to figure out exactly that process. Get on it. Abigensis, what is that? That is the step where you go from non-living inanimate matter to actually living, reproducing matter. Is this like where physical principles meet natural selection? You know what I mean?

Like, I guess I'm wondering why molecules tend to reproduce themselves. You know, there are examples of, you know, non-living matter reproducing itself. The simplest example is a crystal, right? Crystals reproduce themselves. We take advantage of that when we grow the silicon waferes that we use for our electronics. But the process of, you know, 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, right? 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, you have hot water coming out of the vent, and then you have cold water surrounding it. So you could imagine that such a cell while in the cold water will be stable, but when it hits the hot water, it may break apart, right?

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 know because I'm not one of them on that topic. But as far as I know, I have no idea how that step took place. I feel better. You know, Hakeem, the thing I felt reading your book was just like how profoundly miraculous it is that I'm here at all, that you and I are having this conversation right now. You know, it just seems so improbable.

I don't know, my mind can't really even hold it. You know, I see it as improbable but inevitable because the universe does things in big numbers, right? Yes, yes. Our galaxy has 400 billion stars or so, and there's hundreds of billions of galaxies in the observable universe alone. And so, you know, if you look at many of the steps necessary, the, the, you know, the universe, 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 sales is about potential. And once you have that potential, you have that possibility. And given the

large numbers of planets and stars and galaxies, it becomes an inevitability. But how you go from there to large multicellular life and then to intelligence, that is where you need that water bathed in sunlight. And not every, 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.

Amazing. Before we go, you write a lot about imagination. Yes. And I loved that. What do you think the role of imagination is in science? 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, right? 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, right?

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. Happy Earth Week, Hakeem.

Thank you so much. You as well, Flora. Astrophysicist Hakim Olu-Shei 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 Science Friday.com slash exist. Speaking of Earth Week, we recently got a call from a listener about other planetary issues. Hello, my name is Andrew calling from Sacramento, California. Was this finishing listening to the episode titled, Should Please Please Let Be U.S. Sanit 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. 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. 8774 Cy Fright is our number. And we'll see what we can do. This podcast was produced by Charles Berkwist. Thank you for listening.

I'm Flor Lichten.